The hydrogen activation of LaNi5

Changes to the hydridable intermetallic compound LaNi5 and its hydriding behaviour during the first few hydrogen absorption—desorption cycles (activation) have been studied. A number of bulk (manometric hydrogen content measurements, optical microscopy), structural (X-ray and neutron diffraction) and microstructural (scanning and transmission electron microscopy) techniques provide strong evidence that the major part of the observed reduction in hysteresis after activation is due to the formation of extended two-dimensional defects in the alloy. Evidence is presented that these defects also contribute to the observed increase in the rate of hydride formation after activation.