Thermodynamic stability of barium thorate, BaThO3, from a Knudsen effusionstudy

The Gibbs energy of formation of barium thorate was determined using the Kn udsen effusion forward collection technique. The evaporation process could be represented by the equation BaThO3(s) = ThO2(s) + BaO(g) The vapour pressure of BaO(g) over the two-phase mixture of BaThO3(s) and T hO2(s) was obtained from the rate of effusion of BaO(g) and could be repres ented as ln(p/Pa) (+/-0.39) = - 50526.5/T/K + 26.95 (1770 less than or equal to T/K less than or equal to 2136) The Gibbs energy of formation of BaThO3(s) could be derived from this data and represented as Delta(f)G degrees(BaThO3(s))/kJ mol(-1)+/-8.0 = - 1801.75 + 0.276T/K (C) 19 99 Elsevier Science S.A. All rights reserved.