Gibbs free energies of formation of ZnAl2O4 and ZnCr2O4

Jacob, K. T. (1976) Gibbs free energies of formation of ZnAl2O4 and ZnCr2O4 Thermochimica Acta, 15 (1). pp. 79-87. ISSN 0040-6031

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The standard free energies of formation of zinc aluminate and chromite were determined by measuring the oxygen potential over a solid CuZn alloy, containing 10 at.−% Zn, in equilibrium with ZnO, ZnAl2O4+Al2O3(χ) and ZnCr2O4+Cr2O3, in the temperature range 700–900°C. The oxygen potential was monitored by means of a solid oxide galvanic cell in which a Y2O3ThO2 pellet was sandwiched between a CaOZrO2 crucible and tube. The temperature dependence of the free energies of formation of the interoxidic compounds can be represented by the equations, Zn)(wurtzite)+Al2O3(α)→ZnAl2O4(sp) ΔG°=–10,750+1.57T(±150)cal ZnO(wurtzite)+Cr2O3(s)→ZnCr2O4(sp) ΔG°=–15,000+2.05T(±150)cal The heat of formation of the spinels calculated from the measurements by the “Second Law method” is found to be in good agreement with calorimetrically determined values. Using an empirical correlation for the entropy of formation of cubic spinel phases from oxides with rock-salt and corundum structures and the measured high temperature cation distribution in ZnAl2O4, the entropy of transformation of ZnO from wurtzite to rock-salt structure is evaluated.

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Deposited On:17 Oct 2012 11:04
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