Characterization of the charging techniques used to introduce hydrogen in aluminum

Aluminum foils and single crystals of varying thickness and purity were charged with hydrogen using gas plasma, electrochemical and chemical methods. The concentrations of hydrogen introduced were monitored by gas extraction and prompt gamma-activation analysis measurements. X-ray diffraction measurements indicated that within experimental error there was either a small lattice contraction or a zero change in lattice parameter after charging. It was found that during cathodic and chemical charging an Al(OH)(3) layer formed on the surface. Extensive experiments revealed that unless the surface layer formed during the charging process was removed, the concentration of H measured with either analysis method was erroneously high. The plasma charged samples do not form an Al(OH)(3) layer on the surface, but instead form H-vacancy complexes at the surface which diffuse into the volume and then cluster to form H-2 bubbles. The structure of the hydrogen solutes introduced by the charging methods is discussed and the diffusivity of a hydrogen-vacancy complex at 300 K is estimated. (C) 2002 Elsevier Science B.V. All rights reserved.