# Phase Equilibria, Oxygen Potentials, and Activities in the System Ni-Co-Si-O at 1373 K

Jacob, Thomas K and Seetharaman, Seshadri (1996) Phase Equilibria, Oxygen Potentials, and Activities in the System Ni-Co-Si-O at 1373 K. In: Journal of the American Ceramic Society, 79 (11). pp. 2815-2820.

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## Abstract

In the system Ni-Co-Si-O, the compositions of coexisting phases participating in two-phase equilibria between the monoxide $(Ni_yCo_{1-y}O)$ and orthosilicate $(Ni_zCo_{1-z}Si_{0.5}O_2)$ crystalline solutions, and alloy $(Ni_xCo_{1-x})$ and orthosilicate phase, have been determined at 1373 K. The samples were equilibrated at 1373 K under argon gas, and the equilibrium compositions of the phases present after quenching were measured by electron probe microanalysis (EPMA). A solid-state cell incorporating yttria-stabilized zirconia as the solid electrolyte was used to measure the oxygen chemical potential corresponding to the three-phase equilibrium between the alloy, orthosilicate solution, and quartz as a function of alloy composition. From these measurements, activity-composition relationships in the alloy and orthosilicate solid solutions have been derived using a new method. Activities in the silicate solution have also been obtained independently using the mixing properties of the rock-salt solid solution available in the literature and the tie-line information obtained in this study. Both methods yield almost identical results. All three solid solution series-alloy, monoxide, and orthosilicate-exhibit mild positive derivations from ideality. The excess Gibbs free energy of mixing of the orthosilicate solid solution $(Ni_zCo_{1-z}Si_{0.5}O_2)$ at 1373 K can be represented by the relation $\Delta GE=(2110 \pm 30)^.z(1-z) J^. mol^{-1}$

Item Type: Journal Article Copyright of this article belongs to John Wiley and Sons. Division of Chemical Sciences > Materials Research CentreDivision of Mechanical Sciences > Materials Engineering (formerly Metallurgy) 31 Aug 2007 10 Jan 2012 05:45 http://eprints.iisc.ernet.in/id/eprint/10804