Hydrogen surface interactions on clean and on oxidized polycrystalline aluminium and Al 5083 alloy

The chemisorption of hydrogen on a polycrystalline aluminium surface was studied (at room temperature) using combined measurements of Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and direct recoil spectrometry (DRS). The behaviour of pure aluminium was compared with that of a commercial Al 5083 alloy (containing 4.0% Mg, 0.7% Mn and 0.15% Cr). In both cases it was found that the sputter-cleaned metallic surfaces did not react with hydrogen up to exposures of 1000 L H₂ (1 L = 10^-6 Torr s). Oxidizing the clean surfaces (by pre-exposure to oxygen) induced changes in the observed hydrogen-surface interactions for the Al 5083 alloy, but not for the pure aluminium. A sub-monolayer coverage of oxygen on Al 5083 induced enhanced reactivity towards hydrogen which accumulated on the oxidized surfaces. In contrast, oxidized surfaces of pure aluminium did not display any hydrogen build-up following H₂ exposure. These differences between unalloyed aluminium and Al 5083 were correlated with the different oxidation mechanisms of the corresponding surfaces. The presence of magnesium in the Al 5083 alloy may induce the modified behaviour of both oxidation mechanisms and hydrogen-surface interactions.