Journal of the American Ceramic Society, Vol.88, No.10, 2894-2896, 2005
Thermodynamic stability of potassium-beta-alumina
The thermodynamic stability of K-beta-Al2O3 (KBA) has been determined by characterizing the equilibrium between K-beta- and K-beta"-Al2O3 using a potentiometric technique with yttria-stabilized zirconia (YSZ) as solid electrolyte. The cell Au vertical bar O-2, CO2, K2CO3(Au)vertical bar KBA(Au)vertical bar YSZ vertical bar O-2, (CO2), Pt vertical bar Au allows an in situ check of the establishment and maintenance of the phase equilibrium by changing the composition of the KBA material reversibly. The activity of the potassium oxide dissolved in KBA amounts to (375 degrees-600 degrees C) 1g a(K2O)(beta+beta")= -20000 +/- 500 / T(K) + 5.7 +/- 0.7 from which the standard Gibbs free energy of formation of K-beta"-Al2O3 can be obtained as Delta(f)G degrees(KA15O8)(J/mol) = -4560000 +/- 3000 + (886 +/- 4)T(K).