Vaporization behavior and Gibbs energy of formation of Rb2ThO3

The thermodynamic stability of rubidium thorate, Rb2ThO3(s), was determined from vaporization studies using the Knudsen effusion forward collection technique. Rb2ThO3(s) vaporized incongruently and predominantly as Rb2ThO3(s)=ThO2(s) + 2Rb(g) + 1/2 O2(g). The equilibrium constant K=pRb2·pO21/2 was evaluated from the measurement of the effusive flux due to Rb vapor species under the oxygen potential governed by the stoichiometric loss of the chemical component Rb2O from the thorate phase. The Gibbs energy of formation of Rb2ThO3 derived from the measurement and other auxiliary data could be given by the equation, ΔfG°(Rb2ThO3,s)=−1794.7+0.42T ± 5.0 kJ mol−1 (1058⩽T/K⩽1187).