HYDROGEN UPTAKE OF PALLADIUM-GOLD ALLOYS STUDIED BY AU-197 MOSSBAUER-SPECTROSCOPY

Hydrides of Pd0.99Au0.01 and Pd0.90Au0.10 alloys were prepared electrolytically or under pressures of hydrogen gas up to 7.2 GPa and studied by Mossbauer spectroscopy with the 77 keV gamma-rays of Au-197. The observed isomer shifts show that in Pd0.99Au0.01Hx the interstitial sites next to the gold atoms become occupied by hydrogen only at x greater than or similar to 0.95. The isomer shifts observed at x less than or similar to 0.95 are attributed to volume expansion and long range electronic effects. This interpretation is supported by the volume dependence of the Au-197 isomer shift in Pd0.99Au0.01Hx measured at pressures up to 6 GPa. In Pd0.90Au0.10Hx, hydrogenation at temperatures around 325-degrees-C was found to cause the formation of goldrich zones.