A THERMODYNAMIC STUDY OF THE THORIUM-HYDROGEN SYSTEM AT 700 K

The partial enthalpies of solution of hydrogen in thorium-hydrogen alloys with H/Th ratios ranging from 0 to 2 have been measured calorimetrically at 700 K. From these data the authors calculate the standard enthalpy of formation of ThH//2 at this temperature to be minus 34. 8 kcal mol** minus **1 with an estimated uncertainty of plus or minus 0. 2 kcal mol** minus **1. This agrees well with values calculated by earlier investigators from plateau pressure equilibrium data. For several alloy compositions within the nearly stoichiometric phase ThH//2 the equilibrium pressures of hydrogen also were determined. Comparisons of the relative partial Gibbs energies of hydrogen obtained from these equilibrium pressures with corresponding enthalpies from calorimetry provide information on the partial entropy.