Phase equilibria in the system NiO-CaO-SiO2 and Gibbs energy of formation of CaNiSi2O6

Mukhopadhyay, Sukanya and Jacob, KT (1995) Phase equilibria in the system NiO-CaO-SiO2 and Gibbs energy of formation of CaNiSi2O6. In: Metallurgical and Materials Transactions A, 26 (9). pp. 2311-2315.

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Abstract

Phase relations in the pseudoternary system NiO-CaO-SiO2 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 CaNiSi2O6 with clinopyroxene structure. The Gibbs energy of formation of CaNiSi2O6 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 + SiO2 + CaSiO3 + CaNiSi2O6 \ (Y2O3)ZrO2 \ Ni + NiO, Pt From the electromotive force (emf) of the cell, the Gibbs energy of formation of CaNiSi2O6 from NiO, SiO2, and CaSiO3 is obtained. To derive the Gibbs energy of formation of the quaternary oxide from component binary oxides, the free energy of formation of CaSiO, is determined separately using a solid state cell based on single crystal CaF2 as the electrolyte: Pt, O-2, CaO + CaF2 \ CaF2 \ CaSiO3 + SiO2 + CaF2, O-2, Pt The results can be expressed by the following equations: NiO (r.s) + CaO (r.s) + 2SiO(2) (qz) --> CaNiSi2O6 (pyr) Delta G degrees = -115,700 + 10.63T (+/-100) J mol(-1) CaO (r.s) + SiO2 (qz) --> CaSiO3 (wol) Delta G degrees = -90,030 -0.61T (+/-60) J mol(-1).

Item Type:	Journal Article
Publication:	Metallurgical and Materials Transactions A
Publisher:	The Minerals, Metals & Materials Society
Additional Information:	Copyright of this article belongs to The Minerals, Metals & Materials Society.
Department/Centre:	Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	01 Mar 2012 06:26
Last Modified:	01 Mar 2012 06:26
URI:	http://eprints.iisc.ac.in/id/eprint/42690

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