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Thermodynamic stability of kΒ-alumina

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Abstract

The activity of K2O in a mixture of α-alumina and KΒ-alumina has been determined using the solid state galvanic cell: ' Ta, Bi-5 mol pct K // α-alumina + KΒ-alumina // In + In2O3, Ta in the temperature range 600 to 1000 K. The cell is written such that the right hand electrode is positive. The solid electrolyte consisted of a dispersion of a-alumina (~15 vol pct) in a matrix of KΒ-alumina. The emf of the cell was found to be reversible and to vary linearly with tem-perature. From the emf and auxiliary data on In2O3 and K2O from the literature, the activity of K2O in the two-phase mixture is obtained as log aK 2O = 2.368 -20,850/T(K) (±0.015) The standard free energy of formation of KΒ-alumina from component oxides is given by K2O (s) + 9.5 α-Al2O3 (s) → K2O.9.5A12O3 (s) δG‡ = -398,920 + 45.01 T(K) (±1000) J mol-1

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Kale, G.M., Jacob, K.T. Thermodynamic stability of kΒ-alumina. Metall Trans B 20, 687–691 (1989). https://doi.org/10.1007/BF02655926

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