# Phase equilibria in the System $NiO-CaO-SiO_2$ and Gibbs Energy of Formation of $CaNiSi_2O_6$

Mukhopadhyay, Sukanya and Jacob, KT (1995) Phase equilibria in the System $NiO-CaO-SiO_2$ and Gibbs Energy of Formation of $CaNiSi_2O_6$. In: Metallurgical and Materials Transactions A, 26A (9). pp. 2311-2315.

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## Abstract

Phase relations in the pseudoternary system $NiO-CaO-SiO_2$ at 1373 K are established. The coexisting phases are identified by X-ray diffraction and energy-dispersive X-ray analysis of equilibrated samples. There is only one quaternary oxide $CaNiSi_2O_5$ with clinopyroxene structure. The Gibbs energy of formation of $CaNiSi _2O_6$ is measured using a solid state galvanic cell incorporating stabilized zirconia as the solid electrolyte in the temperature range of 1000 to 1400 K: Pt, $Ni+SiO_2+CaSiO_3+CaNiSi_2O_6|(Y_2O_3)$ $ZrO_2|Ni+NiO$, Pt From the electromotive force (emf) of the cell, the Gibbs energy of formation of $CaNiSi_2O_6$ from NiO,$SiO_2$, and $CaSiO_3$ is obtained. To derive the Gibbs energy of formation of the quaternary oxide from component binary oxides, the free energy of formation of $CaSiO_3$ is determined separately using a solid state cell based on single crystal $CaF_2$ as the electrolyte: Pt, $O_2$, $CaO+CaF_2|CaF_2|CaSiO_3+SiO_2+CaF_2, O_2,$ Pt the results can be expressed by the following equations: $NiO (r.s)+CaO (r.s)+2SiO_2 (qz)^\rightarrow CaNiSi_2O_6 (pyr)$ $\Delta G= 115,700+10.63T(±100) J mol^{-1}$ $CaO (r.s)+SiO_2 (qz) ^\rightarrow CaSiO_3 (wol)\Delta G°=-90,030-0.61T (+60) J mol^{-1}$

Item Type: Journal Article Copyright of this article belongs to The Minerals, Metals & Materials Society. Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy) 08 Aug 2007 27 Jan 2012 06:25 http://eprints.iisc.ernet.in/id/eprint/11546