It was found that the kinetics of H absorption and desorption were much faster in samples which contained Al2O3 precipitates than in pure Pd or in non-oxidized Pd-3%Al alloy. This was attributed to the presence of a fine micro-crack network which accompanied H absorption in the oxidized alloys. After incomplete oxidation, the isotherms which were measured at 323K corresponded to those for a sample that consisted of material which was depleted of Al (that is, Pd) and material which was non-oxidized (3%Al alloy). After oxidation (1273K, 24h), the latter disappeared and the resultant isotherm for a metal matrix which contained Al2O3 precipitates corresponded very closely to that for pure Pd. The H absorption isotherms clearly showed that internal oxidation occurred via the progressive inward movement of an internal oxidation zone. The measured isotherms, and optical measurements of interface penetration, permitted the degree of interface penetration to be calculated. It was noted that the progression of internal oxidation obeyed parabolic kinetics. The O permeabilities were found to be much higher in Pd-Al2O3, than in pure Pd, although the activation energies were comparable. On the basis of the measured penetration rates at 4 temperatures, the activation energy for O permeability was deduced to be 210kJ/mol.

H.Noh, T.B.Flanagan, R.Balasubramaniam, J.A.Eastman: Scripta Materialia, 1996, 34[6], 863-8