Phase Equilibria in the System Al2O3-CaO-CoO and Gibbs Energy of Formation of Ca3CoAl4O10

Jacob, KT and Kale, GM and Shekhar, Chander (2009) Phase Equilibria in the System Al2O3-CaO-CoO and Gibbs Energy of Formation of Ca3CoAl4O10. In: Journal of Phase Equilibria and Diffusion, 30 (1). pp. 2-11.

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Abstract

An isothermal section of the system Al2O3-CaO-CoO at 1500 K has been established by equilibrating 22 samples of different compositions at high temperature and phase identification by optical and scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy after quenching to room temperature. Only one quaternary oxide, Ca3CoAl4O10, was identified inside the ternary triangle. Based on the phase relations, a solid-state electrochemical cell was designed to measure the Gibbs energy of formation of Ca3CoAl4O10 in the temperature range from 1150 to 1500 K. Calcia-stabilized zirconia was used as the solid electrolyte and a mixture of Co + CoO as the reference electrode. The cell can be represented as: ( - )\textPt,\textCaAl 2 \textO 4 + \textCa 1 2 \textAl 1 4 \textO 3 3 + \textCa 3 \textCoAl 4 \textO 10 + \textCo//(CaO)ZrO 2 \text// \textCoO + \textCo,\text Pt ( + ). (−)PtCaAl2O4+Ca12Al14O33+Ca3CoAl4O10+Co//(CaO)ZrO2//CoO+Co Pt (+) From the emf of the cell, the standard Gibbs energy change for the Ca3CoAl4O10 formation reaction, CoO + 3/5CaAl2O4 + 1/5Ca12Al14O33 → Ca3CoAl4O10, is obtained as a function of temperature: \Updelta Gr\texto Unknown control sequence '\Updelta'/J mol−1 (±50) = −2673 + 0.289 (T/K). The standard Gibbs energy of formation of Ca3CoAl4O10 from its component binary oxides, Al2O3, CaO, and CoO is derived as a function of temperature. The standard entropy and enthalpy of formation of Ca3CoAl4O10 at 298.15 K are evaluated. Chemical potential diagrams for the system Al2O3-CaO-CoO at 1500 K are presented based on the results of this study and auxiliary information from the literature.

Item Type:	Journal Article
Publication:	Journal of Phase Equilibria and Diffusion
Publisher:	ASM International
Additional Information:	Copyright of this article belongs to ASM International.
Keywords:	chemical potential;electromotive force (emf);enthalpy of formation;entropy;experimental thermodynamics;Gibbs energy; ternary phase diagram
Department/Centre:	Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	29 Dec 2011 05:34
Last Modified:	29 Dec 2011 05:34
URI:	http://eprints.iisc.ac.in/id/eprint/42754

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