Decrepitation process of a hydride forming material observed by neutron radiography

Abstract

Abstract Hydride-forming materials (HFM) are widely investigated for hydrogen storage, separation and purification, due to their reversible reaction with hydrogen at moderated pressures. These materials are mainly used in powder form and they show a considerable change in cell volume during the reaction with hydrogen (up to 25% for LaNi5). This change can exert significant mechanical stresses upon the container vessel walls. We have been studying this phenomenon by measuring the mechanical strains generated on the wall of a cylindrical vessel during hydrogen absorption/desorption cycling. The complexity of studying the mechanical effects is due to the granulometry, porosity and flowability of the powder material which are affected by the decrepitation phenomenon that the material suffers along the cycles. Neutron imaging has proven to be a useful technique to visualize the evolution of the powder rearrangement inside the reservoir. We have identified some key aspects for understanding the relationship between the degree of compaction of the powder, the geometrical parameters of the reservoir (slenderness, wall thickness, filling level), the equivalent pressure exerted by the material against the reactor walls, as well as the number of cycles.