Thermal Desorption Spectra of Hydrogen From LaNi sub 5

Thermal desorption of hydrogen from LaNi sub 5 H sub x shows spectra which consist of a single peak for x < = 6 and develop into a two-peak structure for x approx = 6.7. The desorption of H starts at a low temperature of approx 160K and terminates at approx 420K. Analysis of the spectra leads to a conclusion that the rate-determining step of the desorption is a diffusion process for temperatures < approx 175K and either a diffusion or a phase transformation for higher temperatures. This is dissimilar to the PdH sub x system, where the desorption that occurs in the temperature range 150-380K is a surface-controlled process. The activation energy obtained for H desorption from the beta phase of the LaNi sub 5 H sub x system was 32 plus/minus 4 kJ (mol H sub 2 ) exp --1 . 24 ref.--AA