Thermodynamics of solid solution of hydrogen in M2C type carbides of vanadium and niobium

Equilibrium hydrogen pressures in the systems V ₂CH ₂ and Nb ₂CH ₂ have been determined at several temperatures in the range 400-650°C. Hydrogen pressure data were treated to obtain various thermodynamic quantities for the solutions of hydrogen in V ₂C and Nb ₂C. It has been found that the enthalpies of the reaction H(S.S.) = {1}/{2}H₂( g) are similar but slightly less endothermic compared to the respective metal hydrogen solid solutions. Entropies of dissolved hydrogen in V ₂C and Nb ₂C are also found to be similar to those of hydrogen in the respective metals.