STABILITY OF THE HYDROGEN ABSORPTION AND DESORPTION PLATEAUS IN LANI5-H .2. EFFECTS OF ABSORBING AND DESORBING LARGE ALIQUOTS OF HYDROGEN

There are several reports in the literature of experimental parameters , such as aliquot size, pressure drive and even hydrogenator volume, c ausing shifts in the measured pressures of the absorption and desorpti on plateaux of metal hydrides. Several models have been proposed to ex plain them, both as microstructural realities and as experimental arte facts. We review these models and conclude that most published experim ental evidence of generic ''large-aliquot'' effects can be qualitative ly explained as artefacts resulting from temperature gradients in the hydride bed. Some new results for LaNi5-H are reported, including an e ffect on plateau length which does not seem to be explainable as an ar tefact. It is predicted that measurements with constant pressure over the sample will avoid artefactual large-aliquot effects.