Phase stability in binary palladium alloys

The phase equilibria of ordered phases in Pd-Me binary systems (where Me = Co, Rh, Ir, Cu, Ag, Au, Ni, or Pt) are analyzed, so as to find correlations among the crystal-chemical and crystal-geometric factors. The packing coefficient for disordered solid solutions in such palladium-based binary systems is close to 0.74, against the background of slight deviation of the atomic volume from Zen’s law. The increase in the hydrogen permeability in Cu-Pd binary alloys is found to correlate with considerable decrease in the packing coefficient for ordered B2 phase close to 40 at % Pd. In Pd-Me binary systems, with certain combinations of temperature and dimensions, different structural and phase states are formed. When the results are plotted in coordinates of the temperature factor and the dimensional factor, three regions are seen. On that basis, the structural and phase states may be classified as a function of the ratio between the temperature and dimensional factors in palladium-based binary systems. Region I corresponds to systems that only form solid solutions; region II to systems where ordered phases are formed from the solid solution; and region III to compounds in which the solid solutions are stratified.