Thermochemical Description of the Ternary Iron-Nickel-Sulfur System

Abstract

A general approach combining experimental measurements of Gibbs energy and phase equilibria, thermodynamic modelling of phases and calculation of phase diagrams is used to study the ternary Fe–Ni–S system. A quasi-subregular model is used to describe the thermodynamic properties of the metal alloy phases at high temperatures, a statistical thermodynamic model for the monosulfide phase, an associated solution model for the metal-sulfur liquid and the disulfide phase is treated as a pseudo binary solid solution. Values of the solution parameters were obtained using thermodynamic and phase equilibrium data obtained in our own laboratory at Wisconsin as well as those reported in the literature. Agreement between the calculated and experimental values are quite good. Using the thermodynamic values for the phases, phase diagrams of the Fe–Ni–S system were calculated from the liquid phase down to 1173 K. A set of phase diagrams is presented as well as stability diagrams. Phase diagrams at temperatures lower than 1173 K were not calculated since there are not sufficient data to describe the thermodynamic properties of the (Fe, Ni)₄S₃, or (Fe, Ni)₃S₂, phase.