THERMODYNAMICS OF TERNARY SYSTEMS MgO-Fe0-Si02 AND MgO-Fe0-Ca0 AT 1000 K

Abstract

Several natural and technological reactive and non-reactive multi-component systems such as slags encountered in different metal extraction or refining processes, refrac-tories and building materials, dispersed phases of composite materials and molten magma, the parent rock material of the earth's crust constitute oxides like FeO, MgO, CaO, Si02 etc. Mutual interactions controlling the chemical reactivity and equilibrium phase assemblages among oxides, therefore, control the different slag-metal reactions involved in metal extrac-tion and refining, behaviour of different type of refractories and mineralisation of rocks formed. Thermodynamic properties of oxide and silicate systems have, therefore, been exten-sively studied by metallurgists, materials scientists, geolo-gists, ceramists and chemists. The ternary systems MgO-Fe0-Si02 and MgO-Fe0-Ca0 and their corresponding binaries have special relevance to ferrous metallurgy. A survey of available literature reveals that although the binary Fe0-Mg0 and Fe0-Ca0 systems have been extensively studied for determination of thermodynamic pro-perties and analysis of phase equilibria, the ternary systems Fe0-Mg0-Si02 and Fe0-Mg0-Ca0 have mostly been studied for phase equilibria. In the present investigation, therefore, thermodynamic properties of the binary systems Fe0-MgO, Fe0-Ca0 and Fe0-Si02 and the ternary systems Fe0-Mg0-Si02 and Fe0-Mg0- Ca° are studied at 1000 K employing a calcia-.stabilized zirconia solid electrolyte cell, For this purpose, a solid electrolyte cell operated in an inert atmosphere of dry, purified nitrogen, with the following cell scheme was locally. fabricated, Pt/ Fe FeO containing oxide System Zr02)0.85(Ca0)0,15 ff/F Fe° Pt From emf data, values of activity of FeO are calculated at different concentrations for slag samples studied. Using standard thermodynamic relationships, activities of other components and also the de:X4-mix and LGITL are calculated. Emf studies on the system Fe0-8102 permitted the calculation of standard free energy of formation of Fe2SiO4 from its component oxides. Lines of constant activity of Fe0 and other component oxides in different phase regions are drawn for the ternary systems studied. Properties of binary systems FeSiO3- MgSiO3 and Fe2SiO4-Mg2SiO4 are also computed and the values of standard free energy of formation for the compounds "FeSiO3" and Fe2S104 are determined at 1000 K from the emf data on the ternary system MgO-Fe0-Si02. In case of the ternary system MgO-Fe0-CaO, isothermal section of phase dia-gram at 1000 K is drawn. The entire text of the dissertation has been divided into six chapters. Chapter 1 has been devoted to the brief introduction to the problem, critical review of literature comprising of different techniques used to study the thermodynamic proper-ties of alloy, oxide, silicate and other systems with emphasis on solid electrolyte technique, survey of available literature on various binary and ternary oxide and silicate systems and finally formulation of the problem, Chapter 2 deals with the experimental set-up, materials used, sample preparation and technique adopted for experi-mentation for determination of thermodynamic properties of binary and ternary oxide systems. Chapter 3 deals with the experimental results for the binary systems Fe0-MgO, FeO--CaO and Fe0-3i02. Activity and other thermodynamic properties are calculated from emf data and the present results are compared with the relevant data available in literature. Chapter 4 deals with the experimental results far the ternary systems FeO-Mg0-31.02 and FeO7,IMO-Ca0. Thermodynamic properties, calculated from emf data, are presented and com-; pared, wherever possible, with the relevant data in literature. Chapter 5 deals with the discussion of the results on binary and ternary oxide systems. .Results on other similar systems from literature are presented for a comparison. Finally, Chapter 6 lists the major conclusions drawn from the present investigation. Assistance rendered by the technical and laboratory staff, Sarvasri S.R.Kaushik, S.B.Sharma, Rakesh Misra, B.D..Sharma, Abdul Razak and Rishipal during fabrication of experimental set-up and actual runs is also gratefully acknowledged, But 'for the excellent draftsmanship of Sri M.C.Vaish and Sri Atma Prakash and meticulous typewriting of Sri U,K.Mishra and Sri Ram Gopal, the present shape of this thesis could not have been possible. The author expresses his very sidicere appreciation of their efforts, He would also like to record very sincerely and most humbly the continuous encouragement and kind support in all possible ways, he received from his parents during the entire period of research work and preparation of this dissertation. Last, but not the least, the author would also express his sincere gratitude to several other friends and authors of research publications, who made available reprints of the papers not available locally.