Samples of Pd0.97Al0.03 and (Pd0.9Pt0.1)0.97Al0.03, internally oxidized at 1073K for 72h, were submitted to 3 sorption-desorption cycles at 313K by using an electrochemical hydrogen permeation technique. X-ray diffraction revealed the formation of PdO2 only in the case of Pd0.97Al0.03. For (Pd0.9Pt0.1)0.97Al0.03, there was no indication of internal oxidation of the alloying elements after annealing at 1073K for 72h. Transmission electron microscopy of heat-treated Pd0.97Al0.03 revealed dispersed nanoprecipitates of Al2O3 which had coherent interfaces with the Pd matrix. In heat treated (Pd0.9Pt0.1)0.97Al0.03, areas which were rich only in Pt and Al were observed; suggesting the formation of PtAl clusters. In Pd0.97Al0.03, due to the presence of Al2O3 and PdO2, the hydrogen diffusivity (2.3 x 10-12m2/s) was very low in comparison to that in (Pd0.9Pt0.1)0.97Al0.03 (1.0 x 10-11m2/s) and in heat-treated pure Pd (5.5 x 10-11m2/s). The hydrogen solubility in heat-treated Pd0.97Al0.03 was quite high (1075molH/m3) due to the appearance of new interfaces which trapped hydrogen. A low value of hydrogen solubility in (Pd0.9Pt0.1)0.97Al0.03 (136molH/m3) was attributed to non-oxidation of the constitutent elements.

Effects of Internal Oxidation on the Hydrogen Permeation in Pd0.97Al0.03 and (Pd0.9Pt0.1)0.97Al0.03 Alloys. V.M.Azambuja, D.S.Dos Santos, L.Pontonnier, S.Miraglia, D.Fruchart: Journal of Alloys and Compounds, 2002, 346[1-2], 142-6

Table 141

Parameters for H Diffusion in Pd-Au at 273 to 360K