Activities of constituents in metallurgical slags on the basis of Margulesequations

Complex thermodynamic calculations axe contemporarily performed using speci alist computer software. An integral part of such systems are databases wit h thermochemical data. The computer system TERMO, developed at the Chair of Extraction and Recycling of Metals of the Technical University of Czestoch owa, comprises an extensive database containing thermochemical data for sub stances useful in metallurgy, including those for slag solutions. The datab ase contains among other things, data and parameters for such models of the thermodynamic description of slags, as Gaye's model and the regular soluti ons model. These models are used for the calculations of equilibrium states in heterogeneous systems. It has been found based on the experience gained that these models are characterized in certain cases by a little accurate description of the activities of constituents, which is particularly true f or systems with highly diverse interactions in acid slags. Therefore, a pro posal is put forward in this study to represent deviations from ideality (i n binary and ternary slag solutions) using Margules polynomials, as against results obtained using the regular solutions model. The Margules model rel ies on using the expansion of the polynomial of constituent concentrations (up to a specific degree) for the description of the excess free enthalpy o f solution, on the assumption that the expression for G(E) reaches the valu e of zero when the mole fractions of the constituents of that solution are equal to unity. The form of the Margules polynomial should constitute an op timum of the precision of description and the level of its complexity. For the description of the excess free enthalpy of the binary solution, a fourt h-degree polynomial of the following form was employed: G(1-2)(E) = X1X2 (W-1112-X-1 + W1222X2 + W1122X1X2), where: X-1, X-2 - mole fractions of solution constituents, W-ijkl - Margule s parameters fitting the model to experimental data. For the performed calculations fitting the parameters W-ijkl, a uniform ref erence state was adopted for the activities of particular solution constitu ents - in the form of a pure liquid constituent, The calculations concerned the following binary systems: CaO - SiO2, SiO2 - MnO, CaO - FeO and FeO - SiO2, a result of which the parameters W-ijkl and their temperature relatio nships were obtained. Moreover, relationships describing the excess free en thalpies of constituents in the ternary slag FeO - SiO2- CaO were determine d. It has been found on the basis of the analysis carried out that IV-order polynomials can be. used for the description of binary and multi-constitue nt slag solutions more successfully than regular solution models either in their classical formulation or as corrected by S. Ban-ya. The method of pro ceeding for obtaining the parameters of the model based on Margules polynom ials, as presented in this article: will be a basis for the development of a new and alternative variant of thermochemical database for the computer s ystem aiding the caculations of equilibrium states in heterogeneous systems .