Solubility and diffusion of H in ordered (L12) and disordered Pd3Mn

Hydrogen isotherms have been measured from 423 to 573 K for the disordered and L12 ordered forms of Pd3Mn and, from these equilibrium isotherms, ΔHH and ΔSH have been determined over a range of r values where r=H-to-metal, atom ratio. ΔHH values are significantly more negative for the L12 ordered form than for the disordered form. H diffusion constants have been determined for the L12 and disordered forms of Pd3Mn from gas phase H permeation measurements through Pd3Mn membranes (423-573 K). The activation energy for diffusion of H in the L12 form is 35.2 kJ/mol H which is more reasonable than the value of 76.3 kJ/mol H previously reported. The diffusion constant is greater for the disordered than for the L12 form.