THERMODYNAMICS AND EQUILIBRIUM DISSOCIATION PRESSURES IN THE SYSTEM SmH_2-SmH_3

摘要

Equilibrium hydrogen dissociation pressures have been measured as functions of composition and temperature for the SmH_2-SmH_3 system in the range 448 to 623 K. Relative partial molar enthalpies and entropies in the composition region of continuous solid solutions from n = 2 to 2. 5 atoms H/atom Sm have been evaluated from van't Hoff plots. The hydrogen pressures of the transition from cubic to hexagonal samarium hydride have been determined and the relative molar enthalpy and entropy of formation of hydrogen-deficient haxagonal SmH_3 have been calculated . due to the extreme high-purity conditions the hysteresis found in this work is 6. 5 times less than that found in the past. No similarities have been found between the structures of La and Ce trihydrides deviating from the cubic symmetry and the phases observed in the Srn-H system.