Characterisation of the properties of bubbles in the aluminium hydrogen system using SANS and USANS techniques

Full text: Aluminum foils of 98.6 and 99.99% purity were charged with hydrogen using a gas plasma method, resulting in the introduction of a large amount of hydrogen. X-ray diffraction measurements indicated that within experimental error, there was a zero change in lattice parameter after plasma charging. This result indicates that hydrogen does not enters the lattice interstitially, but instead forms an H-vacancy complex at the surface which diffuses into the volume. Inelastic neutron scattering (INS), and transmission and scanning electron microscopy (TEM and SEM) results show that the H-vacancy complexes cluster together to form H2 bubbles. The nature and agglomeration of the bubbles were studied using ultra small angle and small angle neutron scattering (USANS and SANS) technique. The USANS and SANS results indicated scattering from a wide range of bubble sizes from < 2nm up to micron size. SEM and TEM measurements revealed the existence of bubbles on the surface, as well as in the bulk and inelastic neutron scattering experiments show that most of the hydrogen is in the form of H2 molecules. Precision density measurements were used to determine the volume concentration of vacancy sites, and this result was compared with that calculated from the SANS and USANS experiment. The pressure of H2 in a bubble of average volume, the lattice expansion and the number of vacancies per hydrogen were calculated from the SANS and USANS data, and these results are compared to the parameters determined from experiment