Lynchevsky theory of metallurgical processes. Tutorial: the theory of metallurgical processes. Chapter XVII. Production of seamless and welded pipes

Federal Agency for Education

GOU VPO "Ural State Technical University - UPI"

A.M. Panfilov

Educational Electronic Text Edition

Prepared by the Department of "Theory of Metallurgical Processes"

Scientific Editor: Prof., Dokt. Chem. Sciences MA Spiridonov

Methodical indications of laboratory work on the physicochemistry of metallurgical systems and processes "," Theory of Metallurgical Processes "for students of all forms of training of metallurgical specialties.

Regulated rules for the organization of work in the workshop "Theory of Metallurgical Processes" Department of TMP (Specialized Audience

MT-431 them. O.A. Yesin). The methodology and procedure for the implementation of laboratory work are described, the requirements for the content and registration of reports on laboratory work according to the current gtostas and recommendations on their implementation are described.

Yekaterinburg

Introduction ................................................... .................................................. .................................................. . four

1 Organization of work in the laboratory workshop on the theory of metallurgical processes ............. 4

1.1 Preparation for laboratory work ............................................. .................................................. .. 5 1.2 Recommendations for processing measurement results and registration of the report .............................. 5

1.3.1 Building graphs ............................................. .................................................. ................... five

1.3.2 Smoothing experimental data ............................................ ................................... 7.

1.3.5 Numerical differentiation of a function set by a set of discrete points ................ 8

approximating some set of data .............................................. .................................. nine

1.3.7 Presentation of the results ............................................. .................................................. ....... 10

2 Description of laboratory work .............................................. .................................................. ............. eleven

2.1 Studying the kinetics of high temperature oxidation of iron (work number 13) ......................... 12

2.1.1 General laws of iron oxidation ........................................... .................................. 12 2.1.2 Description of the installation and the procedure for conducting experiments ...... .................................................. ..... fourteen

2.1.3 Processing and presentation of measurement results ............................................ ................... fifteen

Control questions................................................ .................................................. ..................... 17.

2.2 Study of the temperature dependence of the specific electrical conductivity of oxide melts

(Work number 14) ............................................. .................................................. .......................................... nineteen

2.2.1 General information about the nature of the electrical conductivity of slags ...................................... 19

2.2.2 Description of the installation and measurement techniques .......................................... ................................ 21.

2.2.3 Working order ............................................ .................................................. ..... 23.

2.2.4 Processing and presentation of measurement results .......................................... ................... 24.

Control questions................................................ .................................................. ..................... 25.

2.3 Study of the kinetics of desulfurization metal slag on a simulation model (work number

15) ............................................................................................................................................................ 26

2.3.1 General information about the kinetics of desulfurization metal slag ........................................ ..... 26.

2.3.2 Mathematical model of the process ............................................ ............................................... 29

2.3.3 Working order ............................................ .................................................. ...... thirty

2.3.4 Processing and presentation of measurement results .......................................... ................... 31

Control questions................................................ .................................................. ..................... 32.

2.4 Thermographic study of the processes of dissociation of natural carbonates (work No. 16) 33

2.4.1 General patterns of dissociation of carbonates ........................................... ...................... 33.

2.4.2 Installation scheme and work technique ......................................... ......................... 39.

2.4.3 Processing and presentation of measurement results ............................................ ................... 39.

Control questions................................................ .................................................. ..................... 41.

2.5 Studying the temperature dependence of the viscosity of oxide melts (work number 17) ............. 42

2.5.1 The nature of the viscous resistance of oxide melts .......................................... ................ 42.

2.5.2 Description of the installation and methods of measurements of viscosity ......................................... .................. 43.

2.5.3 Working order ............................................ .................................................. ...... 45.

2.5.4 Processing and presentation of measurement results ............................................ ................... 45 Control Questions ............................ .................................................. ......................................... 46.

2.6 Restoration of manganese from oxide melt in Steel (work number 18)

2.6.1 General laws of electrochemical interaction of metal and slag ............... 47

2.6.2 process model ............................................. .................................................. ........................ 49.

2.6.3 Working order ............................................ .................................................. ...... fifty

Control questions................................................ .................................................. ..................... 52 List of references .......................... .................................................. .................................................. ..... 53.

STP UPTU-UPI 1-96	Standard enterprise. General requirements and rules for registration of diploma and course projects (works).
GOST R 1.5-2002	GSS Standards. General requirements for building, presentation, design, content and designation.
GOST 2.105-95	ESKD. General requirements for text documents.
GOST 2.106-96	ESKD. Text documents.
GOST 6.30 2003.	USD Unified system of organizational and repairing documentation. Requirements for paperwork.
GOST 7.32-2001	Sibid. Report on research work.
GOST 7.54-88	Sibid. Presentation of numerical data on the properties of substances and materials in scientific and technical documents. General requirements.
GOST 8.417-2002	GOOSI. Units of quantities

Designations and abbreviations

	State Standard for the Former USSR or Interstate Standard (Currently).
	Standard adopted by the State Committee of the Russian Federation on Standardization and Metrology (Gosstandart of Russia) or the State Committee of the Russian Federation on Housing and Construction Policy (Gosstroy Russia).
	State standardization system.
	State system for ensuring uniformity of measurements.
	Information Technology
	Least square method
	Personal Computer
	Standard of the company
	Theory of metallurgical processes

Introduction

The implementation of laboratory work on the study of properties in the system of metal slags and processes occurring in metallurgical units makes it possible to better understand the possibilities of the physicochemical method of analysis and get the skills of its practical application. Additionally, the student meets with the implementation of some methods of experimental and model research of individual physicochemical properties and metallurgical processes in general, acquires processing, analysis and submission of experimental information.

1 Organization of work in a laboratory workshop on the theory of metallurgical processes

In the laboratory workshop on the theory of metallurgical processes, the main is the computer collection of experimental information. This determines a number of features of the organization of work:

Each student receives an individual task, performs a whole experiment or the specified part of it and processes the information received. The result of the work includes the resulting numerical characteristics of the studied phenomenon and the errors of their definition, graphics illustrating the identified features, and the conclusions obtained throughout the combination of information. The discrepancy of the quantitative results of the work given in student reports, compared with the control estimates, should not exceed 5%.

The main option for designing results is the processing of experimental data, building charts and formulation of conclusions in Microsoft.Excel electronic tables or OpenOffice.calc.

According to the teacher's resolution, a handwriting report with the necessary illustrations and with graphs made on millimeter paper is temporarily allowed.

The report on the laboratory work is transferred to the teacher leading laboratory workshops, not later than on the working day preceding the next laboratory work. Transmission order (by e-mail, in a break to any teacher or laboratory manner leading at the moment) defines the teacher.

Students who have not submitted a report on previous works and not undergoing colloquium (testing) are not allowed to the next laboratory work.

Only students who have completed introductory instructions on measures of safe work in the laboratory workshop and the instruction in the instruction on the instruction in accounting are allowed to perform laboratory work.

Working with heating and measuring electrical devices, with chemical dishes and reagents is carried out according to safety instructions in the laboratory.

After performing the work, the student puts in order a workplace and gives it a laboratory assistant.

1.1 Preparation for laboratory work

The main sources in preparing for the lesson are the present guide, textbooks and training aids recommended by the lecturer, lectures.

Preparing for laboratory work, a student during the week preceding the lesson should read and understand the material related to the studied phenomenon, to deal with the schemes in the manual in the design of the installation and measurement methodology and the processing of their results. In case of difficulty, it is necessary to use the recommended literature and counseling of the lecturer and teachers leading laboratory classes.

The readiness of the student to fulfill the work is controlled by the teacher by an individual survey of each student, or conducting computer testing. Insufficiently prepared student is obliged to explore the material related to this work during the classes, and the experimental part of the work is performed at an additional lesson after re-inspection. The time and order of repeated occupations is governed by a special schedule.

1.2 Recommendations for processing measurement results and reporting

According to GOST 7.54-88, experimental numerical data should be represented as entitled tables. Samples of tables are offered for each laboratory work.

When processing measurement results, it is necessary to use statistical processing: to use smoothing experimental data, use the method of smallest squares when evaluating dependency parameters, etc. And be sure to evaluate the error of the values \u200b\u200breceived. To perform such processing in spreadsheets, special statistical functions are provided. The required set of functions is also available in calculators intended for scientific (engineering) calculations.

1.3.1 Building graphs

When performing experiments, as a rule, the values \u200b\u200bof several parameters are simultaneously fixed. Analyzing their relationship, you can make conclusions about the observed phenomenon. The visual representation of numerical data extremely facilitates the analysis of their relationship - that's why the construction of graphs is such an important stage of working with information. Note that among the fixed parameters there is always at least one independent variable - the value of which changes in itself (time) or which the experimenter specifies. The remaining parameters are determined by the values \u200b\u200bof independent variables. When building graphs should be guided by some rules:

The value of an independent variable is deposited along the abscissa axis (horizontal axis), and the value of the function is delayed along the ordinate axis (vertical axis).

The scale of the axes should be chosen so as to use the graphics area as informative as possible to be less empty areas on which experimental points and lines of functional dependencies are missing. To fulfill this requirement, often at the beginning of the coordinate axis have to specify a non-zero value. At the same time, all experimental results must be presented on the chart.

Values \u200b\u200bon the axes should, as a rule, multiple some integer (1, 2, 4, 5) and are uniformly. It is categorically unacceptable to indicate the results of specific measurements on the axes. Selected large-scale units should not be too small or too large (should not contain several leading or final zeros). To ensure this requirement, a large-scale factor of the form 10 should be used, which is carried out in the axis designation.

The line of functional dependence must be either a straight or smooth curve. Connect the experimental points of the broken line is permissible only at the preliminary analysis phase.

When building charts with electronic tables, compliance with many of these requirements will be provided automatically, but usually not all and not fully, therefore almost always have to adjust the obtained view.

In the spreadsheets there is a special service - Master Charts (Main Menu: Insertion Chart). The simplest option to appeal to it is to pre-select the area of \u200b\u200bthe cells, including the argument and the function (several functions), and activate the "Master Chart" button on the standard panel.

In this way, you will get a blank of a graph with which you still need to work, since the automatic selection of many parameters of the schedule adopted by default is likely to ensure that all requirements are fulfilled.

First of all, check the size of the numbers on the axes and letters in the designations of the axes and the signatures of the functions in the legend. It is desirable that the font size is the same everywhere, at least 10 and not more than 14 points, but it will be necessary to set the value for each inscription separately. To do this, bring the cursor to the object of interest (axis, signature, legend) and click the right mouse button. In the context menu that appears, select "Format (Element)" and in the new menu on the sheet with the "Font" label to select the desired value. When formatting an axis, additionally see and, possibly, change the values \u200b\u200bon leaves with the "scale" and "number" labels. If you do not understand which changes will result in the proposed choice - do not be afraid to try any option, because you can always refuse the changes made by pressing the Ctrl + Z keys, or selecting the Edit Main menu item - cancel, or by clicking on the button. "Cancel" on the standard toolbar.

If there are a lot of points, and the scatter is small and the line looks sufficient enough, then the points can be connected with lines. To do this, move the cursor to any point on the graph and press the right mouse button. In the context menu that appears, select "Data Series Format". In a new window on a leaflet with a shortcut "View", select the suitable color and thickness of the line, and at the same time check the color, size and shape of the points. Thus, the dependences that approximate experimental data are building. If the approximation occurs a straight line, then two points along the edges of the change of the argument change. Use the "Smoothed Curve" option built into the spreadsheet option is not recommended due to lack of ability to adjust the smoothing parameters.

1.3.2 Smoothing Experimental Data

For experimental data obtained on high-temperature experimental installations, a large amount of random measurement error is characteristic. This is determined mainly by electromagnetic interference from the operation of a powerful heating device. Significantly reduce random error allows statistical processing of results. It is known that for a random variable distributed according to the normal law, the error of the average arithmetic, determined from N. Values, B. N. ½ times less than the error of a single dimension. With a large number of measurements, when it is permissible to assume that a random data spread on a small segment significantly exceeds a natural change in the value, effective smoothing reception is assigning the next value of the measured value of the average arithmetic, calculated by several values \u200b\u200bin the symmetric interval around it. Mathematically, this is transmitted by the formula:

(1.1)

and it is very easily implemented in spreadsheets. Here y. i - measurement result, and Y. I - the smoothed value used instead of it.

For experimental data obtained using digital information collection systems, a random error is characterized, the distribution of which differs significantly from the normal law. In this case, the use of medians instead of the average arithmetic can be more efficient. In this case, the measured value in the middle of the interval is assigned the value of the measured value, which was closest to the middle arithmetic. It would seem a small difference in the algorithm can very significantly change the result. For example, in the embodiment of the median evaluation, some experimental results may be generally unused, most likely those that are really

"Popping" with values \u200b\u200bwith a particularly big error.

1.3.5 Numerical differentiation of a function set by a set of discrete points

The need for such an operation in the processing of experimental points arises quite often. For example, the differentiation of the dependence of the concentration of the concentration on time is the dependence of the speed of the process from time and on the concentration of the reagent, which, in turn, makes it possible to estimate the reaction procedure. Operation of numerical differentiation of a function specified by a set of its values \u200b\u200b( y.) corresponding to the corresponding set of argument values \u200b\u200b( x.), is based on an approximate replacement of the differential function of the relationship of its final change to the final change in the argument:

(1.2)

Numerical differentiation is sensitive to errors caused by the inaccuracy of the source data, discarding the members of the row, etc., and therefore should be carried out with caution. To increase the accuracy of the evaluation of the derivative (), they try to first smooth out the experimental data, at least on a small segment, and only then perform differentiation. As a result, in the simplest case for equidate nodes (the values \u200b\u200bof the argument differ from each other to the same value of X) the following formulas are obtained: for the derivative in the first ( h. 1) point:

for a derivative at all other points ( x.) In addition to the last:

for the derivative in the latter ( x.) Point:

If experimental data is quite a lot and permissible to neglect several extreme dots, the formulas of stronger smoothing can be used, for example, 5 points:

or 7 points:

For uneven arrangement of nodes, we will restrict that we recommend using the modified formula (1.3) in the form of

(1.8)

and in the initial and end points of the derivative not to calculate.

Thus, to implement numerical differentiation, you need to place suitable formulas in the cells of the free column. For example, the unequal values \u200b\u200bof the argument are located in the "A" column in the cells from the 2nd to the 25th, and the function values \u200b\u200bin the "B" column in the corresponding cells. The values \u200b\u200bof the derivative are supposed to be placed in the column "C". Then in the C3 cell should be introduced formula (5) in the form:

\u003d (B4 - B2) / (A4 - A2)

and copy (stretch) into all cells in the C4 range: C24.

1.3.6 Determination by the method of the smallest squares of the polynomial coefficients,

approximating some set of data

With a graphical representation of numerical information, the need often arises to carry out the experimental points of the line, detecting the features of the dependence obtained. This is done for better perception of information and facilitate further analysis of data having some scatter due to measurement errors. Often, on the basis of theoretical analysis of the studied phenomenon, it is known in advance which kind of this line should have. For example, it is known that the dependence of the speed of the chemical process ( v.) The temperature should be exponential, and the exponent in the indicator shows the inverse temperature in the absolute scale:

This means that on the schedule in the coordinates of LN v. - 1 / t should be straight line,

the angular coefficient of which characterizes the activation energy ( E.) process. Through experimental points, as a rule, several direct, having different angular coefficients can be carried out. In a certain sense, the best of them will be straight with coefficients determined by the smallest square method.

In general, the least squares are found by the coefficients of the approximating dependence y. (x. 1 , x. 2 ,…x N.) Polynomial view

where b. and m. 1 …m N. - constant coefficients, and x. 1 …x N. - A set of independent arguments. That is, in general, the method is used to approximate the function of several variables, but it is applicable to describing the complex function of one variable x. . In this case, it is usually believed that

and the approximating polynomic

When choosing an approximating polynomial n. Keep in mind that it must be less than the number of measured values. x. and y. . Almost in all cases, it should be no more than 4, rarely 5.

This method is so important that there are at least four options for obtaining the values \u200b\u200bof the desired coefficients in Excel spreadsheet. We recommend using the linear () function if you work in Excel spreadsheets as part of Microsoft Office, or the Linest () function in CALC spreadsheets in OpenOffice. They are presented in the list of statistical functions, refer to the class, so-called, matrix functions and have a number of features of application. First, it is not entered into one cell, but immediately in the range (rectangular area) of the cells, since the function returns several values. The size of the horizontal area is determined by the number of the coefficients of the approximating polynomial (in the example of their example two: ln v. 0 and E / R), and vertically can be allocated from one to five lines depending on which amount of statistical information is necessary for your analysis.

1.3.7 Presentation of results

In a scientific and technical document, when presenting numerical data, an assessment of their authenticity and a random and systematic error are allocated. The above data errors should be presented in accordance with GOST 8.207-76.

With statistical processing of a group of observation results, the following operations should be performed: eliminate well-known systematic errors from observation results;

Calculate the average arithmetic corrected observation results adopted for the measurement result; calculate the estimate of the average quadratic deviation of the measurement result;

Calculate the trust borders of a random error (random component of the error) of the measurement result;

Calculate the boundaries of a non-exclusive systematic error (non-exclusive residues of systematic error) measurement result; Calculate the confidence limits of the measurement result error.

To determine the trust borders of the error of the measurement result, the trustful probability R Take an equal to 0.95. With a symmetrical trust error, the measurement results are presented in the form:

where - the result of the measurement, Δ - the measure of measurement error boundary, R - Trustful probability. The numeric value of the measurement result should be ended in the number of the same discharge as the error value Δ.

2 Description of laboratory work

In the first part of each of the partitions on specific laboratory work, information on the composition and structure of the phases, the mechanism of processes occurring within the phase or on the borders of its partition with adjacent phases, is minimal to understand the being studied in the work of the phenomenon. If the information provided is not enough, it should be addressed to the abstract of lectures and the recommended literature. Without an understanding of the first part of the section, it is impossible to imagine what happens in the system under study during the performance of work, formulate and comprehend the conclusions on the results obtained.

The next part of each section is devoted to the hardware or software implementation of the real installation, or a computer model. Here are information about the equipment used and the algorithms used. Without an understanding of this section, it is impossible to estimate the sources of errors and what actions should be taken to minimize their influence.

In the last part, the procedure for performing measurements and processing their results is described. All these questions are taken out of the colloquium preceding work, or computer testing.

2.1 Study of the kinetics of high-temperature iron oxidation (work number 13)

2.1.1 General of iron oxidation patterns

According to the principle of the sequence of transformations A.A. Baikov on the surface of the iron during its high-temperature oxidation of air oxygen is formed by all the thermodynamically stable oxides in these conditions. At temperatures above 572 ° C, the scale consists of three layers: Ashtita Feo, the FE 3 Magnetite, FE 2, 3 o 3 hematite, the vestite layer, which is approximately 95% of the thickness of the entire scale, has r-semiconductor properties. This means that in the FEO cationic sublattice there is a significant concentration of vacancies of bivalent iron, and the electronic refoitality is provided by the appearance of electronic "holes", which are particles of trivalent iron. Anionic Vyutita Celebration, consisting of negatively charged ions about 2-, almost lowless, the presence of vacancies in the cationic sublattice significantly increases the diffusion mobility of FE 2+ particles through the vestite and reduces its protective properties.

The intermediate layer of magnetite - the oxide of a stoichiometric composition having a small concentration of defects in the crystal lattice and possessing this in elevated protective properties. The relative thickness is an average of 4%.

The outer layer of scale - hematite has the conductivity of N-type. The presence of oxygen vacancies in the anionic sublattice facilitates diffusion through it of oxygen particles, compared with iron cations. The relative thickness of the FE 2 layer 3 does not exceed 1% .

At temperatures below 572 ° C, the yaws are thermodynamically unstable, therefore the scale consists of two layers: the magnetite Fe 3 O 4 (90% thickness) and hematite Fe 2 O 3 (10%).

The formation of a continuous protective film from the scale on the surface of the iron leads to its separation from the air atmosphere. Further oxidation of metal is carried out due to diffusion of reagents through an oxide film. The heterogeneous process under consideration consists of the following stages: submission of oxygen from the volume of the gas phase to the border with oxide by molecular or convective diffusion; o2 adsorption on oxide surface; ionization of oxygen atoms with the formation of anions about 2-; diffusion of oxygen anions in the oxide phase to the border with the metal; ionization of iron atoms and switching them to scale in the form of cations; Diffusion of iron cations in oxide to the border with gas; Crystalochemical act of formation of new portions of the oxide phase.

The diffusion mode of metal oxidation is implemented if the most inhibited stage is the transport of particles Fe 2+ or O 2- through scale. The supply of molecular oxygen from the gas phase is carried out relatively quickly. In the case of a kinetic mode, the stages of adsorption or ionization of particles are limiting, as well as the act of crystal chemical transformation.

The output of the kinetic equation of the iron oxidation process for the case of a three-layer scale is quite cumbersome. It can be significantly simplified without changing the final conclusions, if we consider the scale of homogeneous in the composition and take into account the diffusion through it only Fe 2+ cations.

Denote by D. FE 2+ Particle diffusion coefficient in Okalin, k. - iron oxidation rate constant, C. 1 I. FROM 2 equilibrium concentration of iron cations on the border with metal and air, respectively, h. - the thickness of the oxide film, S. - sample surface area - oxide density, M. - Its molar mass. Then, in accordance with the laws of formal kinetics, the specific speed of the chemical act of the interaction of iron with oxygen per unit surface of the sample ( v R.) Determined by the relation:

In the stationary state, it is equal to the density of the diffusion flow of FE 2+ particles.

Considering that the total speed of the heterogeneous oxidation process is proportional to the growth rate of its mass

(13.3)

can be excluded C. 2 of equations (13.1) and (13.2) and obtain the dependence of the mass of scale from time to time:

(13.4)

From the last ratio it can be seen that the kinetic process mode is implemented, as a rule, in the initial moment of oxidation, when the thickness of the oxide film is small and its diffusion resistance can be neglected. The growth of the scale layer slows the diffusion of reagents, and the process mode changes to the diffusion.

A more stringent approach, developed by Wagner in the ion-electo theory of high-temperature metal oxidation, allows you to quantify the constant speed of the parabolic film growth law using the data of independent experiments on the electrical conductivity of oxides:

where Δ. G. - change in Gibbs energy for metal oxidation reaction, M. - molar mass of oxide - its electrical conductivity, t I. - share of ionic conductivity, z. - Metal valence, F. - Permanent Faraday.

When studying the kinetics of the formation of very thin ( h. < 5·10 –9 м) пленок необходимо учитывать также скорость переноса электронов через слой оксида путем туннельного эффекта (теория Хауффе и Ильшнера) и ионов металла под действием электрического поля (теория Мотта и Кабреры). В этом случае окисление металлов сопровождается большим самоторможением во времени при замедленности стадии переноса электронов, чему соответствует логарифмический закон роста пленок h. = K. · Ln ( a. τ+ B.), as well as cubic h. 3 = K. · Τ (oxides - semiconductors p. -Type) or reverse logarithmic 1 / h. = C. K. · Ln (τ) ( n- The type of conductivity) during the slowdown of the metal ion transfer stage.

2.1.2 Description of the installation and the procedure for conducting experiments

The kinetics of iron oxidation is studied using a gravimetric method that allows you to fix the change in the mass of the sample over time during the experience. The installation scheme is shown in Figure 1.

Figure 1 - Experimental installation scheme:

1 - the studied iron sample; 2 - electrical resistance furnace; 3 - Mechanoelectric converter E 2D1; 4 - Personal computer with ADC board.

Metal sample (1), suspended on the nichrome chain to the rocker of the mechanoelectric converter E 2D1 (3), is placed in a vertical tubular furnace of electrical resistance (2). The output signal E 2D1, proportional to the change in the mass of the sample, is supplied to the board of the computer's ADC as part of the installation. The constancy of the temperature in the furnace is maintained by an automatic regulator, the necessary experience temperature is set by the corresponding toader on the furnace dashboard as directed by the teacher (800 - 900 ° C).

According to the results of the work, it is determined by the rate constant of the iron oxidation reaction and the diffusion coefficient of its ions in the oxide film and, if possible, the activation energy of the chemical reaction and diffusion. Graphically illustrate the dependence of the change in the mass of the sample and the speed of the oxidation process.

2.1.3 Processing and presentation of measurement results

The mechanoelectric converter is arranged in such a way that part of the mass of the measurement object is compensated by a spiral spring. The magnitude of it is unknown, but it must remain constant during measurements. As follows from the description of the measurement techniques, the accurate time (0) of the beginning of the oxidation process is not known, since it is unknown when the sample will acquire a temperature sufficient for the development of the oxidation process. Until that time when the sample really starts to oxidize, its mass is equal to the mass of the starting metal ( m. 0). The fact that we measure not all the mass is, but only its uncompensated part, the creature does not change. The difference between the current sample mass ( m.) and the starting mass of the metal is a mass of scale, so formula (13.4) for real experimental conditions should be represented as:

(13.6)

in which m. - measured value of the remaining uncompensated part of the sample mass, m 0. - The same before the oxidation process at low sample temperature. From this ratio, it can be seen that the experimental dependence of the mass of the sample from time should be described by the equation of the form:

, (13.7)

the coefficients of which on the obtained measurement results can be found by the smallest square method. The said illustrates a typical schedule in fig. Points - measurement results, line was obtained by approximation of data by equation 13.7

Points marked with cross are poppies and should not be considered when calculating the coefficients of equation 13.7 by the smallest square method.

Comparing formulas (13.6) and (13.7) it is easy to associate the found coefficients with the determining physico-chemical values:

(13.8)

In the example above, the value of M0 is the value on the ordinate axis at \u003d 0, it turned out to be 18.1 mg.

Using these values \u200b\u200bobtained in preparation for the experience of the sample area ( S.) and borrowed from the literature data of the density of Vyutit (\u003d 5.7 g / cm 3)

assess the ratio of the diffusion coefficient and the rate constant of the oxidation process:

(13.13)

This ratio characterizes the thickness of the scale of the scale, at which the diffusion rate constant is equal to the velocity constant of the chemical metal oxidation reaction, which corresponds to the definition of a strictly mixed reaction mode.

According to the results of work, all values \u200b\u200bshould be determined using formulas (13.7, 13.11 - 13.13): b. 0 , b. 1 , b. 2 , m. 0, 0 and D. /K. . To illustrate results, you should bring a graph m. -. Along with experienced values, it is desirable to bring an approximating curve.

According to the measurement results, you must fill out the following table:

Table 1. Results of the process of iron oxidation process.

In the table, the first two columns are filled after opening the data file, and the rest are calculated. Smoothing is performed by 5 points. When determining the coefficients of the approximating polynomial, the first, third and fourth columns are simultaneously used. In the last column, the results of approximation by polynomial (13.7) using the lowest squares found by the least squares found by the method of smallest squares of the coefficients. The schedule is built on the first, third and fifth columns.

If work is performed by several students, each of them conducts experience at its temperature. Joint processing of the results of estimation of the thickness of the scale of the scale in strictly mixed mode () allows you to estimate the difference in the activation of diffusion and chemical reaction. Indeed, the obvious formula is true here:

(13.14)

Similar processing of coefficients b. 2 allows you to evaluate the activation energy of diffusion. The formula is true here:

(13.15)

If the measurements were carried out at two temperatures, estimates are performed directly by formulas (13.4) and (13.15), if the temperature values \u200b\u200bare more than two, the least squares method should be applied for functions. lN. () – 1/T. and lN. (b 2.) – 1/T. The obtained values \u200b\u200blead in the final table and are discussed in conclusions.

Procedure for processing work results

2. Build on a separate sheet a graph m. -, Visually reveal and remove population values.

3. Perform the smoothing of the measured mass values.

4. Calculate Mass Change Squares

5. Find the least squares method coefficients b. 0 , b. 1 , b. 2 equations, approximating the dependence of the mass change over time.

6. Calculate the mass estimate at the beginning of measurements in accordance with the approximating equation

7. To analyze the results of approximation using sorting and exclude incorrect values

8. Display the results of approximation on a dependency schedule m. – .

9. Calculate the characteristics of the system and process: m. 0 , 0 , D. /K. .

Counting results:

a. In the cell "A1" - the surface area of \u200b\u200bthe sample, in the adjacent cell "B1" units of measurement;

b. In the cell "A2" - the mass of the original sample, in the cell "B2" - units of measurement;

c. In the cell "A3" - the temperature of the experience, in the cell "B3" - units of measurement;

d. In the cell "A4" - the thickness of the scale layer in strictly mixed mode, in the cell "B4" - units of measurement;

e. Starting from the cell "A10" should be clearly formulated conclusions for work.

In the cells of A6-A7, there must be references to cells on other sheets of the book of spreadsheets on which calculations are made to obtain the result presented, and not the numeric values \u200b\u200bthemselves! If this requirement is not fulfilled, the verification program gives the message "information presentation error".

2. Correctly decorated graph m. - obtained experimentally (points) and approximated polynomial (line), on a separate sheet of spreadsheets with all the necessary signatures and notation.

Control questions

1. What is the structure of the scale obtained on the gland during its high-temperature oxidation in the air atmosphere?

2. Why does the appearance of the existing phase in the scale leads to a sharp increase in iron oxidation rate?

3. What stages are the heterogeneous iron oxidation process?

4. What is the difference between the diffusion regime of iron oxidation from kinetic?

5. What are the order and methods of working?

6. How to identify the mode of oxidation process?

2.2 Study of the temperature dependence of the electrical conductivity of oxide melts (work number 14)

2.2.1 General information about the nature of the electrical conductivity of slags

The study of the dependence of the specific electrical conductivity of slags from their composition and temperature is of great importance for metallurgy both in theoretical and applied. The value of the specific electrical conductivity can have a significant effect on the speed of the most important reactions between the metal and slag in steel production processes, on the performance of metallurgical units, especially in electrical shield and arc furnaces for smelting the synthetic slag, where the intensity of heat isolation depends on the magnitude of the electric current is passed. In addition, the specific conductivity, being a structurally sensitive property, provides indirect information on the structure of the melts, concentration and the form of charged particles.

According to the idea of \u200b\u200bthe structure of oxide melts, formulated, in particular, the scientific school of Professor O.A. Isin, uncharged particles cannot be present in them. At the same time, the ions in the melt differ greatly in size and structure. The elements of the main oxides are present in the form of simple ions, for example, Na +, Ca 2+, Mg 2+, Fe 2+, O 2-. On the contrary, elements with high valence, which form acidic (acidic) oxides, such as SiO 2, TiO 2, B 2 O 3, in the form of ion have such a high electrostatic field, which cannot be in the melt as simple Si 4+ ions, Ti 4+, B 3+. They so much closer to oxygen anions that form covalent bonds with them and are present in the melt in the form of complex anions, the simplest of which are, for example, SiO 4 4, TiO 4 4-, BO 3 3-, BO 4 5-. Complex anions have the ability to complicate their structure, uniting in two- and three-dimensional structures. For example, two silicial chicken tetrahedra (SiO 4 4-) can be connected by vertices by forming the simplest linear chain (Si 2 O 7 6-). At the same time, one oxygen ion is released:

SiO44- + SiO44- \u003d Si2O76- + O2-.

These questions can be viewed in more detail, for example, in educational literature.

Electrical resistance R. Conventional linear conductors can be determined from the ratio.

where is the resistivity, L. - Length, S. - Cross-section area of \u200b\u200bthe conductor. The value is called the specific conductivity of the substance. From formula (14.1) follows

The dimension of the electrical conductivity is expressed in OM -1 M -1 \u003d cm / m (cm - Siemens). The electrical conductivity characterizes the electrical conductivity of the volume of the melt concluded between two parallel electrodes having an area of \u200b\u200b1 m 2 and located at a distance of 1 m from each other.

In a more general case (inhomogeneous electric field), specific electrical conductivity is defined as the proportionality coefficient between current density i. In conductor and electric potential gradient:

The appearance of electrical conductivity is associated with the transfer of charges in the substance under the action of the electric field. In metals in the transfer of electricity, the electrons of the conduction zone are involved, the concentration of which is practically independent of temperature. With increasing temperature, there is a decrease in the electrical conductivity of metals, because The concentration of "free" electrons remains permanent, and the inhibitory effect on them of the thermal motion of the ions of the crystal lattice increases.

In semiconductors, the electrical charge carriers are quasi-free electrons in the conduction or vacancy zone in the valence energy zone (electronic holes) arising from thermally activated electrons transitions from donor levels into the semiconductor conductivity zone. With increasing temperature, the likelihood of such activated transitions increases, respectively, the concentration of electrical current carriers and electrical conductivity increases.

In electrolytes, to which oxide melts include, in the transfer of electricity, they are involved, as a rule, ions: Na +, Ca 2+, Mg 2+, SiO 4 4-, BO 2 - and others. Each of the ions ј The variety can give its contribution to the total amount of electric current density in accordance with the known ratio

where is partial specific electrical conductivity; D ј. , C ј. , z ј. - Diffusion Coefficient, Concentration and Charity of Ion ј -Ho varieties; F. - Permanent Faraday; T. - temperature; R.

Obviously, the amount of values i ј. equal to total current density i. associated with the movement of all ions, and the specific electrical conductivity of the entire melt of the amount of partial conductors.

The movement of ions in electrolytes is an activation process. This means that under the action of the electric field, not all ions are moved, but only the most active of them, which have a certain excess of energy compared with the average level. This excess energy, called electrical conductivity activation energy, is necessary to overcome the interaction forces of this ion with a surroundings, as well as for the formation of a vacancy (cavity) in which it passes. The number of active particles, in accordance with the law of the Boltzmann, is growing with

increasing temperature according to the exponential law. therefore . Followed

in accordance with (14.5), the temperature dependence of the electrical conductivity should be described by the amount of exponential. It is known, however, that with an increase in particle size, their activation energy is significantly increasing. Therefore, in relation (14.5), as a rule, they neglect the contribution of large sediments, and for the rest averaging partial values.

As a result, the temperature dependence of the specific electrical conductivity of oxide melts takes the following form:

(14.6)

which agrees well with experimental data.

Typical values \u200b\u200bfor metallurgical slags containing oxides of SAO, SiO 2, MGO, AL 2 O 3 are in the range of 0.1 - 1.0 cm · CM -1 near the temperature of the liquids, which is significantly less than the electrical conductivity of liquid metals (10 5 -10 7 cm · cm -1). The activation energy of electrical conductivity almost does not depend on the temperature in the main slags, but can be somewhat decreased with increasing temperature in acidic melts, due to their depolymerization. Typically, the value lies in the range of 40-200 kJ / mol, depending on the composition of the melt.

With elevated contents (over 10%) iron oxides (FeO, Fe 2 O 3) or other transition oxides (for example, MNO, V 2 O 3, CR 2 O 3), the character of the electrical conductivity of slags changes, T to. In addition to ionic in them There is a significant proportion of electronic conductivity. The electronic component of conductivity in such melts is due to the movement of electrons or electronic "holes" along the relay mechanism from the transition metal cation with less valence to the cation with greater valence through r -Evuboli oxygen ion located between these particles.

Very large electron mobility in combination of 2+ - O 2- - ME 3+, despite their relatively small concentration, sharply increases the specific electrical conductivity of slags. So the maximum value æ for purely iron melts FeO - Fe 2 O 3 can be

10 2 cm · cm -1, remaining, however, significantly less metals.

2.2.2 Description of installation and measurement methods

The paper determines the specific electrical conductivity of the molten sodium tetractation Na 2 O · 2B 2 O 3 in the temperature range of 700 - 800 ° C. To eliminate complications associated with the presence of metal resistance, the metal - electrolyte, the study of electrical conductivity must be carried out in such conditions when the boundary resistance is negligible. This can be achieved using instead of a constant alternating current of a sufficiently high frequency (≈ 10 kHz).

The circuit of the electrical installation circuits is shown in Figure 2.

Figure 2. Electric installation chains for measuring the electrical conductivity of slags:

ZG - sound frequency generator; PC - Personal computer with sound payment; Bar rr and bar wish - electrochemical cells containing aqueous solution of KSL or slag, respectively; R fl is the reference resistance of a known value.

AC from the sound frequency generator is fed to a cell containing a slag, and the reference resistance of a known value is sequentially included with it. Using the PC sound card, the voltage drop in the cell and the reference resistance is measured. Since the current flowing through R et and bar, the same

(14.7)

The laboratory installation service program calculates, displays the monitor and writes a ratio of the ratio ( r.) AC amplitude values \u200b\u200bat the output of the audio generator ( U. ZG) and on the measuring cell ( U. bar):

Knowing it, you can define cell resistance

where is a permanent cell.

For determining K. Bar in the experimental installation use an auxiliary cell similar to the studied geometric parameters. Both electrochemical cells are corundum boats with electrolyte. They are omitted in two cylindrical electrodes from the metal of the same cross section and the length located at the same distance from each other to ensure the constancy of the relationship (L / S) Eff.

The conducted cell contains the melt Na 2 O · 2B 2 O 3 and is interfered with the heating furnace at a temperature of 700 - 800 ° C. The auxiliary cell is at room temperature and filled with 0.1 H aqueous solution of KSL, the electrical conductivity of which is 0.0112 cm · cm -1. Knowing the electrical conductivity of the solution and determining (see formula 14.9) electrical resistance

auxiliary cell (

2.2.3 Working procedure

A. Work using the measuring system in real time

Before starting measurements, the furnace should be heated to a temperature of 850 ° C. The procedure for installation is as follows:

1. After executing the initialization procedure, in accordance with the indication on the monitor screen, turn off the furnace, put the switch "1 - reference resistance" to the "1 - Hi" position and follow further instructions.

2. After indicating the "Switch 2 - to the" Solution "position, it is necessary to perform it until the" Switch 2 "indicates the" Melt "position to record the resistance ratios that appear every 5 seconds.

3. Perform the second indication and monitor the temperature change. Once the temperature becomes less than 800 ° C follows the keyboard with the keyboard "XS" to enable the graph output and write the temperature and resistance ratios every 5 seconds.

4. After cooling the melt to a temperature of less than 650 ° C, measurements should be initialized for the second student performing work on this unit. The switch "1 - reference resistance" to put in the "2 - Lo" position and from this point on the second student starts to record the temperature values \u200b\u200band resistance ratios every 5 seconds.

5. When the melt is cooled to a temperature of 500 ° C or achieve the value of the resistance ratio close to 6, it is necessary to stop measurements, feeding the "XE" command from the keyboard. From this point on, the second student must translate the 2 switch to the 'solution' position and write down the ten values \u200b\u200bof the resistance ratio.

B. Working with data previously recorded in the file

After activating the program, a message appears on the screen on the value of the reference resistance and several values \u200b\u200bof the resistance ratio are sequentially displayed ( r.) Calibration cell. After averaging, this data will allow you to find a permanent installation.

In the future, every few seconds on the screen appears the temperature values \u200b\u200band the problem of resistance for the measuring cell. This information is displayed on the graph.

The program automatically completes the work and forwards all the results on the PC of the teacher.

2.2.4 Processing and presentation of measurement results

According to the measurement results, you should fill in the table with the following heading:

Table 1. Temperature dependence of the electrical conductivity of the melt Na 2 O · 2B 2 O 3

In the table, the first two columns are filled after opening the data file, and the rest are calculated. According to them, the ln () - 10 / T dependence schedule should be constructed and using the least squares method (Linest function in OpenOffice.calc) determine the value of activation energy. The graph should be brought by approximating direct. You should also construct a graph of the dependence of electrical conductivity on temperature. Procedure for processing results

1. Enter the records of measurement results to the spreadsheet file.

2. Calculate the average value of the resistance ratio for the calibration cell.

3. Calculate a permanent installation.

4. Build a decision schedule r. – t. Visually reveal and remove pop-up values. With their large quantity to apply sorting.

5. Calculate the resistance of the measuring cell, the electrical conductivity of the oxide melt at different temperatures, the logarithm of electrical conductivity and the inverse absolute temperature

b. 0 , b. 1 equations approximating the dependence of the logarithm of electrical conductivity from the inverse temperature, and calculate the activation energy.

7. Build on a separate sheet a graph of the logarithm of electrical conductivity from the inverse temperature and bring the approximating dependence Counting results:

1. In the book of the spreadsheet presented for verification, the following information should be presented on the first page with the name "Results":

a. In the cell "A1" - the starting temperature, in the cell "B1" - units of measurement;

c. In the cell "A3" - the activation energy of electrical conductivity, in the cell "B3" - units of measurement;

d. In the cell "A4" - a pre-exponential factor in the formula of the temperature dependence of electrical conductivity, in the cell "B4" - units of measurement;

e. Starting from the cell "A5" should be clearly formulated conclusions for work.

In A1-A4 cells, there must be references to cells on other sheets of the book of spreadsheets, which are calculated to obtain the result presented, and not numeric values \u200b\u200bthemselves! If this requirement is not fulfilled, the verification program gives the message "information presentation error".

2. A properly decorated graph of the logarithm of electrical conductivity from the inverse temperature obtained by experimental data (points) and the approximated polynomial (line), on a separate sheet of spreadsheets with all the necessary signatures and notation.

Control questions

1. What is called specific electrical conductivity?

2. What particles determine the electrical conductivity of slags?

3. What is the nature of the temperature dependence of the electrical conductivity of metals and oxide melts?

4. What does the permanent cell depend on and how to determine it?

5. Why should I use alternating current to determine?

6. How does the energy activation energy depends on the temperature?

7. What sensors and devices are used in the laboratory installation. What physical values \u200b\u200bdo they allow register?

8. What are the graphs (in what coordinates) should be presented by the results of work?

9. What physico-chemical values \u200b\u200bshould be obtained after processing the primary data?

10. Decide which measurements are conducted before experience, which values \u200b\u200bare registered during the experience, which data refer to primary information, which processing it is exposed and what information is obtained.

2.3 Study of the kinetics of desulfurization metal slag on the simulation model (work number 15)

2.3.1 General information about the kinetics of desulfurization metal slag

Sulfur impurities in steel, in quantities over 0.005 wt. %, significantly reduce its mechanical, electrical, anti-corrosion and other properties, worsen the weldability of the metal, lead to the appearance of red and coldness. Therefore, the process of desulfuraction of steel, especially effectively flowing with a slag, is of great importance for high-quality metallurgy.

The study of the kinetic patterns of the reaction, detecting its mechanism and the flow regime is necessary to effectively control the rate of desulfuraction, since In real conditions of metallurgical units, the equilibrium distribution of sulfur between metal and slag is usually not achieved.

In contrast to most other impurities in steel, the transition of sulfur from metal into the slag is a process of restorative, and not oxidative 1. [S] + 2e \u003d (S 2-).

This means that for the continuous flow of the cathode process, leading to the accumulation of positive charges on the metal, the simultaneous transition of other particles can be required to give electrons into the metal phase. Such concomitant anode processes may be the oxidation of oxygen anions or iron, carbon, manganese, silicon and other metal impurities, depending on the composition of steel.

2. (O 2-) \u003d [O] + 2e,

3. \u003d (Fe 2+) + 2e,

4. [C] + (O 2-) \u003d CO + 2E, 5. \u003d (Mn 2+) + 2e.

In the aggregate, the cathode and any one anode process allows you to record the stoichiometric equation of the desulfuraction reaction in the following form, for example:

1-2. (Cao) + [S] \u003d (CAS) + [O], H \u003d -240 kJ / mol

1-3. + [S] + (CaO) \u003d (FeO) + (CAS). H \u003d -485 kj / mole

Appropriate expressions for equilibrium constants are viewed

(15.1)

Obviously, the processes chosen as an example and the like they can occur simultaneously. From the relation (15.1) it follows that the degree of desulfuraction of the metal at a constant temperature, i.e. The constant value of the equilibrium constant increases with the increasing concentration of the free oxygen ion (O 2-) in the oxide melt. Indeed, the growth of the factory in the denominator should be compensated by a loss of another factory to fit the constant equilibrium constant. It should be noted that the content of free oxygen ions increases when using highly international rich slag calcium oxide. Analyzing the relation (15.2), it can be concluded that the content of iron ions (Fe 2+) in the oxide melt should be minimal, i.e. Slags must contain a minimum amount of iron oxides. The presence in the metal metal (Mn, Si, Al, C) also increases the completeness of the desulfuraction of steel due to the decrease in the content (Fe 2+) and [o].

The reaction 1-2 is accompanied by heat absorption (ΔH\u003e 0), therefore, as the process flows, the temperature in the metallurgical unit will decrease. On the contrary, the reaction 1-3 is accompanied by heat release (ΔH<0) и, если она имеет определяющее значение, температура в агрегате будет повышаться.

At the kinetic description of desulfurization, the following stages of the process should be considered:

Delivery of sulfur particles from the volume of metal to the border with a slag first due to the convective diffusion, but directly near the boundary of the metal slag section - molecular diffusion; electrochemical act of addition of electrons to sulfur atoms and the formation of anions S 2-; Being an adsorption-chemical act, the removal of sulfur anions into the volume of slag, due to molecular and then convective diffusion.

Similar stages are also characteristic for the anode stages, with the participation of FE, Mn, Si atoms or anions O 2-. Each of the stages contributes to the overall resistance of the desulfurization process. The driving force of the flow of particles through a number of these respeses is the difference of their electrochemical potentials in the non-equilibrium metal system - slag or the difference in the difference of actual and equilibrium electrode potentials on the border of the phase partition, called overvoltage .

The speed of the process consisting of a series of serial stages is determined by the contribution of the stage with the greatest resistance - limit Stage. Depending on the mechanism of the limiting stage, the diffusion or kinetic reaction mode indicate. If the steps with a different flow mechanism have commensurate resistance, then indicate the mixed reaction mode. The resistance of each stage significantly depends on the nature and properties of the system, the concentration of reagents, the intensity of the stirring of the phases, temperature. So, for example, the speed of the electrochemical act of recovery of sulfur is determined by the value of the exchange current

(15.3)

where IN - temperature function, C. [S] and C. (S 2-) - sulfur concentrations in metal and slag, α - transfer coefficient.

The sulfur delivery stage to the phase boundary is determined by the limit current of the diffusion of these particles

where D. [S] - sulfur diffusion coefficient, β is a convective constant, determined by the intensity of convection in the melt, it is proportional to the square root from the linear velocity of the convective flows in the liquid.

Existing experimental data indicate that under normal conditions of convection of the melts, the electrochemical act of the sulfur ion discharge proceeds relatively quickly, i.e. Desulfuraction is inhibited mainly by the diffusion of particles in metal or slag. However, with an increase in sulfur concentration in metal, diffusion difficulties decrease and the process mode may change to kinetic. This also contributes to carbon additives in iron, because The discharge of oxygen ions on the border of carbon metal - slag occurs with significant kinetic braking.

It should be borne in mind that the electrochemical ideas about the interaction of metals with electrolytes allow you to clarify the mechanism of processes, to understand the events occurring in the details. At the same time, simple equations of the formal kinetics fully maintain their justice. In particular, for a rough analysis of the results of the experiment obtained with significant errors, the equation for the reaction rate of 1-3 can be recorded in the simplest form:

where k. F I. k. R - direct and reverse reaction rate constants. This ratio is performed if the solutions of sulfur in the hardware and the calcium sulfide and the yustite in the slag is permissible to be infinitely diluted and the reaction orders of reaction are close to one. The content of the remaining reagents of the reaction under consideration is so great that all the time of interaction remains almost constant and their concentrations can be included in the constant k. F I. k. R.

On the other hand, if the desulfurization process is far from the state of equilibrium, then the rate of reverse reaction can be neglected. Then the rate of desulfuraction should be proportional to the concentration of sulfur in the metal. This variant of the description of the experimental data can be checked by exploring the communication of the desulfurization rate of desulfurization and the logarithm of the sulfur concentration in the metal. If this link is linear, and the angular coefficient of dependence should be close to one, then this is an argument in favor of the process diffusion mode.

2.3.2 Mathematical Model Process

The possibility of several anodic stages is greatly difficult to make a mathematical description of the processes of desulfurization of steel containing many impurities. In this regard, some simplifications were made to the model, in particular, the kinetic difficulties were neglected at

For semi-reacts of the transition of iron and oxygen due to the adopted limit on diffusion control, the relationship looks substantially simpler:

(15.7)

In accordance with the electronics condition in the absence of current from an external source, the connection between currents on separate electrode semi-resources is expressed by a simple ratio:

The difference of electrode overvoltages () is determined by the relations of the corresponding works of activity and equilibrium constants for reactions 1-2 and 1-3:

The derivative of the sulfur concentration in the metal metal is determined by the current of the first electrode half-reaction in accordance with the equation:

(15.12)

Here i. 1 , i. 2 - density of currents of electrode processes, η 1, η 2 - their polarization, i. P - limit current diffusion particles ј - like a variety i. O - Current exchange of the kinetic stage, C. [s] - sulfur concentration in metal, α - transfer coefficient, p, K. P is the work of the activity and the equilibrium constant of the reaction of desulfuraction, S. - the area of \u200b\u200bthe interfacial border Metal slag, V. Me - Metal volume, T. - temperature, F. - Permanent Faraday R. - Universal gas constant.

In accordance with the laws of electrochemical kinetics, expression (15.6) takes into account the injection of diffusion of iron ions in the slag, because, judging by experimental data, the stage of discharge-ionization of these particles is not limiting. The expression (15.5) is the injection of diffusion of sulfur particles in slag and metal, as well as the sulfur ionization slowness on the interfacial border.

Combining expressions (15.6 - 15.12), can be obtained with numerical methods to obtain the dependence of the sulfur concentration in the metal from time to the selected conditions.

The following parameters are used in the model:

3)
Current exchange of sulfur ions:

4) Desulfurization reaction equilibrium constant ( TO R):

5) attitude of the area of \u200b\u200bthe interfacial border to the volume of metal

7) Convective constant (β):

The model allows you to analyze the influence of the listed factors on the speed and completeness of desulfuriation, as well as assess the contribution of diffusion and kinetic braking in the overall process resistance.

2.3.3 Work order

The image generated by the simulation program is represented in Fig. . In the top of the panel, selective numeric values \u200b\u200bof the measured values \u200b\u200bare given, the graph shows all the values \u200b\u200bobtained during the process modeling. In the notation of the components of metallic and slag melts, the metallurgical topics received additional signs are used. Square brackets indicate the belonging of the component with a metal melt, and round-slag. Multipliers for the designations of components are used only to build a schedule, they should not be taken into account when interpreting values. During the model operation, only the value of one of the measured values \u200b\u200bis displayed. After 6 seconds it disappears and the value of the next magnitude appears. During this period of time, you have to have time to record the next value. For time saving, it is recommended that the constant numbers are not recorded, for example, the leading unit in the temperature value.

Five minutes after the start of measurements by the hour in the upper right corner of the installation panel simultaneously pressing the keys and [No.], where No. - the installation number, intense the stirring speed of the phases.

2.3.4 Processing and presentation of measurement results

The measurement results table formed by the simulation program should be supplemented with the following calculated columns:

Table 1. Results of statistical processing of experimental data

The table in the first column should calculate the time from the beginning of the process in minutes.

Further processing is performed after graphic construct - at the first stage of processing, a graph of temperature dependence should be constructed from time to time and evaluate the data range when the sulfur transition accompanies mainly the transition of iron. In this range, two areas are isolated with the same mixing rates and the method of the smallest squares are the coefficients of approximating polynomials of the form:

which follows from equation (15.5) under stipulated conditions. Comparing the obtained values \u200b\u200bof the coefficients make conclusions about the process mode and the degree of system approximation to the state of equilibrium. Please note that there is no free member in equation (15.13).

To illustrate the results of the experiment, graphs of the dependences of the sulfur concentration on the time and the rate of desulfurization from the concentration of calcium sulfide in the slag are constructed.

Procedure for processing results

2. Calculate the speed of the desulfurization process along the sulfur concentration in the metal, the logarithm of the speed and concentration of sulfur.

3. To construct on separate sheets of graphs of temperature dependences in the unit from time to time, the mass of the time, the rate of desulfurability of the time and the logarithm of the desulfurization rate from the logarithm of the sulfur concentration.

4. The method of smaller squares is estimated separately for different mixing rates the kinetic characteristics of the desulfuraction process in accordance with equation () and the procedure for the reaction at the sulfur concentration.

Counting results:

1. Properly decorated graphs of the dependence of the rate of desulfuraction process and the logarithm of this value from time to time, on a separate sheet of spreadsheets with all the necessary signatures.

2. The values \u200b\u200bof the kinetic characteristics of the desulfurization process in all embodiments of the process indicating the dimensions (and errors).

3. Conclusions for work.

Control questions

1. What conditions are required for the most complete desulfurization of metal slag?

2. What are the anodic processes may accompany sulfur removal?

3. From what stages is the process of the transition of sulfur through the interfacial border?

4. In what cases is the diffusion or kinetic desulfuration mode?

5. What is the procedure for performing work?

2.4 Thermographic study of the processes of dissociation of natural carbonates (work number 16)

2.4.1 General Patterns of Dissociation Carbonates

The thermogram is called the dependence of the temperature of the sample from time. The thermographic method of studying the thermal decomposition processes of substances was widespread after the characteristic features of such dependencies were discovered: "Temperature stops" and "inclined temperature sites".

1.4

Figure 3. Illustration of the thermogram:

dotted curve - thermogram of a hypothetical comparison sample, in which dissociation does not occur; The solid line is a real sample with a two-stage dissociation.

These are characteristic sections of dependence, within which for some time (), the temperature either remains constant (t \u003d const), or increases by a small amount (T) at a constant speed (T /). Applying numerical or graphical differentiation can with good accuracy to determine the time and temperature of the beginning and end of the temperature stop.

In the proposed laboratory work, such a dependence is obtained with continuous heating of the natural material of calcite, the main component of which is calcium carbonate. Mountain breed, consisting mainly of calcite, is called limestone. Limestone in large quantities is used in metallurgy.

As a result of firing (thermal processing) limestone by endothermic reaction

Caco 3 \u003d Cao + Co 2

receive lime (CAO) - the desired component of the slag melt. The process is carried out at temperatures below the melting and limestone temperatures and lime. It is known that the carbonates and the oxides formed of them are mutually not soluble, therefore the reaction product is a new solid phase and gas. The expression for equilibrium constant, in the general case, has the form:

Here a. - the activity of solid reagents - the partial pressure of the gaseous product of the reaction. In metallurgy, the other rock is widely used, called dolomite. It mainly consists of a mineral with the same name representing the double salt of CAMG coal acid (CO 3) 2.

Calcite, as well as any natural mineral, along with the main component, contains a variety of impurities, the amount and composition of which depends on the field of natural fossil and, even, from a particular area of \u200b\u200bmining. A variety of impurity compounds is so large that it is necessary to classify them according to some significant in this or that case. For thermodynamic analysis, an essential feature is the ability of impurities to form solutions with reagents. We assume that there are no impurities in the mineral, which in the range studied the range (pressure and temperature) enter into any chemical reactions with each other or the main component or product of its decay. In practice, this condition is not fully strictly carried out, because in calcite, for example, carbonates of other metals may be present, but from the point of view of further analysis, these reactions will not give new information, but unreasonably complicates the analysis.

All other impurities can be divided into three groups:

1. impurities forming a solution with calcium carbonate. Such impurities are certainly necessary to take into account with thermodynamic analysis and, most likely, with a kinetic analysis of the process.

2. impurities dissolving in the reaction product - oxide. The decision of the registration of impurities of this type depends on how quickly their dissolution in the solid product of the reaction and closely associated with the question of the dispersion of the inclusion of impurities of this type. If the inclusions are relatively high in size, and their dissolution occurs slowly, they should not be taken into account during thermodynamic analysis.

3. impurities that are not soluble in the source carbonate and the product of its decay. These impurities should not be considered when thermodynamic analysis, as if they were not at all. In some cases, they can influence the kinetics of the process.

In the simplest (coarse) version of the analysis, it is permissible to combine all impurities of the same type and consider them as some generalized component. On this basis, we highlight three components: B1, B2 and B3. The gas phase of the thermodynamic system under consideration should be discussed. In laboratory operation, the dissociation process is carried out in an open installation communicating with the atmosphere of the room. In this case, the total pressure in the thermodynamic system is constantly and equals one atmosphere, and in the gas phase there is a gaseous product of the reaction - carbon dioxide gas (CO2) and the components of the air medium, simplified - oxygen and nitrogen. The latter do not interact with the rest of the system components, therefore, in the case under consideration, oxygen and nitrogen are not distinguishable and in the future they will be called neutral gaseous components.

Temperature stops and platforms have a thermodynamic explanation. With a well-known phase composition, it is possible to predict the stop temperature with thermodynamic methods. You can solve the inverse problem - at known temperatures, determine the composition of the phases. It is provided for within the framework of this study.

Complete temperature stops and platforms can only be implemented when performing certain requirements for the kinetics of the process. It is natural to expect that these are the requirements of almost equilibrium formulations of the phases at the site of the reaction and neglect small gradients in diffusion layers. Compliance with such conditions is possible if the speed of the process is controlled by non-internal factors (diffusion resistance and the resistance of the chemical reaction itself), and by external - heat supply speed to the reaction site. In addition to the main modes of heterogeneous reaction defined in physical chemistry: kinetic and diffusion, such a process mode is called thermal.

Note that the thermal regime of the solid-phase dissociation process is possible due to the originality of the reaction, which requires the supply of a large amount of heat, and in this case there are no stages of the supply of starting materials to the reaction site (since one substance decomposition) and the decomposition of the solid reaction from the border Section of the phases (as this border moves). Only two stages associated with diffusion: CO2 removal through the gas phase (obviously with very low resistance) and the diffusion of CO2 through oxide, which is greatly facilitated by cracking the oxide filling the volume previously occupied by the fundamental carbon oxide.

Consider the thermodynamic system at temperatures below the temperature stop. First, we assume that there are no impurities in the carbonate of the first and second type. Possible presence of an impurity of the third type take-into account, but only to show that this can not be done. Suppose that the suspension of the studied powder calcite is made up of the same spherical particles with a radius r. 0. The boundary of the thermodynamic system will spend at some distance from the surface of one of the calcite particles, a small compared to its radius, and thus we turn on the system of some volume of the gas phase.

In the system under consideration there are 5 substances: SAO, SASO3, B3, CO2, B and some of them are involved in the same reaction. These substances are distributed in four phases: CAO, SASO3, B3, the gas phase, each of which is characterized by the values \u200b\u200bof various properties inherent in it and is separated from other phases visible (at least under the microscope) the boundary of the section. The fact that the phase B3 is presented, most likely, the multitude of dispersed particles will not change the analysis - all particles are almost the same by properties and can be considered as one phase. The external pressure is constantly, therefore only one external variable remains - the temperature. Thus, all the terms for calculating the number of degrees of freedom ( from) Defined: from = (5 – 1) + 1 – 4 = 1.

The resulting value means that when the temperature changes (one parameter), the system will move from one equilibrium state to another and the number and nature of the phase will not change. System status parameters will be changed: temperature and equilibrium carbon dioxide and neutral gas pressure ( T. , P CO2 , R B.).

Strictly speaking, said rightly not for any temperatures below the temperature stop, but only for the interval when the reaction originally happening in the kinetic mode has passed into thermal regime and it is possible to really talk about the proximity of the system parameters to the equilibrium. At lower temperatures, the system is not significantly equilibrium, but on the character of the dependence of the temperature of the sample on time, this features are not reflected.

From the very beginning of the experiment - at room temperature, the system is in a state of equilibrium, but only because there are no substances that could interact. This refers to calcium oxide, which under these conditions (the partial pressure of carbon dioxide in the atmosphere of about 310 -4-atm, equilibrium pressure - 10 -23 atm) could carbonise. According to the isotherm equation for the reaction recorded taking into account the expression of the equilibrium constant (16.1) in the activities of condensed substances equal to one:

the change in the energy of Gibbs is positive, which means that the reaction should occur in the opposite direction, but this is not possible, since the system initially does not have calcium oxide.

With increasing temperature, the elasticity of dissociation (equilibrium CO2 pressure over carbonate is growing, as follows from the Isobara equation:

since the thermal effect of the reaction is greater than zero.

Only at a temperature of about 520 with the dissociation reaction will be thermodynamically possible, but it will begin with a significant delay in time (the incubation period) necessary for the nucleation of the oxide phase. Initially, the reaction will occur in the kinetic mode, but, at the expense of autocatalysis, the resistance of the kinetic stage will rather quickly decrease so much that the reaction will switch to thermal regime. It is from this moment that it becomes a fair thermodynamic analysis given above, and the sample temperature will begin to lag from the temperature of the hypothetical comparison sample, in which dissociation does not occur (see Figure 3).

The considered thermodynamic analysis will remain fair to the moment when dissociation elasticity reaches 1 atm. At the same time, carbon dioxide was continuously released on the sample surface of 1 atm. He penshes the air, and new portions come from the sample to replace it. The pressure of carbon dioxide will increase over one atmosphere, as gas freely goes into the surrounding atmosphere.

The system is fundamentally changing, because in the gas phase around the sample now there is no air and the system has become one component less. The number of degrees of freedom in such a system C \u003d (4 - 1) + 1 - 4 \u003d 0

it turns out to be zero, and when the equilibrium is maintained, no state parameters cannot change in it, including temperature.

Note now that all conclusions (calculation of the number of degrees of freedom, etc.) will remain fair, if not to take into account the component B3, which an unit increases the number of substances and the number of phases, which is mutually compensated.

There is a temperature stop when all incoming heat is consumed only on the dissociation process. The system works as a very good temperature control, when a small random change will lead to the opposite change in the dissociation rate, which returns the temperature to the previous value. High quality control is explained by the fact that such a system is practically irregular.

As the dissociation process is developed, the reaction front shifts the sample deep into the surface of the interaction and the thickness of the solid reaction product increases, which makes it difficult to diffusion of carbon dioxide from the reaction to the surface of the sample. From some time in time, the thermal mode of the process goes into a mixed, and then into diffusion. Already in mixed mode, the system will become substantially nonequilibrium and the conclusions obtained during thermodynamic analysis will lose their practical meaning.

Due to the reduction of the speed of the dissociation process, the required amount of heat will decrease so much that a part of the incoming heat flux will again begin to spend on the heating of the system. From this point on, the temperature stop will cease, although the dissociation process will still continue until a complete decomposition of carbonate.

It is not difficult to guess that for the simplest case in question, the value of the stop temperature can be found from the equation

The thermodynamic calculation according to this equation using the TDHT database gives the temperature of 883 ° C for pure calcite, and for pure aragonite - 834 ° C.

Now complicate the analysis. In the dissociation of calcite containing the impurities of the 1st and 2nd type, when the activity of carbonate and oxide cannot be considered equal to one, the corresponding condition will complicate:

If we assume that the impurity content is small and the resulting solutions can be considered as infinitely diluted, then the last equation can be written as:

where is the molar proportion of the appropriate impurity.

If an inclined temperatureplace and both temperatures are obtained ( T. 2 > T. 1) above stop temperature for pure calcium carbonate - To R. (T. 1)\u003e 1 and To R. (T. 2)\u003e 1, it is reasonable to assume that there are no second type impurities, or do not have time to dissolve () and evaluate the concentration of 1-type impurities at the beginning

and at the end of the temperature stop

A mixture of the first type should accumulate to a solution in a solution of SAS3 - B1 as the reaction front is moving. At the same time, the corner factor of the platform is expressed by the ratio:

where 1 is the proportion of the component B1 returning to the initial phase when it is in its pure form; V S. - molar volume of calcite; V C. - Dissociation rate of carbonate; - the thermal effect of the dissociation reaction at the stop temperature; R. 0 - the initial radius of calcite particles.

Attracting reference data, this formula can be calculated v C. - the velocity

rhenium component B1 in calcite.

2.4.2 Installation scheme and work technique

The work is studied by the dissociation of calcium carbonate and dolomite of various fractions.

The experimental installation scheme is shown in Figure 4.

Figure 4 - Installation scheme for studying the thermograms of the dissociation of carbonates:

1 - Corundum tube, 2 - carbonate, 3 - thermocouple, 4 - oven,

5 - autotransformer, 6 - Personal computer with ADC board

In a previously heated to 1200 to the furnace (4), a corundum tube (1) with a thermocouple (3) and a test calcium carbonate (2) was installed. A sample thermogram is observed on the monitor screen of the personal computer. After passing the isothermal section, experience with another carbonate fraction is repeated. In the study of dolomite, heating leads to the detection of two temperature stops.

The resulting thermograms are in the chart "Temperature - Time". For convenience of mapping, all thermograms must be brought on one chart. It determine the temperature of the intensive development of the process, compare it with found from thermodynamic analysis. Make conclusions about the effect of temperature, carbonate nature, degree of its dispersion on the character of the thermogram.

2.4.3 Processing and presentation of measurement results

According to the results of the work, you should fill out the following table:

Table 1. Results of the study of the calcium carbonate dissociation process (dolomite)

The first two columns are filled with values \u200b\u200bwhen opening the data file, the latter should be calculated. Smoothing is performed at five points, numerical differentiation of smoothed data is performed with additional smoothing, too, five points. Based on the results of the work, two separate dependency charts should be constructed: t. - and D. t. / D - t. .

The resulting temperature stop value ( T S.) It should be compared with a characteristic value for pure calcite. If the observed value is higher, then it is possible to approximately estimate the minimum content of the first type impurity by equation (16.7), believing that there are no second-type impurities. If the reverse relationship is observed, then we can conclude that the basic influence is the impurities of the second type and estimate their minimum content under the condition that there are no impurities of the first type. From equation (16.6) it follows that in the latter case

The value of the equilibrium constant is desirable to calculate using the TDHT database according to the method described in the manual. In the extreme case, you can use the equation that approximating the dependence of the Gibbs energy change in the calcium carbonate dissociation response with temperature:

G. 0 = B. 0 + B. one · T. + B. 2 · T. 2 ,

taking the values \u200b\u200bof the coefficients equal: B. 0 \u003d 177820, J / mol; B. 1 \u003d -162.61, J / (mol · k) B. 3 \u003d 0.00765, J · Mol -1 · K -2.

Note . If, in the course "Physical Chemistry", students are not familiar with the TDHT database and did not fulfill the appropriate calculations in practical classes, then the Schwartzman-Temkin equation and data from the reference book should be used.

Procedure for processing results

1. Enter the results of manual information record to the spreadsheet file.

2. Perform the smoothing of temperature values.

3. Build on a separate sheet a graph of temperature dependence on time.

4. Differentiation of temperature values \u200b\u200bin time with smoothing from 5 points.

5. Build on a separate sheet a graph of the dependence of the temperature derivative in time on temperature, determine the characteristics of the platforms.

Counting results:

1. In the book of the spreadsheet presented for verification, the following information should be presented on the first page with the name "Results":

a. In the cell "A1" - the value of the temperature stop (average for the inclined site), in the cell "B1" - units of measurement;

b. In the cell "A2" - the duration of the temperature stop, in the cell "B2" - units of measurement;

c. In the cell "A3" - the slope of the site, in the cell "B3" - units of measurement;

d. In the cell "A4" - the type of impurity or "0", if the presence of impurities was not detected;

e. In the cell "A5" - a molar fraction of impurities;

f. Starting from the cell "A7" should clearly formulate conclusions for work.

In cells A1, A3 and A5, there must be references to cells on other sheets of the book of spreadsheets on which calculations are made to obtain the result presented, and not the numeric values \u200b\u200bthemselves! If this requirement is not fulfilled, the verification program gives the message "information presentation error".

2. Properly decorated graphs of temperature dependences on time, temperature derivative in time from temperature and temperature derivative in time on separate sheets of spreadsheets with all the necessary signatures and notation.

3. Values \u200b\u200bof estimates of stop temperatures and their duration.

4. Conclusions for work.

Control questions

1. What depends on the temperature of the start of the air carbonate dissociation?

2. Why is the elasticity of the dissociation of carbonites grow with increasing temperature?

3. What is equal to the number of degrees of freedom of the system in which the balance between the CaO substances, CO 2, CASSO 3 has established?

4. How will the character of the thermogram change, if the dissociation product forms solid solutions with the source substance?

5. What mode of heterogeneous carbonate dissociation reaction is the isothermal area of \u200b\u200bthe thermogram?

6. How will the type of thermogram change during the dissociation of polydisperse carbonate?

7. What is the difference between the thermograms obtained at a general pressure of 101.3 kPa and 50 kPa?

2.5 Studying the temperature dependence of the viscosity of oxide melts (work number 17)

2.5.1 The nature of the viscous resistance of oxide melts

Viscosity is one of the most important physicochemical characteristics of slag melts. It has a significant effect on the diffusion mobility of ions, and hence, on the kinetics of the interaction of metal with slag, the speed of heat and mass exchange processes in metallurgical units. The study of the temperature dependence of viscosity gives indirect information on structural transformations in oxide melts, changes in the parameters of complex anions. The composition, which means, the value of viscosity depend on the purpose of the slag. For example, for the intensification of diffusion stages of the redox reducing interaction of the metal and slag (desulfuraction, dephosphoriation, etc.), the composition of the slag is chosen so that its viscosity is small. On the contrary, in order to prevent the transfer of hydrogen or nitrogen into steel through the slag from the gas phase, a slag with increased viscosity is added.

One of the quantitative characteristics of viscosity can be a dynamic viscosity coefficient (η), which is defined as the proportionality coefficient in Newton's internal friction law

where F. - Internal friction force between two adjacent liquid layers, Grad υ – Speed \u200b\u200bgradient S. - Surface surface of the contact of the layers. Unit of measurement of dynamic viscosity in C: [η] \u003d N · C / m 2 \u003d Pa · s.

It is known that the flow of fluid is a series of particle robes in the next steady position. The process is activated. To carry out the jumps, the particle must have a sufficient stock of energy compared to the average value. Excess energy is necessary for the breaking of chemical bonds of the moving particle and education in the volume of the vacancy melt (cavity) in which it passes. With increasing temperature, the average particle energy increases and their greater number can participate in the flow, which leads to a decrease in viscosity. The number of such "active" particles grows with a temperature according to the exponential law of the Boltzmann distribution. Accordingly, the dependence of the viscosity coefficient on temperature has an exponential view.

where η 0 is a coefficient, a little temperature-dependent, E. η - the activation energy of a viscous flow. It characterizes the minimum reserve of kinetic energy praying for active particles capable of participating during.

The structure of oxide melts has a significant effect on the viscosity coefficient. In contrast to the movement of ions under the action of an electric field, with a viscous course, all particles of fluid move in the direction of motion sequentially. The most accelerated step is the movement of large particles that give the greatest contribution to the value of η. As a result, the activation energy of a viscous flow, it turns out to be more so for electrical conductivity ( E. η > E.).

In acidic slags containing oxides Si, P, B, the concentration of large complex anions in the form of chains, rings, tetrahedra and other spatial structures (for example,

Etc.). The presence of large particles increases the viscosity of the melt, because Their movement requires high energy costs compared with small.

Supplements of the main oxides (CAO, MGO, MNO) lead to an increase in the concentration of simple cations (Ca 2+, Mg 2+, Mn 2+) in the melt. Inserted anions about 2- contribute to the depolymerization of the melt, i.e. decay of complex anions, for example,

As a result, the viscosity of slag decreases.

Depending on the temperature and composition, the viscosity of metallurgical slags may vary in fairly wide limits (0.01 - 1 Pa · c). These values \u200b\u200bon the orders of magnitude exceed the viscosity of liquid metals, which is due to the presence in the slags of relatively large modes of flow.

The reduced exponential dependence of η from T. (17.2) It is not bad to describe experimental data for the main slags containing less than 35 mol. % SIO 2. In such melts, the activation energy of viscous flow E. η is constant and has a small amount (45 - 80 kJ / mol). If the temperature decreases, η changes, slightly and only when hardening, starts intensively increase.

In acidic slags having a high concentration of complex-forming components, activation energy can decrease with increasing temperature: E. η = E. 0 / T. What is caused by the disagreement of complex anions when heated. Experimental data in this case are linearized in the coordinates " lN. η - 1 / T. 2.

2.5.2 Description of installation and methods for measuring viscosity

To measure the viscosity coefficient, a rotary viscometer is used (Figure 5). The device and the principle of operation of this device is as follows. The cylindrical cylindrical cylindrical (1) is placed (2), which immerses spindle (4), suspended on an elastic string (5). During the experience, the rotational moment from the electric motor (9) is transmitted to the disk (7), from it through the string of the spindle.

The magnitude of the viscosity of the oxide melt is judged by the angle of twisting the string, which is determined on the scale (8). When rotating, the spindle is a viscous resistance of the fluid creates the thrust moment of the force that twists the string until the moment of the elastic deformation of the string becomes an equal moment of the forces of viscous resistance. At the same time, the speed of rotation of the disk and the spindle will be the same. Corresponding to this state, the angle of twisting the string (Δφ) can be measured by comparing the position of the arrow (10) relative to the scale: initial - before turning on the electric motor and the installed - after switching on. Obviously, the angle of twisting the string Δφ is the greater, the greater the viscosity of the liquid η. If string deformations do not exceed the limit (appropriate feasibility of the bike law), then the value of Δφ is proportional to η and can be written:

Coefficient equation k. The name of the constant viscometer depends on the size of the crucible and spindle, as well as from the elastic properties of the string. With a decrease in the diameter of the string, the sensitivity of the viscometer increases.

Figure 5 - Installation scheme for viscosity measurement:

1 - Tigel, 2 - The test melt, 3 - spindle head,

4 - spindle, 5 - string, 6 - upper installation, 7 - disk,

8 - scale, 9 - electric motor, 10 - arrow, 11 - oven, 12 - transformer,

13 - Temperature adjustment device, 14 - thermocouple.

To determine a constant viscometer k. A liquid with a known viscosity is placed in the crucible - a solution of rosin in transformer oil. In this case, in the experiment at room temperature, Δφ0 is determined. Then, knowing the viscosity (η0) of the reference fluid at a given temperature, calculate k. according to the formula:

Found value k. Used to calculate the viscosity coefficient of the oxide melt.

2.5.3 Working procedure

For acquaintance with the viscosity properties of metallurgical slags in this laboratory work, the melt of Na 2 O · 2B 2 O 3 is studied. Measurements are carried out in the temperature range of 850-750 o C. After reaching the initial temperature (850 ° C), the viscometer arrow is installed on a zero mark. Then includes an electric motor and fix the stationary angle of twisting the string Δφ t . HE Turning off the viscometer, repeat the measurement Δφ t with other temperatures. Experience is stopped when the angle of string will begin to exceed 720 o.

2.5.4 Processing and presentation of measurement results

According to the measurement results, the following table is filled.

Table 1. Temperature dependence of viscosity

In the table, the first two columns are filled from the results of manual recording of temperature tests on the monitor screen and thread spinning angle over the scale of the viscometer. The remaining columns are calculated.

To verify the feasibility of the exponential law of changes in the viscosity coefficient with a temperature (17.2) build a schedule in the coordinates "LN (η) - 10 3 / T. " The activation energy is found using the LINEST (OPENOFFICE.CALC) or LINEIN () (MicrosoftOffice.exel), using them to the fifth and sixth columns of the table.

In the conclusions, the obtained data of η and E η are compared with known for metallurgical slags, discusses the nature of the temperature dependence of viscosity, its connection with structural changes in the melt.

Procedure for processing results

1. Conduct measurements on the calibration cell and calculate the permanent installation

2. Enter the results of manual information record to the spreadsheet file.

3. Calculate viscosity values.

4. Build on a separate sheet a graph of viscosity dependence on temperature.

5. Calculate the logarithm of viscosity and the inverse absolute temperature for the entire set of measurement results.

6. Find the least squares method coefficients b. 0 , b. 1 equations, approximating the dependence of the logarithm of viscosity from the inverse temperature, and calculate the activation energy.

7. Build on a separate sheet a graph of viscosity logarithm dependence on the inverse temperature and bring an approximating dependence Counting results:

1. In the book of the spreadsheet presented for verification, the following information should be presented on the first page with the name "Results":

a. In the cell "A1" -Close temperature, in the cell "B1" - units of measurement;

b. In the cell "A2" - the final temperature, in the cell "B2" - units of measurement;

c. In the cell "A3" - the activation energy of a viscous flow at low temperatures, in the cell "B3" - units of measurement;

d. In the cell "A4" - a pre-exponential factor in the formula of the temperature dependence of electrical conductivity at low temperatures, in the cell "B4" - units of measurement;

e. In the cell "A5" - the activation energy of a viscous flow at high temperatures, in the cell "B5" - units of measurement;

f. In the cell "A6" - a pre-exponential factor in the formula for the temperature dependence of electrical conductivity at high temperatures, in the cell "B6" - units of measurement;

g. Starting from the cell "A7" should clearly formulate conclusions for work.

In the A1-A6 cells, there must be references to cells on other sheets of the book of spreadsheets on which calculations are made to obtain the result presented, and not the numeric values \u200b\u200bthemselves! If this requirement is not fulfilled, the verification program gives the message "information presentation error".

2. Properly decorated graphs of viscosity dependences on the temperature and logarithm of viscosity from the inverse temperature obtained according to the experimental data (points) and the approximated polynomial (line), on separate sheets of spreadsheets with all the necessary signatures. Control questions

1. In what form are the components of the oxide melt, consisting of CAO, Na 2 O, SiO 2, B 2 O 3, Al 2 O 3?

2. What is called the viscosity coefficient?

3. How will the temperature dependence of the slag viscosity change when the main oxides add to it?

4. In which units is the viscosity?

5. How do the constant viscometer determine?

6. What is determined by the activation energy of a viscous flow?

7. What is the reason for reducing viscosity with increasing temperature?

8. How to calculate the activation energy of a viscous flow?

2.6 Restoration of manganese from oxide melt in steel

(Work number 18)

2.6.1 General laws of electrochemical interaction of metal and slag

The processes of interaction of the liquid metal with the molten slag have a large technical value and proceed in many metallurgical units. The performance of these aggregates, as well as the quality of the finished metal is largely determined by the speed and completeness of the transition of certain elements across the border of the phases.

The simultaneous flow of a significant number of physical and chemical processes in various phases, high temperatures, the presence of hydrodynamic and heat fluxes make it difficult to experimental study of the phase interaction processes in industrial and laboratory conditions. Such complex systems are investigated using models that reflect individual, but the most essential aspect of the object under consideration. In this paper, the mathematical model of the processes occurring on the border of the metal - slag allows you to analyze the change in the volume concentrations of components and the speed of their transition through the interfacial border depending on the time.

Restoration of manganese from oxide melt occurs on electrochemical semi-resource:

(Mn 2+) + 2e \u003d

Related processes must be oxidation processes. Obviously, it can be the process of iron oxidation

\u003d (Fe2 +) + 2e

or impurities in the composition of steel, for example, silicon. Since the four-charged silicon ion can not be in a slag. This process is accompanied by the formation of a silicial tetrahedron in accordance with the electrochemical half-formation:

4 (O 2-) \u003d (SiO 4 4-) + 4e

Independent flow of only one of the shown electrode semedies is impossible, because This leads to accumulation of charges in a double electric layer on the border of the phase separation that prevents the transition of the substance.

The state of equilibrium for each of them is characterized by the equilibrium electrode potential ()

where is the standard potential - the activity of the oxidized and reduced forms of the substance, z. - the number of electrons involved in the electrode process, R. - universal gas constant, F. - Permanent Faraday T. - temperature.

The restoration of manganese from slag to the metal is realized as a result of the joint flow of at least two electrode semi-resources. The speeds are established so that chargements on the interfacial border do not occur. In this case, the metal potential takes a stationary value in which the speed of generation and assimilation of electrons is the same. The difference between the actual, i.e. Inpatient, potential and its equilibrium value, is called polarization (overvoltage) of the electrode ,. Polarization characterizes the degree of removal of the system from equilibrium and determines the rate of transition of components across the border of the phases in accordance with the laws of electrochemical kinetics.

From the standpoint of classical thermodynamics in the system in one direction or another, the processes of recovery of manganese from the slag dissolved in the silicon gland are occurring:

2 (MNO) + \u003d 2 + (SiO 2) H \u003d -590 kJ / mol

and solvent ourselves (oxidation of manganese iron oxide in slag

(MNO) + \u003d + (FEO) \u003d. H \u003d 128 kJ / mole

From the standpoint of formal kinetics, the rate of the first reaction, which is determined, for example, by changing the silicon content in the metal, away from equilibrium in kinetic mode should depend on the product of the concentrations of manganese oxide in slag and silicon in metal in some degrees. In diffusion mode, the reaction rate should linearly depend on the component concentration, the diffusion of which is difficult. Similar arguments can be made in relation to the second reaction.

Equilibrium Constant Reaction, expressed through activity

it is function only temperature.

The ratio of equilibrium concentrations of manganese in slag and metal

they are called the coefficient of the distribution of manganese, which, in contrast to depends on the composition of the phases and serves as a quantitative characteristic of the distribution of this element between slag and metal.

2.6.2 Process model

The simulation model examined three electrode semoretakes that can flow between the CaO oxide melt - MnO - Feo - SiO 2 - Al 2 O 3 and the liquid iron containing Mn and Si as impurities. The assumption of the diffusion mode of their flow is done. The diffusion of FE 2+ particles in a slag, silicon in metal, manganese in both phases is taken into account. The overall system of equations describing the model has the form

where υ ј - speed of electrode semi-reaction, η J. - polarization, i J. - the density of the limit current of diffusion, D J. - diffusion coefficient, β - convective constant, C j. - Concentration.

The program of the simulation model allows you to solve the system of equations (18.4) - (18.8), which makes it possible to establish how the volume concentration of components and the speed of their transition changes with time when the metal interacts with the slag. The calculation results are displayed. The information obtained from the monitor screen includes a graphic image of changing the concentrations of the main components, their current values, as well as temperature values \u200b\u200band constructions of convection (Figure 8).

The block diagram of the program of the simulation model of the interaction of metal and slag is presented in Figure 7. The program operates in a cycle, which is terminated only after the specified modeling time (approximately 10 minutes).

Figure 7 - block diagram of the program of the simulation model

2.6.3 Working procedure

The image generated by the simulation program is represented in Figure 8 (right panel). In the top of the panel, selective numeric values \u200b\u200bof the measured values \u200b\u200bare given, the graph shows all the values \u200b\u200bobtained during the process modeling. In the notation of the components of metallic and slag melts, the metallurgical topics received additional signs are used. Square brackets indicate the belonging of the component with a metal melt, and round-slag. Multipliers for the designations of components are used only to build a schedule, they should not be taken into account when interpreting values. During the model operation, only the value of one of the measured values \u200b\u200bis displayed. After 6 seconds it disappears and the value of the next magnitude appears. During this period of time, you have to have time to record the next value. For time saving, it is recommended that the constant numbers are not recorded, for example, the leading unit in the temperature value.

Figure 8. Image of the monitor screen when performing work number 18 at different stages of processes.

Four to five minutes after starting the installation, make an additive of the previously warm manganese oxide into the slag, which is implemented while pressing the ALT key and the numeric keys on the main keyboard with your installation number. Processing procedure:

1. Enter the results of manual information record to the spreadsheet file.

2. Calculate the speed of the processes of the transition of elements through the interfacial boundary and the logarithm of these values \u200b\u200bbefore and after the addition of manganese oxide into the slag with a mass of the metal melt of 1400 kg.

3. Build on separate sheets of graphics of temperature dependence on time, manganese transition speeds from time to time, the logarithm of the transition speed of silicon from the logarithm of silicon concentrations in the metal.

4. The smallest square method to estimate the kinetic characteristics of the silicon transition process.

Counting results:

1. Properly decorated graphs listed in the previous section on a separate sheet of spreadsheets with all the necessary signatures and notation.

2. The values \u200b\u200bof the order of silicon oxidation reaction before and after the administration of manganese oxide indicating the errors.

3. Conclusions for work.

Control questions

1. Why does the need to simulate steel production processes?

2. What is the nature of the interaction of metal with slag and what does this manifest themselves?

3. What potential is it called stationary?

4. What potential is called equilibrium?

5. What is called electrode polarization (overvoltage)?

6. What's called manganese distribution coefficient between metal and slag?

7. What depends on the constant of the distribution of manganese between the metal and slag?

8. What factors affect the transition rate of manganese from metal into the slag in diffusion mode?

Bibliography

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5. Lepinsky, B.M. Transport properties of metal and slag melts [text]: Reference / B.M. Lepinsky, A.A. Belousov / under. ed. Watolina N.A. - M.: Metallurgy, 1995. - 649 p.

6. Belous, G.E. Organization of Metallurgical Experiment [Text]: Tutorial / G. Bela, V.V. Debovsky, O.V. Something. - M.: Chemistry, 1982. - 228 p.

7. Panfilov, A.M. Calculation of thermodynamic properties at high temperatures [Electronic resource]: educational and methodological manual for students of metallurgical and physicotechnical faculties of all forms of learning / A.M. Panfilov, N.S. Semenova - Ekaterinburg: USTU-UPI, 2009. - 33 c.

8. Panfilov, A.M. Thermodynamic calculations in EXCEL spreadsheets [Electronic resource]: Methodical instructions for students of metallurgical and physico-technical faculties of all forms of learning / A.M.Panfilov, N.S. Semenova - Yekaterinburg: Ugta, 2009. - 31 s.

9. Brief reference book of physico-chemical values \u200b\u200b/ under. ed. A.A. Tallee and A.M. Ponomareva. L.: Chemistry, 1983. - 232 p.

and solvent ourselves (oxidation of manganese iron oxide in slag

(MNO) + \u003d + (FEO) \u003d. H \u003d 128 kJ / mole

Equilibrium Constant Reaction, expressed through activity

it is function only temperature.

The ratio of equilibrium concentrations of manganese in slag and metal

2.6.2 Process model

(18.4)

Figure 7 - block diagram of the program of the simulation model

2.6.3 Working procedure

Figure 8. Image of the monitor screen when performing work number 18 at different stages of processes.

1. Enter the results of manual information record to the spreadsheet file.

4. The smallest square method to estimate the kinetic characteristics of the silicon transition process.

Counting results:

1. Properly decorated graphs listed in the previous section on a separate sheet of spreadsheets with all the necessary signatures and notation.

2. The values \u200b\u200bof the order of silicon oxidation reaction before and after the administration of manganese oxide indicating the errors.

3. Conclusions for work.

Control questions

1. Why does the need to simulate steel production processes?

2. What is the nature of the interaction of metal with slag and what does this manifest themselves?

3. What potential is it called stationary?

4. What potential is called equilibrium?

5. What is called electrode polarization (overvoltage)?

6. What's called manganese distribution coefficient between metal and slag?

7. What depends on the constant of the distribution of manganese between the metal and slag?

8. What factors affect the transition rate of manganese from metal into the slag in diffusion mode?

Bibliography

1. Lynchevsky, B.V. Metallurgical Experiment Technique [Text] / B.V. Lynchevsky. - M.: Metallurgy, 1992. - 240 p.

3. Popel, S.I. The interaction of the molten metal with gas and slag [text]: Tutorial / S.I. Popel, Yu.P. Nikitin, L.A. Barmin et al. - Sverdlovsk: ed. Upi them. CM. Kirov, 1975, - 184 p.

4. Popel, S.I. The theory of metallurgical processes [Text]: Tutorial / S.I. Popel, A.I. Sotnikov, V.N. Boronenkov. - M.: Metallurgy, 1986. - 463 p.

5. Lepinsky, B.M. Transport properties of metal and slag melts [text]: Reference / B.M. Lepinsky, A.A. Belousov / under. ed. Watolina N.A. - M.: Metallurgy, 1995. - 649 p.

6. Belous, G.E. Organization of Metallurgical Experiment [Text]: Tutorial / G. Bela, V.V. Debovsky, O.V. Something. - M.: Chemistry, 1982. - 228 p.

9. Brief reference book of physico-chemical values \u200b\u200b/ under. ed. A.A. Tallee and A.M. Ponomareva. L.: Chemistry, 1983. - 232 p.

Ministry of Education and Science of the Russian Federation

Federal Agency for Education

South Ural State University

Branch in Zlatoust

Department of "General Metallurgy"

669. 02/ . 09 (07)

D463.

Theory of metallurgical processes

Tutorial

Chelyabinsk

Publishing House of Jurag.

Introduction

Metallurgical processes are a combination of physical phenomena and physicochemical transformations (movement of gases, liquid and solid materials, heat and mass exchange, phase transitions, oxidation and restoration of materials, etc.) occurring in metallurgical units (blast furnace, agglomerating machine , steel-smelting and heating furnace, converter) at high temperatures. The subject of studying the course "Theory of Metallurgical Processes" are reactions occurring in these metallurgical units.

The TMP course occupies a special position among all metallurgical disciplines, in fact, it is applied physical chemistry in relation to the analysis of phenomena occurring in the production of cast iron, steel and ferroalloys.

The theoretical bases of metallurgical processes are considered in a certain sequence: initially, on the basis of the laws of thermodynamics, the conditions of the equilibrium of chemical processes are analyzed, then the kinetics and features of the processes mechanism. These questions are the main tasks deciding when studying the TMP course.

1. The composition and properties of high-temperature gas Atmosphere

1.1. Gas atmospheric thermodynamics

The pyrometallurgical processes of production of metallurgical melts (cast iron, steel, alloy) occur with the participation of gas atmospheres, which may be neutral, oxidative and reducing.

The composition, pressure and temperature of the gas phase depend on the nature of its interaction with other phases formed during the preparation of metals and alloys. At the same time, both intermediate and the full composition of the gas phase is very similar:

products of complete interaction of oxygen elements - CO2, H2O (pairs), SO3;

incomplete interaction products with oxygen, dissociation of oxides and degassing metals - CO, SO2, H2, O2, N2, CH4; Inert gases - Ar, Kr.

The equilibrium composition of the gas phase can be calculated based on the thermodynamic analysis of chemical reactions, the most important of which are reactions of interaction with hydrogen oxygen, carbon monoxide, methane and sulfur arhydride.

These reversible reactions are described by the following chemical equations (1 mol of O2):

2H2 + O2 \u003d 2H2O (pairs),	J;
2 o + O2 \u003d 2SO2,	J;
2Sh4 + O2 \u003d 2 + 4H2O,	J;
1 / 2SH4 + O2 \u003d 1 / 2CO2 + H2O,	J;	(1.4)
2SO2 + O2 \u003d 2SO3,	J.

The thermodynamic analysis of reversible reaction data allows you to establish equilibrium content and partial pressure of molecular oxygen, as well as characterize the redox properties of the gas phase in the indicated reactions.

However, a more important thermodynamic characteristic that determines the direction of flowing chemical reactions is to change the power of Gibbs D GT, the standard change of which D G ° T, depending on the temperature for reactions (1.1) - (1.5) has the appearance, J:

D g ° (1.1) \u003d - + 108 t;

D g ° (1.2) \u003d - + 175 t;

D g ° (1.3) \u003d - + 370 t;

D g ° (1.4) \u003d - + 2 t;

D G ° (1.5) \u003d - + 196 T.

In fig. 1.1 Presented graphs of these dependencies.

Fig. 1.1. Standard Gibbs Energy for Burning Reactions

These dependences are valid at temperatures up to 2500 K and the general pressure in the system P \u003d 1 atm., I.e., to the dissociation processes H2O, O2, H2 on atoms, their ionization and plasma formation.

From the analysis of the reduced dependences and graphs of the form D G ° T \u003d F (T) in Fig. 1.1 It follows that with an increase in pressure equilibrium of reactions (1.1), (1.2) and (1.5) shifts in the forward direction, and with an increase in the temperature of the completeness of these reactions decreases. The change in pressure does not affect the reaction equilibrium (1.4), and the direct course of the reaction (1.3) is slowed down with an increase in pressure. With an increase in the reaction temperature (1.3) and (1.4) are characterized by greater complete flow.

The equilibrium composition of the formed atmosphere and the partial pressure of its components of the components will determine and calculate the redox properties (ABS) of the gas phase affecting the materials of the heterogeneous system capable of oxidation or restoration.

The simplest quantitative characteristic of any gas mixture is the equilibrium partial pressure of oxygen. However, a more accurate estimate of the oats of the gas atmosphere is its oxygen potential P O, which is the value of the chemical potential of molecular oxygen when it counts from the standard state, in which Div_Adblock144 "\u003e

The value P is depends on the temperature and on the composition of the gas phase, which is expressed through the ratio of partial pressures of reagents affecting.

In metallurgical units, gas atmospheres consist of a variety of components that are constantly involved in physicochemical transformations. Thermodynamic analysis of such systems is based on approval that complex chemical equilibrium is achieved as a result of simultaneous establishment in the system of all possible private equilibrium.

So, while simultaneously flowing in the gas phase of reactions (1.1) - (1.5) at T \u003d const Pressure of these components, the values \u200b\u200bcorresponding to the equilibrium constants of the Kyrgyz Republic (1.1) -KR (1.5), and the oxygen potential of the gas mixture

can be calculated according to data from any of these equilibriums, for example, by equation

In the octhomecomponent gas mixture under consideration, in addition to reactions (1.1) - (1.5), other chemical interactions between reagents are also possible. The so-called water gas reaction is the greatest interest (water gas is called a mixture of four gases H2 - H2O - CO2):

H2 + CO2 \u003d H2O + CO, D G ° (1.5) \u003d - 33,5t J. (1.8)

Analysis of this reaction is extremely important in metallurgy to estimate equilibrium in gas atmospheres when using natural gas or a moistened blast in a blast furnace, other metallurgical units.

To determine the equilibrium composition of the reaction system (1.8), it is necessary to be specified not only by the value of the equilibrium constant

(1.9)

and general pressure

(1.10)

but also two other terms that follows from the analysis of the number of degrees of freedom:

C \u003d P + 2 - F \u003d 3 + 2 - 1 \u003d 4.

In practice, the initial composition of the system or partial pressure of vapors in the initial mixture is most often set. In our case, in addition to the number of two variables, you can choose not changing numbers of carbon and hydrogen moles or non-varying amounts of partial pressure of hydrogen and carbon-containing gases:

(1.11)

(1.12)

The joint solution of equations (1.9) - (1.12) allows you to find the equilibrium composition of the gas mixture. The results of calculations can be represented graphically, with the initial data are relations:

(1.13)

From the graph (Fig. 1..gif "width \u003d" 69 "height \u003d" 28 "\u003e and vice versa. After calculating the equilibrium value of% Co /% CO2 (or% H2 /% H2O), it is possible to determine the oxygen potential of the CO2 system. H2 - H2O and apply in Fig. 1.2 Lines of permanent values \u200b\u200bP O.

Fig. 1.2. The ratio between%/% CO2 and% H2 /% H2O.

1.2. Homogeneous gas processes

The thermodynamic analysis of reactions occurring in complex gas atmospheres allows only to judge the possibility of reaction flow in direct or reverse directions and calculate the composition of the gas phase. However, it is impossible to consider the mechanism of interaction processes and conduct their kinetic analysis.

The mechanism of interaction of valented saturated molecules should include a break or weakening of valence relations. This requires large energy costs, which cannot be compensated only by the energy of thermal motion of molecules. As experimental data shows, all combustion reactions have a chain mechanism characterized by the participation of active centers (particles) - atoms and radicals with free valences. The simplest acts of the multi-stage oxidation process begin after the formation of active centers and proceed as chemical reactions between them and molecules with small energy energy. A feature of such reactions is the reproduction of active centers. By the nature of its flow, chain reactions are divided into unbranched, branched and with degenerate branching.

In general, the model in the theory of chain reactions is the most studied reaction of hydrogen combustion, which is characterized by a small number of intermediate products and well-allocated elementary acts. They are:

1) the reaction of the formation of active centers in the volume of the mixture and on the vessel wall:

E1.14 \u003d 198.55 kJ / mol; (1.14)

E1.15 \u003d 180.7 kJ / mol; (1.15)

Supply + O2 \u003d N2; (1.16)

2) Circuit continuation reaction:

https://pandia.ru/text/79/398/images/image020_45.gif "width \u003d" 172 "height \u003d" 48 src \u003d "\u003e Е1.17 \u003d 41,9kj / mol; (1.17)

3) chain branching reactions:

E1.18 \u003d 63.27 kJ / mol; (1.18)

E1.19 \u003d 25.14 kJ / mol; (1.19)

4) Circuit break reaction (decontamination) on the wall

; (1.20)

5) Reaction of circuit breaks in the volume of the gas phase (M - neutral molecule):

E (1.21) "0; D H1.20 \u003d - 197 kJ / mol. (1.21)

The speed of each of these reactions is determined by the partial pressure P and the order of the reaction N and in general, it can be represented as

V \u003d const × https://pandia.ru/text/79/398/images/image029_30.gif "width \u003d" 411 height \u003d 267 "height \u003d" 267 "\u003e

Fig. 1.3. Gas mixture conditions (H2 + O2)

2. Analysis of solid carbon combustion processes

Of the possible carbon interactions with oxidants, consider the most important.

1. The reaction of incomplete carbon combustion

2C + O2 \u003d 2SO, D G ° T (2.1) \u003d - - 180T J / mol. (2.1)

2. Complete combustion reaction

C + O2 \u003d CO2, D G ° T (2.2) \u003d - - 2,3T J / mol. (2.2)

3. Carbon gasification reaction by steam H2O to

2C + 2N2O \u003d 2C + 2N2, D G ° T (2.3) \u003d - 288t J / mol. (2.3)

4. Carbon gasification reaction steam H2O to CO2

C + 2N2O \u003d CO2 + 2N2, D G ° T (2.4) \u003d - 110.6T J / mol. (2.4)

5. Carbon gasification reaction

C + CO2 \u003d 2SO, D G ° T (2.5) \u003d - 177.7T J / mol. (2.5)

The reaction (2.5) is the greatest interest, which is endothermic: D H ° \u003d 172.6 kJ.

With respect, which is established by the carbon gasification reaction, one can judge the effect of solid carbon on the composition of the gas phase of the C - CO2 system in a wide temperature range. The equilibrium composition of this gas atmosphere is presented in Fig. 2.1.

According to the principle of the lesser, the increase in pressure shifts the equilibrium of the carbon gasification reaction to the left, that is, at a constant temperature, the equilibrium gas mixture is enriched with CO2 dioxide. When the pressure decreases, the concentration of CO in the gas phase increases.

The heterogeneous process of carbon interaction with the oxidizer consists of a number of stages:

2) molecular diffusion through a hydrodynamic layer with a thickness of D, where the laminar flow is preserved;

3) the adsorption of the oxidant on the surface of the carbon;

4) chemical interaction with the formation of adsorbed products (CO2 at low temperatures and with high);

5) desorption of reaction products;

6) diffusion (molecular and turbulent) reaction products to the gas stream.

Fig. 2.1. The composition of the gas atmosphere (with- CO2) in equilibrium with solid carbon

Limiting in the process of carbon oxidation is the adsorption-kinetic stage, which combines stages 3, 4 and 5. The molecular diffusion may be limiting.

Diffusion rate per unit surface can be calculated by the formula

(2.6)

where D is the diffusion coefficient, b is the coefficient of mass transfer, CO and SPO - the concentration of the oxidant in the volume of the gas phase and on the carbon surface, respectively.

The speed of chemical interaction is determined by the concentration of the adsorbed reagent of the SPOV:

(2.7)

where K is the reaction rate constant, depending exponentially on the temperature of the activation energy of the process, N is the order of the reaction (in this case n \u003d 1).

If the process of carbon interaction with the gas phase occurs in stationary mode, i.e., without changing the speed in time, the speed of this process of the VPCC is defined as

Vprot \u003d V x. p \u003d Vd. (2.8)

Substituting in (2.8) relations (2.6) and (2.7), as a result, we obtain the observed speed of the carbon oxidation process:

(2.9)

Depending on the ratio of the values \u200b\u200bof K and B, the following oxidation modes are possible:

- kinetic at b \u003e\u003e k;

- diffusion at K \u003e\u003e B;

- diffusion-kinetic at k "b.

Thermodynamic analysis of the reaction (2.5) allows you to identify the conditions for the decay of carbon monoxide. This is possible in gas atmospheres with a high attitude and with a decrease in temperature. Value D G ° T for reaction

2CO \u003d CO2 + with

it decreases with a decrease in temperature, but kinetically without a catalyst to carry out this reaction used, for example, in the process of cementation, is difficult.

For the oxidation of the communication "C - O" in the molecule, you need a catalytic solid surface, the strongest catalyst is iron. At the same time, the main stages of the decay process of the CO with the formation of solid fine carbon will be the following:

1) adsorption of the CO molecule on the surface of the catalyst, leading to the illegibility of the communication "C - O";

2) the decay process when the active molecule is impaired from the gas phase about adsorbed by the reaction

CO + SUPS \u003d CO2 + S.

3. Evaluation of the strength of chemical compounds

The dissociation processes of the most important for metallurgy compounds - oxides, nitrides, carbonates are very important, since they are a direct method of producing metals. These processes are very similar, and depending on the temperature they can be represented by the equations of the form:

AUTV \u003d ATV + VGAZ;

AUTV \u003d already + VGAZ;

Aug \u003d ATV + VGAZ;

Aug \u003d Als + VGAZ.

The magnitude of the equilibrium partial pressure of the gaseous product of these reactions is called dissociation elasticity Connections AB and characterizes the strength of this connection. The dissociation reactions are endothermic, i.e., with an increase in temperature, the equilibrium is shifted towards the reaction products. Reducing the pressure while maintaining the composition of the gas phase has a similar effect.

According to the Gibbs phases rule, the number of freedom degrees for dissociation reactions is defined as

C \u003d K + 2 - F \u003d 2 + 2 - 3 \u003d 1,

i.e., for a quantitative characteristic, only one independent parameter is sufficient, from which the equilibrium constant depends:

Kr \u003d pv \u003d | (T).

Fig. 3.1. Dependence of the elasticity of dissociation of the compound av to temperature

In fig. 3.1 shows the dependence of the RV on temperature for the indicated reactions.

3.1. Dissociation Carbonate

In ferrous metallurgy, the greatest practical interest is the analysis of the dissociation of calcium calcium carbonates, MGCO3 magnesium, manganese Mnco3, FECO3 (Siderite) and Dolomite CAMG (CO3) 2. Dissociation processes of these compounds of the same type and proceed by equation:

MECO 3 \u003d MEO + CO 2,

The magnitude is the elasticity of the dissociation of carbonate and characterizes the measure of the chemical strength of the compound.

The most interest is the response of calcium carbonate, which is part of the charge materials of the domain and steelmaking production, and is also used to obtain SAO through limestone roasting.

The dissociation reaction of SASO3 is described by the view equation

SCO 3 \u003d CaO TV + CO 2, \u003d J; (3.1)

D G ° T \u003d - 150 t; KP (3.1) \u003d

The dependence of the resistance of the dissociation of carbonate on temperature is presented in Fig. 3.2.

Fig. 3.2. Elasticity of dissociation dissociation3.

Analysis of this graphic dependence using a chemical reaction isotherm shows that the carbonate dissociation is possible when the actual value of the equilibrium and at the same time D G ° T< 0. Температура, при которой возможен этот процесс, является температурой начала диссоциации ТНД.

Any figurative point 1 is higher than the equilibrium line in fig. 3.2 meets the sustainable existence of CASS3 carbonate. Any figurative point 2 below the line meets the sustainable existence of SAO oxide.

The process of the dissociation of carbonate proceeds at a high rate at temperatures above the temperature of the chemical boiling of TKC, at which the elasticity of dissociation becomes equal to the total external pressure of the gas phase.

3.2. Dissociation of iron oxides

The thermodynamics of oxide dissociation processes is similar to the process of dissociation of carbonates, features are associated only with the presence of various degrees of valence in some metals - in particular, iron oxides.

In accordance with the principle of Baikov, the dissociation of iron oxides occurs consistently, from the highest to the lowest up to the formation of metal. The dissociation reactions are as follows:

6Fe2O3 \u003d 4Fe3O4 + O2, D G ° T \u003d - 281.3 t J; (3.2)

2Fe3O4 \u003d 6Feo + O2, D G ° T \u003d - 250.2 t j; (3.3)

2Feo \u003d Fe + O2, D G ° T \u003d - 130.7 t j; (3.4)

1 / 2Fe 3O 4 \u003d 3 / 2Fe + O 2, D G ° T \u003d - 160.2 t J. (3.5)

These oxides exist in certain temperature intervals. In fig. 3.3 shows graphs of dependencies D G ° T on the reaction temperature (1) - (4).

Fig. 3.3. Standard Gibbs Energy Dissociation Reactions Iron Oxides

According to the calculated values \u200b\u200bof dissociation elasticity, dependencies were built Presented in Fig. 3.4.

Fig. 3.4. Areas of sustainable existence

iron and its oxides

On this diagram, the areas of the sustainable existence of pure iron and its oxides in a wide temperature range are indicated. The point O corresponds to an irony equilibrium with the parameters T \u003d 575 ° C and "- 26 (four phases are in equilibrium - solid Fe, FEO, FE3O4 and O2). On the rest of the lines, an unlikely equilibrium is being implemented. Any point between the lines corresponds to the fixed state of the bivariant system, which allows determining the conditions for the sustainable existence of this condensed phase.

3.3. Mechanism and kinetics of dissociation processes

Distinctive features of dissociation processes occurring by the reaction of the type

AUTV ® ATV + VGAZ,

are:

- the presence of the process of the nucleation of the new solid phase;

- localization of the process on the border of the "old" and "new" solid phases section;

- The dependence of the speed of the process on the degree of transformation.

The characteristics of such a process use the degree of transformationa:

where MAB (P), MAB (Ex) - The equilibrium and initial value of the AV connection.

The degree of transformationa. Depends on the time of the process, which is confirmed by numerous experimental data (Fig. 3.5).

font-Size: 13.0PT; Letter-Spacing: -. 1pt "\u003e Fig. 3.5. Isothermal dependence of the degree of transformationa. from time
and the speed of transformation on the degree of transformation

At the same time, three stages can be distinguished:

I - induction period characteristic of low speed rates due to the difficulties of the nucleation of a new phase;

II - autocatalysis associated with the acceleration of the dissociation reaction;

III - the period of completion of the process, which is associated with a decrease in the amount of the old phase and the surface of the section.

Experimental studies of dissociation processes indicate the flow of such a process according to the scheme

AUTV ® ATV × VGAZ (ADS) ® AtTan + VGAZ.

In this case, the formation of a new phase embryo in the depths of the old should be accompanied by a decrease in the energy of Gibbs system calculated by the equation

D G \u003d D GV + D GW,

where D GV and D GW are the volumetric and surface components of the overall change in Gibbs energy.

Values \u200b\u200bD GV and D GW are defined as

D gv \u003d.

D gw \u003d s × s,

where V and S are the volume and surface of the nucleus of the new phase, R and M is the density and molecular weight of the new phase, S is the surface tension, M 2 and M 1 - the chemical potentials of the AV connections in the new and old phase.

From the analysis of this relation, it follows that spontaneously the process of forming a new phase is possible with a certain ratio M 2 and M 1.

At T £ TND M 2 ³ M 1, and in this case the appearance of the embryo of any size is thermodynamically impossible.

If T\u003e TND, then M 2\u003e M 1, and the components in the DG formula have a different sign, because with the growth of R, the first term increases in absolute value faster, then the curve DG \u003d F (R) has a maximum, which determines The magnitude of the critical embryo, the growth of which is accompanied by a decrease in the energy of the system. Under some conditions, the germ of the new phase becomes thermodynamically stable. The degree of overheating of the compound of the AUTV determines both the radius of the critical embryo and its stability. To determine the size of the critical embryo, it is necessary to investigate the function D G \u003d F (R) to the extremum, after which we get

The value D M \u003d M 1 - M 2 is called chemical satiety and is the driving force of the dissociation process.

In fig. 3.6 shows the condition of the occurrence and growth of the embryo of the new phase.

From the analysis of dependencies, it follows that, with other things being equal, the more overheating, the smaller the critical germ and easier (faster) there is a compounds dissociation process.

Fig. 3.6. GROWTH GROWTH NEW PHASES

Thus, the growth of the nucleus of the new medium depends on the temperature, time and mobility of the particles forming a new environment. The study of the mechanism of a particular transformation allows you to determine analytical dependencies, but they are acceptable, as a rule, only for the analyzed case. At the same time, it is necessary to take into account the natural difficulty of growth associated with the "overlapping" of the embryo of the new phase and the limitation of the process of any elementary stage.

Real systems may differ significantly from the created dissociation models, when creating which should be paid to the following features: at the initial moment of time, a slower growth of the embryos are possible; The surface rate of promotion of the border of the phase partition may differ from the penetration rate into the volume; The reactivity of the boundary varies in time; The volume of products and reagents may not coincide; With reversible reactions, adsorption of volatile reaction products is possible; Perhaps the manifestation of diffusion braking; kinetic characteristics, as a rule, depend on the size of the particles; Possible difficulties in transmitting heat through the reaction products.

Some of the listed features of dissociation processes may be limiting links to which include:

1) the speed of chemical transformation (the so-called kinetic mode);

2) the diffusion rate of the gas through the coating layer (diffusion mode);

3) mixed mode (comparability of chemical transformation and diffusion rates);

4) The rate of heat transfer of the reaction through the coating layer.

Each of these stages can be expressed analytically in relation to the dissociation process of one or another compound, taking into account its features.

3.4. Oxidation of solid metals

When placing me into the atmosphere comprising O2 or other oxidative gases (CO2, H2O), its surface is covered by oxides, okalinawhose thickness increases with time. At high temperatures, this process is high temperature corrosion - develops quite quickly and leads to the loss of it when it is heated before rolling, forging.

In total, 18 ... 20 million tons are lost due to oxidation. Oxidation of me - the process is spontaneous, but it depends on a number of factors.

The oxidation process consists of the following stages:

1) the outer diffusion of oxidative gas to the surface of the oxide;

2) internal diffusion in the scale layer;

3) Chemical Act (reaction) at the borders of the phase section.

Okalina (MoO) thickness y is between two media - between me and gas; Under its limits, the concentration of O2 falls from the border of the gas / meople section to the Meo / Me / Me boundary, and the content of the IU decreases in the opposite direction. Due to this, diffusion of substances in the oxide layer is possible, which is represented in Fig. 3.7.

Fig. 3.7. Metal oxidation scheme

The diffusion coefficient in solid scale depends on its crystalline structure determined by the ratio of oxide molar fractions (VMEO) and IM (VME).

With VME\u003e VMEO forms porous The oxide layer, the oxidative gas easily penetrates into it. The following properties have the following


Menon.		Na2O.

If VME< VMeO, то оксид покрывает Ме сплошным плотным покровом, который создает значительное диффузионное сопротивление и окисление затрудняется. К данной группе относятся следующие Ме:


Menon.	Al2O3.	Cu2o.	CR2O3	Fe2O3.

Under the conditions of real oxidation of the metal, the outer diffusion of gas proceeds relatively quickly, therefore the process of oxidation of any metal can be represented as two stages:

1) diffusion O2 (other oxidizing agent) through oxide film;

2) directly act of chemical interaction on the border of the phase partition.

We derive the equation of the dependence of the thickness of the oxide of oxide from the oxidation time t at T \u003d const.

The observed speed of the process

VNB \u003d DY / DT.

The speed of the internal diffusion is defined as

where "-" is a gradient of concentrations;

SPOV, sob - the concentration of the oxidant on the reaction surface and in the volume of gas;

The speed of the chemical reaction is defined as

for n \u003d 1, https://pandia.ru/text/79/398/images/image057_8.gif "width \u003d" 115 height \u003d 52 "height \u003d" 52 "\u003e

With the steady mode of the speed of serial links to and the total speed are equal to each other:

at the same time, spots substitute the diffusion equation:

y \u003d F (T) is a differential equation.

We transfer and divide the variables:

Starting conditions: T \u003d 0, Y \u003d 0.

The desired dependence of the thickness of the oxidized diffusion layer on time:

(*)

This function is parabolic.

At t \u003d 0 and y ® 0, y2<< y, поэтому величиной y2/2 пренебрегаем:

y \u003d kx c about × t. (3.6)

This dependence is linear.

This implies:

1) the thickness of the scale layer ~ t, i.e. oxidation comes at a constant speed;

2) the oxidation rate is determined by the characteristics of the QC values, i.e. the reaction is in the kinetic region.

This refers to the metals of the I-th group.

For metals of the second group D< R; при этом t – велико. В этом случае слагаемым пренебрегаем и получаем:

. (3.7)

1) the thickness of the scale layer is proportional, i.e. the oxidation rate is reduced over time;

2) The process proceeds in the diffusion region.

Graphically, it is shown in Fig. 3.8.

Thus, with a dense scale, the oxidation reaction is first located in kinetic region And the oxide layer increases on linear dependence (in Fig. 3.8 - zone 1).

With a significant thickness of the layer, the dependence becomes parabolic and the process is limited. internal diffusion (zone 2). Between these extreme cases lies the transition zone - 3, where y and t are bound by a differential equation (*), which takes into account the peculiarities of the chemical transformation and diffusion.

Fig. 3.8. The dependence of the thickness of the scale from the time of process: 1 - kinetic region;

2 - diffusion region; 3 - transition zone

4. Metal recovery processes

4.1. Thermodynamic characteristics of recovery processes

The preparation of pure metals due to the dissociation of their oxides is thermodynamically unlikely due to the very low values \u200b\u200bof the resistance of the dissociation of compounds.

The most appropriate is the process of obtaining metals from their oxides by recovery. Such a process is essentially redox (oxidized metal is restored, and the reducing agent is oxidized) and may be generally described by the reaction

Meo + B \u003d Me + C, D G T (4.1), (4.1)

where as a reducing agent can be used both solid and gaseous substance (element).

Reaction (4.1) is essentially the sum of the formation reactions

B \u003d \u003d C, D G T (4.2); (4.2)

Me \u003d \u003d Meo, D G T (4.3), (4.3)

which are exothermic.

Spontaneous reaction flow (4.1) is possible if D G T (4.2)< D G Т(4.3).

4.2. Restoration of iron oxides solid and gaseous

restores

The universal reducing agent of iron oxides is solid carbon; When restoring gaseous, CO and H2 are often used.

The thermodynamics of the processes of reduction of iron oxides with solid and gaseous reducing agents in principle is the same.

When using carbon monoxide CO should consider equilibrium in the FEMON - CO 2 system, which are described by the following reactions:

(4.4)

EN-US "\u003e EN-US"\u003e POSITION: Absolute; z-index: 5; left: 0px; margin-left: 234px; margin-top: 12px; width: 11px; Height: 88px "\u003e (4.8)

Fig. 4.1. Equilibrium composition of the gas phase systemFEMON - CO - CO 2

The diagram does not have a zone of the stable existence of the phase FE 2O 3, since, according to calculations, this phase is in the temperature interval with an unstable already under the content of CO\u003e 0.01%.

The point O is an irrevalted equilibrium point with a gas phase of three solid phases.

When used as a reducing agent of hydrogen or some other reducing agent, the equilibrium composition curves will be calculated in the same way.

When used as a redundant carbon iron oxides, the process can be described by reactions that meet the equilibrium in the system.
Fe 2O 3 - Fe 3O 4 - FEO - Fe - C - CO - CO 2 containing seven components.

However, taking into account the instability Fe 2O 3, it is advisable to analyze the following chemical equilibriums:

Fe3O4 + CO \u003d 3FEO + CO2;

FEO + CO \u003d Fe + CO2;

2CO \u003d C + CO2.

In addition to private equilibrium, in accordance with the rules of the phases, simultaneous equilibrium of five phases is possible - four solid and gaseous (mixtures of CO and CO2).

The equilibrium curves of these reactions are shown in Fig. 4.2.

font-Size: 13.0PT "\u003e Fig. 4.1. Equilibrium monoxide content

carbon with indirect reduction oxides

iron and solid carbon gasification reaction

The quantitative characteristics of the equilibrium in the system under consideration can be obtained by deciding together the equations expressing the dependence of the constants from the composition of the gas phase. From the solution of the system of these equations, it follows that with an increase in pressure in the temperature of the oxide for the beginning of the reduction of iron oxides, and with a decrease in pressure, on the contrary.

Thus, phase equilibriums in the FE -O system in the presence of solid carbon are determined by the temperature and total pressure of the gas phase
(CO + CO2).

4.3. Mechanism and kinetics of recovery processes

The mechanisms for restoring metal oxides with gases and solid reducing agents are excellent and have their own characteristics.

When restoring the gases, this process proceeds at least three stages:

1) adsorption of recovery on the reaction surface;

2) the transition of oxygen from the oxide grille and its compounds with the adsorbing reducing agent molecules with the simultaneous formation of the new solid phase.

3) desorption of gaseous recovery products.

This theory received the name of the adsorption-autocatalytic, and the mechanism itself can be submitted by the scheme:

Meo (TV) + B (gas) \u003d \u200b\u200bMeo (TV) × in (ADS),

Meo (TV) × in (ads) \u003d me (TV) × in (ADS),

Me (TV) × in (ads) \u003d me (TV) × (gas)

Meo (TV) + B (GAZ) \u003d IU (TV) × (gas).

There is also a two-way diagram consisting of an oxide dissociation stage with the formation of molecular oxygen and a stage of a compound with a reducing agent in the gas phase.

According to adsorption-autocatalytic theory, the recovery process is autocatalytic - the formation of a solid product of the reaction accelerates the process of its formation. At the same time, the adsorption of the gas-reducing agent molecules is developing in different ways, depending on the structure, structure. At a certain stage of recovery, a maximum characteristic of autocatalysis is observed, which corresponds to the kinetic recovery regime.

In general, the kinetic process of restoration of metal oxides gases is heterogeneous, consisting of the following stages:

1) the external diffusion of the reducing agent from the gas stream to the surface of the reduced oxide;

2) the internal diffusion of the reducing agent to the reaction proportion through the pores and defects of the lattice layer of the solid product of the reducing agent;

3) chemical reaction with subsequent crystalochemical transformation of metal oxide into lower, up to metal;

4) The removal of gaseous recovery products into the gas flow due to internal and external diffusion.

Any of these stages can be in principle a limiting, that is, to determine the speed of the recovery process. Depending on the diffusion rate and chemical transformation, a stepwise or zonal recovery is possible, which corresponds to the principle of the sequence.

The step type of process is observed at kinetic mode, zonal - with diffusion. With comparable diffusion rates and chemical reactions, the recovery process will flow in a blended, or diffusion-kinetic mode, which is the most difficult.

Different factors are influenced by the reduction rate of gases, the following are the following: sizes of pieces of oxide material, porosity of ore, speed of the gas-reducing gas stream, composition of gas, pressure and temperature.

Reactions of direct reduction of metal oxides are more complex compared to the reduction of gases.

Restoration of oxides of solid carbon can be assessed by reaction

Meo (TV) + C (TV) \u003d Me (TV) + CO2.

However, this equation does not reflect the actual mechanism of the process flowing into several steps with participation, as intermediate products, gases.

There are several coaltermic solution of oxide recovery schemes.

The two-step scheme is designed and represented by equations

Meo + CO \u003d ME + CO2

C + Sog \u003d 2

Meo + C \u003d Me + CO.

According to the diagram, the interaction of metal oxide with solid carbon is reduced to the reduction of gas gas. This allows you to apply an ad-catalytic theory to explain the processes of direct reduction, and the role of solid carbon is reduced to the reaction of CO for the gasification reaction. Kinetically, according to this scheme, it is possible to restore those metals that are easily restored by gases (Fe, Ni, Cu, etc.). The lower temperature limit of the interaction according to this scheme is associated with a low rate of carbon gasification reaction under reduced temperatures, and this stage is often limiting. Therefore, decisive for the process of direct reduction of metal oxides are the factors affecting the rate of gasification reaction - the temperature, carbon activity, the presence of catalysts.

There is a dissociative scheme according to which the process of oxide dissociation is possible with the subsequent interaction of oxygen with carbon according to the scheme

Me \u003d ME + 1 / 2O2

C + 1/2 \u003d with

Meo + C \u003d Me + CO.

Such a scheme is acceptable for oxides with high dissociation elasticity (Mn O2, PB O2, CU O, CO 3O4).

Oxide - the sublimation scheme was developed, according to this hypothesis, the reduction of a number of oxides can pass through the sublimation of the oxide with subsequent condensation (adsorption) of its vapors on the carbon surface:

Meo (TV) \u003d Meo (Gas)

Meo (gas) + C (TV) \u003d Meo (ADS) · C (TV)

Meo (ADS) · C (TV) \u003d Me (TV) · Co (ADS)

Me (TV) · Co (ADS) \u003d Me (TV) + CO (gas)

Meo (TV) + C (TV) \u003d Me (TV) + CO (gas).

This scheme is characteristic of both volatile oxides (MO O3, W O3, CR 2O3) and explains their recovery at 630 ... 870K, when the interaction according to other schemes due to the low velocities of the carbon gasification reaction and the thermal dissociation of oxide is impossible, as well as for durable oxides (Al 2O3, Mg O, Zn O2), the sublimation of which is accompanied by the formation of the vapor of oxide and lower gaseous oxides (Al 2o, Si o).

According to the recovery contact scheme, the interaction occurs at the point of contact of solid phases - oxide and carbon. After direct contact, a separating interlayer of the product is formed, and the restoration comes with the diffusion of reagents through this layer.

A number of carbothermal recovery patterns is explained within the framework of the gas framework: the effect of CO's speed, the presence of carbon in condensation products in zones removed from the reactive mixture, the effect of swelling of ore-coal pellets, autocatalysis.

Thus, different oxides can interact with carbon in various schemes, and others can be implemented simultaneously with the main mechanism. The proportion of each mechanism in the process of recovery varies depending on the conditions - temperature, pressure, the degree of mixing of reagents and the degree of recovery, other factors.

5 . Metallurgical melts

5.1. general characteristics

High-temperature metallurgical processes proceed with the participation of liquid phases: metal, oxide (slag), sulphide (matte), salt. The interaction between liquid phases and with the obligatory participation of gas depends on the structure (structure) and the properties of metallurgical melts.

With regard to the nature and structure, all fluids are classified as follows:

1) with hydrogen bonds (water, alcohols, organic acids);

2) with molecular bonds (benzene, paraffin);

3) with ionic bonds (oxide and sulfide melts, aqueous and other solutions of salts, alkali, acids);

4) with metal connections (the interaction of cations with free electrons).

The oxide and sulfide melts participating in metallurgical processes are multicomponent fluids and have a complex structure. In melts of salts belonging to ionic liquids, there is a strong interstitial interaction and a high concentration of particles in a unit of volume. Industrial metal melts are multicomponent fluids containing metal and metalloid components.

When obtaining a metal melt of a given composition, seek to reduce the loss of alloying elements with a slag and a gas phase. This is facilitated by knowledge of the regularities of the redistribution of elements between contacting phases, the ability to calculate the thermodynamic activity of components in metallurgical melts.

To solve such tasks, it is necessary to know the structure (structure) of the melts and the nature of the forces acting between the structural units of the melt. To estimate the speed of the processes flowing in the system, it is necessary to know a number of physicochemical properties of melts.

Under the structure or structure of the melt, the quantitative description of the mutual location in the space of the components of their particles is understood. The structure of the melt is interrelated from the electoral nature of the particles, the magnitude of the interaction forces between particles and with its physicochemical properties, which are often called structurally sensitive properties.

5.2. Metal melts

Clean liquid metals usually belong to the so-called simple liquids, which are liquefied inert gases with Vandervalian interaction forces. In liquid metals, the inter partition is carried out by collectivized electrons; The presence of electrical conductivity, thermal conductivity, as well as viscosity and adsorption along with other metals properties are explained.

At temperatures close to the crystallization temperature, the structure of liquid metals is close to the structure of solid crystalline bodies. This similarity consists in comparability of the nature of inter-partic interaction and thermodynamic properties. In a liquid state, atoms (ions) are at close distances, but do not form a strictly periodic regular structure, that is, far order characteristic of solid crystalline bodies.

Introduction to the metal of various impurity elements (including alloying) changes the electronic structure of the melts, and, depending on the nature of the impurity, the shape of its existence in the melt differs from the form of the existence of the solvent.

Thus, such elements such as manganese, chromium, nickel, other metals, little different from iron by electronic structure, have unlimited solubility in liquid gland and high - in solid. They form solid substitution solutions with iron, while occupying part of the nodes in the crystal lattice.

Elements such as carbon, nitrogen and hydrogen are forming solutions of the introduction, while located in the interstices of the crystal iron grille.

Silicon and phosphorus in liquid gland dissolve unlimitedly, and in solid - their solubility is limited. In iron melts, they form separate groups of iron atoms with silicon and phosphorus, with a predominance of a covalent bond.

The impurities dissolved in liquid gland (or a different solvent) change the properties of metal melts and affect the nature of steel-smelting processes. Such properties include viscosity, surface properties, density, electrical conductivity and thermal conductivity.

5.3. Thermodynamic properties of metal melts.

Parameters of interaction

For metal melts, which are inherently solutions, characterized by complex physico-chemical interaction between particles from which they consist. The reliability of the thermodynamic description of metallurgical systems is determined by the degree of development of one or another thermodynamic theory. At the same time, depending on the nature of these or other assumptions, statistical theories are divided into strict theories (for example, quantum-mechanical); built on the numerical experiment of theory; Model theories.

The latter received quite widespread - this is the theory of perfect solutions, the theory of ideal dilute solutions, the theory of regular solutions and others. One of the reasons for the administration of such theories is the absence of a common thermodynamic model of solutions.

When describing the thermodynamic properties of metal melts from the models used, the method of interaction parameters is most often used.

This method is used to take into account the influence of all components of the solution on the activity of the component under consideration (for example, a component A is a solvent, components B, C and D - added impurities). The interaction parameters are determined as a result of decomposition in a series of Taylor redundant energy For a component in near the point corresponding to a clean solvent:

https://pandia.ru/text/79/398/images/image083_4.gif "width \u003d" 39 "height \u003d" 25 "\u003e on the molar fractions of impurity elements are called molar parameters of the interaction of the first order, the second - second order HTTPS: / /pandia.ru/text/79/398/images/image086_4.gif "width \u003d" 28 "height \u003d" 28 "\u003e.

Taking into account this expression (5.1) for solutions with low values \u200b\u200bof dissolved components (B, C, D, ...) can be written as

Or for i-component

. (5.2)

For multicomponent solutions, 1% diluted solution is usually taken for the standard state of the substance. In this case, instead of (5.2) record

or in general (5.3)

here

5.4. Slag melts. Composition, structure, thermodynamic properties

The metallurgical slag is a multicomponent (mainly oxide) solution that interacts with the metal melt and the gas phase of the metallurgical unit. The slag may include sulphides, fluorides, other non-metallic inclusions. In the course of melting metal, the slag performs essential technological functions (for example, such as metal protection against the atmosphere of the unit; absorption of harmful impurities from metal; participation in oxidative processes; metal diffusion deck).

The structure of the slag melt is determined by the nature of structural units and their distribution in space. Comprehensive study of the basic physicochemical properties of slag melts - viscosity, diffusion, adsorption, carried out, including with the help of X-ray diffraction studies of solid and liquid slags, showed that slag melt consists of ions - cations and anions.

The composition of slags significantly affects their main properties, among which the basicity should be selected - the ratio of the concentration of oxides with pronounced basic properties, and oxides with acidic properties. Further, depending on the composition of the slags are divided into basic (they prevail the main oxides - CaO, MGO, MNO, etc.) and acidic (SiO 2, Al 2O 3, TiO 2).

The composition of the slag and its structure affects the physico-chemical properties: density, surface properties, viscosity, diffusion.

Density and willed volume are structurally sensitive properties, these characteristics are used to calculate the kinetic properties of ionic melts. The effect of the composition is determined by the change in the coordination number and is characterized by a change in free volume. Temperature dependence is associated with a change in the interatomic distance due to an increase in the amplitude of the fluctuations of atoms.

When analyzing surface properties, it is established that for most double systems, the surface tension varies linearly with a change in the composition.

Another major characteristic of slag melts is viscosity varies in the range of 0.1 ... 1.0 Pa · C (due to the presence of large structural units of the type of silician complexes), which is higher compared to metal melts.

The dynamic viscosity η and the kinematic ν are associated with the relation η \u003d 1 / ν.

The dependence of viscosity on temperature is expressed by the equation

η \u003d AECR (Eη / RT)

where Eη is the activation energy of viscosity.

The thermodynamic properties of slag melts are described using various theories - molecular and ionic, which are based on the results of studies of the mineralogical composition of the crystallized slag and the synthesis of experimental data.

A variant of the molecular theory of the structure of liquid slag, developed by G. Schenki, is simplicity and is based on the approval that the molecules of free oxides are considered as a single slag structures (SIO, SiO 2, Feo ...) and their connections.

From the manifold of oxide compounds, 5: 2Feo · SiO 2, 3SAO · Fe 3O 4, 2mnO · SiO 2, CaOs · SiO 2, 4 SAO · P2O5 are selected. These compounds satisfactorily describe a wide range of slag properties, including the distribution of elements between the metal and a slag based on the equilibrium equilibrium reactions of the diagnosed compounds.

However, the main feature and lack of molecular theory of slag melts is the lack of accounting for the real structure of slag melts. However, the accumulated material allows you to evaluate some thermodynamic characteristics - for example, the activity of AI components.

The theory of perfect ion solutions (author) is based on approval that the slag solution completely dissociates on ions (cations and anions); The ions of one sign are energetically equal; The nearest neighbors of each ion are the opposite sign ions; The solution is formed without changing the volume; With thermal motion, permutations are possible between the ions of one sign. The activity of the components of such a melt is calculated as a product of ionic fractions of cations and anions.

For example, the activity of calcium sulfide CAS will be determined by the ratio

where HSA, XS - ion shares of calcium cation and sulfur anions, respectively.

The theory of perfect ion solutions can be used to determine the activity of components in highly basic slags, however, an increase in the share of SiO 2 and Al 2O 3 to 20% gives a strong discrepancy between theory and experience, therefore, in practical calculations, this theory is not used.

However, the main static provisions of this model are applicable in the theory of regular ion solutions developed and tested.

The peculiarities of this theory include the following provisions: the entropy of the solution is not considered ideal and is calculated on the theory of perfect ion solutions; The solution consists of the simplest atomic ions (cations - ion ions Ca2 +, Fe 2+, Al 3+, and anions - metaloid ions O2-, F -, S 2-); The nearest neighbors of ions are the ions of the opposite sign; The solution is formed without changing the volume, with the release or absorption of heat.

In calculating the chemical potentials of the components of the solution - as in determining the activity of components; In this theory, it is necessary to take into account the mixing energy of the components Qij, which is based on the results of experimental studies of solutions from compounds containing cations I and J. For this theory, it is characteristic that the relationship between the composition and thermodynamic functions is set more strictly and reasonably, therefore the accuracy and reliability of the calculations are higher.

In the polymerization theory of slag melts, it is assumed that the forming solutions of ions are energetically unequal, the polymerized complexes are formed, in which the binding energy of complexes with other structural units of the solution.

According to the theory of solutions as phases with a collective electron system (the main provisions are designed), not chemical compounds, but the elements of the periodic system, are not selected as the component of the slag solution, and the composition of the solution is expressed in atomic fractions. At the same time, the electrons of all solution atoms form a single quantum-mechanical system. The activity of the compound AM BN in slag solution is defined as

where https://pandia.ru/text/79/398/images/image095_3.gif "width \u003d" 23 "height \u003d" 25 src \u003d "\u003e - the activity of elements A and V.

The activity of the grade I element is determined by the atomic fraction of this component and the energy of the interaction with the component J. At the same time, the energy of the interaction of EIJ is defined as

Eij \u003d 1/2 (χ1 / 2 - χ1 / 2) 2,

where χi and χj are the atomic parameters of atoms I and J, determined from the values \u200b\u200bof the standard enthalpies of the formation of various compounds.

6. Gaza in steels. Nitrido formation processes

For high-temperature metallurgical processes, the interaction of a metal melt with slag and gas phases is characterized. The completeness and speed of interaction of gases primarily with liquid metals determines the quality of metal products.

The dissolution of ductoman gases (oxygen, hydrogen and nitrogen) in the liquid metal of the same type, obeys the law A. Syverts (known as the law of a square root) and occurs by the reaction

Reaction equilibrium constant (6.1) has the form

, (6.2) where

The equilibrium concentration of gas [g] in metal at \u003d 1 atm is called solubility and is numerically equal to the reaction equilibrium constant (6.1) for the metal-gas two-component system.

At a temperature of 1600 ° C, the limiting solubility of oxygen in the liquid gland is 0.22%, for nitrogen - 0.044%, for hydrogen - 0.0026%.

The processes of dissolving gases in most metals (iron, nickel, etc.) are endothermic, therefore, with increasing temperature, the solubility of gases increases. The exception is the solubility of nitrogen in -fe, which decreases with an increase in temperature at the points of the phase transitions of iron from one modification to another (-fe -fe, -fe https://pandia.ru/text/79/398/images/image102_2.gif "width \u003d" 13 "height \u003d" 20 src \u003d "\u003e - Fe) and when melting (-fe en-us"\u003e Fe -zh) the equilibrium concentrations of gases in the solution change jumps like.

According to (6.2), the solubility of gases has influence and pressure. With an increase in pressure, the reaction equilibrium (6.1) is shifted towards a smaller number of gas moles, i.e. right. The feasibility of the Law of Syverts indicates the ideality of the resulting solution. In the presence of other components dissolved in the metal, the equilibrium concentrations of gases become different. This influence can be taken into account using the parameters of the interaction of the component with a dissolved gas.

In the case when<0, происходит снижение коэффициента активности газа в расплаве и повышение его растворимости. Например, элементами, повышающими растворимость водорода в железе, являются титан, ниобий, ванадий. Снижению растворимости водорода в железе способствуют такие элементы, как углерод, алюминий , кремний (для них >0).

Almost in the same sequence affect the specified components on the coefficient of nitrogen activity and its solubility.

A strong decrease in the solubility of hydrogen and nitrogen in crystallization of iron and its alloys is accompanied by a number of undesirable phenomena. Hydrogen in molecular form is isolated in defective places (micropusters) of the crystallized metal. With a decrease in the dimensions of these microdefects, during subsequent plastic processing, it creates high pressure, as a result of which voltages arise in the metal leading to a decrease in plasticity, as well as a breakdown of continuity.

The effect of alloying elements on the solubility of nitrogen in iron-based melts or nickel can be estimated using experimentally installed.

In the interaction of nitrogen with melt, doped nitrido-forming elements, the formation of a solution of Fe-R-N, equilibrium with a gas phase, and with an increase in the content of R increases the solubility of nitrogen.

With certain contents of the R component R from the melt, a refractory compound - RN nitride may be isolated. Elements IVA subgroups Ti, Zr, HF are the greatest affinity for nitrogen, which are mainly used for binding nitrogen in liquid metal.

Dispersed carbides that are distinguished from the solution cause a strong decrease in the plasticity of the metal and increase its hardness.

The features of the interaction of nitrogen with metal melts reflect the diagram of the state of the ME-R-N, the fragment of the isothermal section of which in areas rich in the metal is shown in Fig. 6.1.

Lines that limit the stability areas of the phases are described by the corresponding equilibrium thermodynamics equations.

As can be seen from the diagram, with small quantities of the nitride-forming element, there is a two-phase region of stability of the liquid phase with gaseous nitrogen. The coordinates of the lines of the AB separating this area (I) and the area of \u200b\u200bfluid stability (II) can be determined by analyzing the equation:

Under ATM, nitrogen activity is equal to the reaction equilibrium constant (1). Nitrogen concentration at point A is equal to its solubility in the binary system ME-N.

Fig.6.1. Isothermal scheme of the state diagram of the ME-R-N system

In fig. 6.1 The following phase stability areas are shown:

I - w + n2,

II - F

III - w + Rn,

IV - F + RN + N 2.

The intersection of nitride formation (BD) and lines (AB) corresponding to the solubility of nitrogen in the FE-RN melt at font-formily: symbol "\u003e - [R] of the concentration triangle at a point corresponding to the connection RN, and the line B is at a point corresponding to the clean Nitrogen at atm.

7. Decking of metal melts

In the process of the oxidative period, the smelting of steel in the steel-smelting unit entering the metal oxygen (from the oxidative slag, pondered into a metal bath tube) is consumed mainly on the oxidation of impurities (C, S, P, SI) and some alloying components, but part of it remains in the metallic melt.

The solubility of oxygen in the gland under the pure iron slag is estimated on the basis of reaction

(FEO) \u003d +. (7.1)

Chipman found that for reaction (7..gif "width \u003d" 176 Height \u003d 47 "Height \u003d" 47 "\u003e.

At T \u003d 1600 ° C (1873K), the limiting solubility of oxygen in the gland is 0.21%.

However, in real conditions, steel smelting slags besides FeO, contain numerous oxides and other inclusions, therefore. Therefore, the oxygen content in liquid steel does not reach the solubility limit and is at the level of 0.06 ... 0.08. At the same time, with a content in a metal melt, more than 0.05 ... 0.06% with the oxygen content in the metal is determined by the development of carbon oxidation reaction

+ \u003d (CO). (7.2)

Upon reaching the metal melt of the equilibrium state at T \u003d 1873, the ratio should be performed · \u003d 0.0025, but in real conditions of smelting steel in industrial aggregates carbon oxidation reaction does not reach equilibrium - in particular, due to the conditions of formation of bubbles of CO. In this regard, in the course of smelting steel under the oxidative slag, the oxygen content in the metal is higher than the equilibrium and approaches it with a carbon content of less than 0.15%. In fig. 7.1 shows the dependence of the oxygen content in the metal melt from the carbon content.

Fig. 7.1 Changing the oxygen content in iron-carbon melt: 1 - equilibrium curve; 2 - region of actual concentrations of smelting steel

The actual concentrations of oxygen in steel for all types of processes are laid in one area. This indicates that when\u003e 0.05 ... 0.06 carbon oxidation reaction has a decisive effect on the oxygen content in steel. For< 0,05…0,06 содержание кислорода в металле соответствует равновесному с углеродом и бывает ниже его. Следовательно, равновесное со шлаком содержание кислорода в Me достигает величин, соответствующих равновесию с углеродом или даже меньше их.

The reaction (7.2) is exothermic, so when cooled and crystallizing the metal melt, the value · at p \u003d const decreases; Excessive oxygen concentrations are even greater, which leads to the formation of gas bubbles that reduce the density of the ingot, and isolating the inclusions of iron oxides and its solutions with sulfides along the grains of crystallizing metal grains. These oxysulfides give metal blades due to low melting temperatures.

The liquidation of elements, especially oxygen, also have a strong effect: in the process of crystallization, its content in the initial solution in the edge of growing crystals is significantly higher than the average in the volume of liquid metal, which causes intensive carbon oxidation.

In this regard, one of the main tasks of the final smelting period is the removal of excess oxygen from the liquid stage, which is achieved by the deoxidation of the metal melt.

Under deoxidation, a complex of operations to reduce the oxygen content in liquid steel is understood.

The main tasks of the deoxidation are:

- reduction of oxygen content in liquid iron by additives of elements with a large affinity to oxygen than in iron, to a level that ensures the production of dense metal;

- Creating conditions for more complete removal of deoxidation products from liquid steel.

If the first task is considered using the laws of chemical thermodynamics, the second is solved using the chemical kinetics apparatus.

The thermodynamic approach allows you to identify the connection between the oxygen content in the liquid steel and the content of the element - the deoxidizer R, determine the degree of temperature effect on the nature of this connection, as well as calculate the minimum oxygen content in the metal melt when it is decking it with R.

The most common method of deoxidation is precipitating, or the deep method according to which elements are deployed with higher affinity for oxygen (Si, Al, Ca) than iron. These elements bind oxygen into durable non-metallic inclusions (usually oxides), the solubility of which in the gland is several orders of magnitude lower than the solubility of FEO. These inclusions are isolated in a separate phase as a small suspension, which having a smaller density compared to steel, partially pops up into the slag, and partially remains in the crystallized metal in the form of non-metallic inclusions, worsening its quality.

The precipitating (deep) deoxidation can be described by the type reaction

. (7.3)

Subject to the equilibrium constant of this reaction takes the form

(7.4)

where AI is the activity of the i-th component in the melt.

To calculate the activity of the melt components, 1% diluted solution is usually taken for the standard condition.

Diffusion deoxidation is achieved when establishing equilibrium by reaction

(FEO) \u003d + [O]

The method is based on the idea of \u200b\u200bthe desire for the equilibrium distribution of the substance between the uninhabited liquid phases - ME and slags. At the same time, the ratio is performed

(7.5)

When decreasing the activity of iron oxides in a slag oxygen diffuses in the metal to the boundary of the phase separation and in the form of steam ions Fe 2+ and O 2- goes into the slag.

The advantage of the method is the absence of any reaction products in the metal after the removal of oxygen.

This method is implemented in a chipboard with a small amount of slag and low oxygen content in the gas phase. In other steel-smelting units, diffusion deoxidation today is not used due to the low speeds of the process.

Most often, the diffusion deoxidation is used as a concomitant process when processing liquid steel in the bucket of synthetic lime-aluminous slags with a low FEO (less than 1%). When crushing the metal on fine drops, the metal-slag contact surface increases thousands of times, the presence of convective currents accelerates the process of not only deoxidation, but also desulfurization of steel.

Another deoxidation method is a vacuum deoxidation, which is based on the decarburization reaction from (7.2).

Reducing the pressure displays the equilibrium of this reaction in the forward direction. The advantage of this method is the absence of deoxidation products. This method is implemented under the extra-refined steel processing.

There is a comprehensive deoxidation based on the use of complex deoxidizers - alloys of two or more components (silicocallations, silicomargana and others). The advantages of using such deoxidizers are predetermined by a significant improvement in the thermodynamic conditions of deoxidation and more favorable kinetic conditions for nucleation, consolidation and removal of non-metallic inclusions.

Thus, the addition of Mn in Fe with a deoxidation of its silicon leads to an increase in the deoxidative ability of the latter.

The effect of increasing the deoxidant ability under the influence of the second component is explained by a decrease in the thermodynamic activity of the formed oxide in the complex products of deoxidation, which differ significantly from products with separate deoxidation.

Under the deoxidative ability of the element, the equilibrium concentration of oxygen dissolved in the gland (metal) corresponding to the temperature of this element is understood at this temperature. Obviously, the smaller this concentration with a given deoxidizer content, the higher the deoxidant ability of the element.

M / N LG [R] - M / N LG FR - LG FO. (7.9)

Equating the right-hand part of equation (7.10) to zero and solving it relative to R, we find the concentration of the deoxidizer R corresponding to the minimum content of oxygen in the metal; At the same time, the values \u200b\u200bof the coefficients of the components are found in relations (7.7) and (7.8):

(7.11)

(7.12)

Substituting the value [R] from the relation (7.12) to equation (7.9), we determine the minimum oxygen concentration in the metal melt, a deoxidizing element R:

(7.13)

In fig. 7.2 shows the deoxidant abilities of some elements in liquid gland at T \u003d 1600 ° C.

The oxygen content is complex dependent on. For small concentrations of the deoxidizer with an increase in R, the oxygen content drops. Further increase leads to an increase in oxygen concentration in metal. However, with an increase in oxygen content caused by a decrease in activity coefficient, the activity of oxygen is reduced, which is confirmed by experimental data. Fractures on curves of the dependences of oxygen content in liquid gland in Fig. 7.1 are a consequence of the formation of different deoxidation products when changing the deoxidizer content.

The birth of the deoxidation products can be carried out in a homogeneous phase (the so-called spontaneous nucleation) or on finished surfaces (the surface of the walls of the unit, slag, weighted inclusions, oxide films on the deoxidizers).

In all cases, the emergence of new phases is carried out as a result of fluctuations - random accumulation of particles (atom, ions) differing in the composition of the average content in the metal. These fluctuations, depending on their magnitude and external conditions, may disappear or, overcoming some energy barrier, develop, interpretable in inclusion.

Fig. 7.2 Deadsectivity of elements in liquid gland at T \u003d 1600 ° C

It was experimentally confirmed that in the homogeneous system, in the formation of the embryos of the new phase, they initially transfers those having increased affinity to oxygen and causing the largest surface tension on the border of the Metal-germ section of the new phase. With the subsequent inclusion growth, the concentration of active ingredients involved in the process of forming a new phase is reduced. Those components of the melt, which contribute to the reduction of the thermodynamic activity of oxides, isolated in fluctuations, facilitate the formation of embryos, and contributing to the decrease in the activity of the deoxidizer and oxygen in the metal make their separation difficult.

In the case of the origin of inclusions on gas surfaces, it is essential, in addition to the above-mentioned homogeneous phases, is the effect of wetting the surface of a separable phase. The less wetting angle, the smallest fluctuations become embryos. The formation of the embryos is facilitated by prefabricated substances, capillary-active on the border of the phase partition.

In the event of a significant deviation from the equilibrium state, homogeneous embryo formation is determining. When reducing the oversaturation of one or another component, the role of finished surfaces as nucleation centers increases. The effect of finished surfaces, especially when allocating solid inclusions, especially efficiently, the closer the orientational and dimensional correspondence of the crystals of a separate inclusion and the existing substrate.

The originating inclusions (their initial size of order 1 nm) are enlarged as a result of coagulation (compound) of particles in a collision and separation of substances from the metal melt on these particles due to the oversaturation of the solution. The rate of coagulation affects the frequency and effectiveness of the collision of particles, which is due to the Brownian movement, as well as due to the difference in movement speeds, which is caused by the unequal dimensions and densities of the particles and the presence of convective currents

Convective currents ensure the delivery of deoxidation products from the depth of metal to the surface of the Metal-slag section. The movement of the inclusion in the metal boundary with a slag is determined by the direction and the value of the resultant number of forces: ejecting (archimedes) f a, due to the difference in metal densities and slag and directed vertically up; capillary fap caused by a gradient of the concentration of capillary and active substances and aimed in the direction of their higher concentration; inertial - centrifugal F C, caused by the curvature of the trajectory and directional in the depths of the metal, since the inclusion density is less than the density of steel, and the inertia f and the direction of which depends on the direction of the particle movement: for free pop-up inclusions, it is directed vertically upwards, and for portable streams - coincides with the direction of flow.

Depending on the size and shape of the inclusions, metal deoxidices and slag, the hydrodynamics of streams, the effect of each of the specified forces on the speed of the particle approach to the surface of the slag is different. Large inclusions are suitable for the border predominantly under the action of the pushing force, smaller - under the action of capillary, especially with a large gradient of oxygen concentration.

With a decrease in the surface on which these forces apply, pressure increases and a breakthrough of the metal layer is realized faster. It is easier to overcome such resistance to solid inclusions of irregular shape with sharp grains, more complicated - with flat.

Thus, the more complete steel is deoxidized and the inclusion is removed from it, the higher the quality of the finished metal.

8. Distribution of elements between metal and slag

The distribution of elements impurities of a liquid metal or a metal (element) between the metal and slag phases depends on the chemical affinity of the elements to oxygen, the composition of the slag, the interaction of the elements among themselves in the metal and slag, temperature.

The influence of the chemical composition of the slag is associated with the chemical properties of the oxide formed during the oxidation of the impurity element.

The effect of temperature is manifested depending on the sign of the thermal effect of the reaction of oxidation of impurities and transition of oxide into a slag, which is usually positive (ΔH< 0).

It is possible to characterize the distribution of elements due to the chemical reaction between the metal and the slag using the distribution coefficient L i.

This indicator under certain conditions may be a quantitative characteristic of the impurity distribution due to the oxidative reaction with a change in the electronic state of this impurity when moving from one phase to another.

It is possible to express the equilibrium distribution indicator from the equilibrium constant of the element oxidation reaction occurring, for example, in the interaction of contacting phases of metallic and slag melts:

X [e] + y (FEO) \u003d (EX O Y) + Y; (8.1)

. (8.2)

Taking into account (8.2) the distribution coefficient of the element [e] will be expressed as:

. (8.3)

Analysis of equation (8.3) allows you to identify the conditions for the transfer of elements from one phase to another: from metal in slag or vice versa. Below are examples of the distribution of some elements between metal and slag.

For silicon, the equilibrium of the interfacial distribution reaction will express as

2 (FEO) \u003d (SiO 2) + 2; (8.4)

. (8.5)

The conditions of the maximum transition of silicon from metal to slag melt will be the following:

1) a decrease in temperature that allows you to increase the value of KSI, since for this chemical reaction ΔH< 0;

2) an increase in activity (FEO) in slag and metal oxidation [% o];

3) decrease in the activity coefficient of particles containing Si in the slag;

4) an increase in SI activity in a metal melt.

Conditions 2 and 3 are performed with a certain slag base: an increase in% Cao reduces the activity coefficient of particles containing Si due to their groups with Ca 2+ ions.

Silicon has a high affinity for oxygen, for it EN-US "\u003e 2 [p] + 5 (FEO) + 4 (CaO) \u003d (4 (CaO) · (P 2 O 5)) + 5; (8.6)

(8.7)

The activity of particles containing phosphorus in a slag decreases with an increase in CaO content, which is associated with the formation of 4CAO · P 2O groupings 5. From analysis (8.6) and (8.7) it follows that for more complete translation of the phosphorus of metal in the slag, it is necessary to increase en -US "\u003e Feo, as well as Cao. At the same time, the greatest influence of one of these values \u200b\u200bis manifested at elevated values \u200b\u200bof another.

The conditions for the maximum transition of phosphorus from metal in the slag are:

1) an increase in FEO activity (FE 2+ and O2-) ions in a slag, which allows to obtain the oxidized form of phosphorus (P 2O 5);

2) increasing the content of CaO and the basicity of slag, which reduces the activity of particles in the oxide melt containing phosphorus;

3) Decrease in temperature: This factor should be taken into account with other things being equal, since the increase in temperature in modern oxidative processes does not reduce the possibility of removing phosphorus when obtaining more major dophosporizing slags;

4) Presence in the metal melt of elements that have positive interaction parameters with phosphorus (carbon, silicon, oxygen).

Bibliographic list

1. The theory of metallurgical processes: a training manual for universities /, et al. - M.: Metallurgy, 1989. - 392 p.

2. Popel, metallurgical processes: Tutorial for universities / ,. - M.: Metallurgy, 1986. - 463 p.

3. Caderer, and calculations of metallurgical systems and processes: a tutorial for universities / ,. - M.: Misis, 2002. - 334 p.

4. Grigoryan, Basics of Electrostalville Processes: Textbook for universities / ,. - M.: Metallurgy, 1989. - 288 p.

5. Cossacks, on the theory of metallurgical processes: a tutorial for universities. - M.: Metallurgy, 1988. - 288 p.

Introduction ............................................................... ... ............ ............ 3
1. Composition and properties of high-temperature gas atmosphere

1.1. Thermodynamics of the gas atmosphere ................................................ 3
1.2. Homogeneous gas processes ................................................... .. 7
2. Analysis of the combustion processes of solid carbon ....................................... 9
3. Evaluation of the strength of chemical compounds ....................................... .. 11
3.1. Dissociation of carbonates ....................................................................... .. 12
3.2. Dissociation of iron oxides ................................................... ... 13
3.3. Mechanism and kinetics of dissociation processes .............................. .. 15
3.4. Oxidation of solid metals ................................................... ... 18
4. Metal recovery processes

4.1. Thermodynamic characteristics of recovery processes ...... .... 21
4.2. Restoration of iron oxides solid and gaseous

restorers ................................................................................ .. 21
4.3. Mechanism and kinetics of recovery processes ........................... .. 23
5. Metallurgical melts

5.1. General characteristic ............................................................ .. 26
5.2. Metal melts. ............................................................ 27.
5.3. Thermodynamic properties of metal melts. Parameters

interaction ....................................................................... 28
5.4. Slag melts. Composition, building, thermodynamic properties ... 29
6. Gaza in steels. Nitrido formation processes ............................ ......... 31
7. Decking of metal melts ................................................ 34.
8. Distribution of elements between metal and slag .................. .. ...... 40
Bibliographic list ............................................................... 43

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n1.DOC.

FGOU VPO

Siberian University of Federal

Institute of non-ferrous metals

And materials science

Theory of metallurgical processes

Abstract lectures for students specialty

Engineer physicist

Krasnoyarsk 2008.

UDC 669.541

BBK 24.5.

Reviewer
Approved as a textbook
I.I. Kopach
By 55. The theory of metallurgical processes:Studies. Manual for the specialty "Engineer-physicist" / SFU. Krasnoyarsk, 2008. - 46 s.

ISBN 5-8150-0043-4
The manual describes the theoretical provisions of the main processes of metallurgical production, such as: dissociation, redox processes, chemical and physical methods of refining, slags of metallurgical production and sulfide metallurgy.
Siberian Federal Uniaversate, 2008

In in e d e n and e

Dissociation of chemical compounds
The composition and properties of the gas phase at high temperatures.
Oxidative and notification processes.
1. Hydrogen recovery
2. Restoration of solid carbon
3. Gas Recovery S.
4. Restoration of metals

4. Rafning Metals

4.1. Pyrometallurgical refining methods

4.2. Physical refined methods

Adjustion
Crystallization
Vacuum refining

5. Processing of sulfide materials.

Separation melting.
Converting mattes.

6. Metallurgical slags.

The structure of slag melts

In in e d e n and e

The theory of metallurgical processes is a physical chemistry describing the behavior of chemically reacting systems at high temperatures, ranging from 800 to 2500 k and more.

The accelerated progress of mankind began after people learned to use metals. The level of the country and is currently largely determined by the level of development of metallurgical, chemical and mining industries. Currently, extensive development paths have been practically exhausted and the question of the intensive development of all industries, including metallurgy, faced the first place. The last decatheses are characterized by qualitatively new approaches to all production processes, this is:

energy - and resource saving,
deep processing of raw materials and man-made waste,
using the latest achievements of science in production,
use of micro and nanotechnology,
automation and computerization of production processes,
minimize harmful value on the environment.

Listed (and many others) requirements impose high demands on the level of fundamental and special training of a modern engineer.

The proposed tutorial on the theory of metallurgical processes is an attempt to present discipline on the first, the lowest level of complexity, i.e. Without mathematical evidence, with the minimum substantiation of the initial provisions and analysis of the resulting results. The manual consists of 6 chapters covering almost the entire process of obtaining metals from ores and concentrates.

First, let the domain process of smelting iron from iron ore or iron ore concentrates from the school year of the chemicals are remembered. Three phases exist in the blast furnace:

gas phase consisting of gases Co, CO 2, vapors of metals and oxides,
The slag phase consisting of molten oxides Cao, SiO 2, Al 2 O 3, FEO, MNO, etc.
The metal phase consisting of liquid iron and dissolved in it impurities, such as carbon, manganese, silicon, phosphorus, sulfur, etc.

All three phases interact with each other chemically and physically. Iron oxide is restored in the slag phase and transit to the metal phase. Oxygen dissolved in the Slag phase passes into the metal phase and oxidizes impurities in it. The drops of oxides float in the metal phase, and the metal drops are settled in the slag phase. The transition of components from one phase to another is associated with the transfer of them through the borders of the phase partition, therefore the engineer  Metallurg works with multicomponent, heterogeneous, chemically reacting systems.

Currently, metallurgy receives about 70 metals, which are usually divided into colored and black. The latter includes 4 metal: iron, manganese, vanadium and chrome. A group of non-ferrous metals is more numerous, so it is divided into the following subgroups.

Heavy: copper, lead, zinc, nickel, tin, mercury, only 18 elements.
Easy metals: aluminum, magnesium, titanium, silicon, cloth and tick-earth metals, only 12 elements.
Noble: gold, silver, platinum, etc. There are only 8 elements, they received their name due to the lack of affinity for oxygen, therefore in nature are in the free (non-oxidized) state.
Rare metals: refractory - 5 elements, rare-earth - 16 elements and radioactive - 16 elements.

According to the method of production, the processes of production of metals are divided into three groups:

pyrometallurgical

hydrometallurgical I.

electrometallurgical processes.

The first of them proceed at temperatures of about 1000-2500 to the same components are located in molten and dissolved states.

The second flows in aquatic, less often in organic, solvents, at temperatures of 300 - 600 K. Many hydrometallurgical processes also occur at elevated pressures, i.e. in autoclaves.

Electrometallurgical processes occur on electrodes in both aqueous solutions and salt melts at different temperatures. For example, the electrolysis of the alumina in the cryolit-alumina melt leaks at 1230 K, and the electrolysis of platinum from the aqueous electrolyte - at 330 K.

Raw materials for the production of many metals are, first of all, oxidized ores, of which aluminum, iron, chrome, manganese, titanium, partially copper, nickel, lead are obtained. Of the less common sulfide ores, such metals are obtained as copper, lead, nickel, cobalt, and noble metals. Magnesium, calcium and alkali metals are obtained from chloride ores (from water seas and lakes).

Metallurgical productions have a harmful effect on the environment, namely:

reaction gas emissions, such as CO, SO 2, SO 3, CL, CS 2, and many other gases,
pulp and liquid particles of various majority and composition,
drain of large volumes of industrial water polluting water lines, including drinking water supply.
big reset of excessive, low-value energy, which can be used to heat the greenhouses, etc.

These factors have a negative impact. First of all, the employees of enterprises, as well as to nearby cities and settlements. Therefore, one of the most important tasks of the engineer is the organization and planning of production in such a way as to minimize the harmful effects on the environment. Environmental problems should be in the first place not only in public production, but also in the personal self-restriction of each person, in the form of a complete or partial abandonment of personal transport, from excessive consumption of energy resources, etc.

An approximate assessment shows that a person who gets to work in public transport consumes about an order of magnitude less fuel and oxygen, in comparison with the comfort lovers, traveling alone in a car with an engine working volume into several liters. The future of mankind, as a thinking community, is located on the path of conscious self-employment in the consumption of goods, services and, ultimately energy resources.

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