Nobuyuki Yanagihara

Life properties of TiMn alloy hydrides and their hydrogen purification effect

The effects of pressure-induced absorption-desorption cycling on the degradation properties and the hydrogen purification ability of TiMn alloy hydrides were studied. The lines in the characteristic X-ray diffraction pattern were much broader and weaker in the cycled alloys but the C14 hexagonal structure was maintained and no second phase was observed. The hydrogen capacity was reduced by 30% for TiMn binary alloy and by 20% for TiMn multicomponent alloys after about 10 000 cycles in contrast with the marked reduction observed for LaNi5. In some cases slight recovery could be produced by heating at 500 °C for 1 h in a vacuum after cycling. Gas chromatography measurements on hydrogen released from TiMn1.5 hydride showed that the hydrogen purity was better than 99.9999% (except for an H2O impurity) after a purge release of only a few per cent of hydrogen when the purity of the commercial grade hydrogen absorbed by the hydride was 99.99%. It can be concluded from the results of these measurements that hydrogen purification using TiMn alloy is related to two factors. The removal of N2, CO and CO2 proceeds by surface poisoning (i.e. oxidation, physisorption or chemisorption), whereas the removal of CH4, O2, H2O and Ar is controlled by surface poisoning and concentration. The hydrogen purification effect of TiMn alloy hydrides showed little degradation even after a large number of absorption-desorption cycles.