Suitability Evaluation of LaNi(5) as Hydrogen-Storage-Alloy Actuator by In-Situ Displacement Measurement during Hydrogen Pressure Change

The swelling ability of LaNi(5) for application to hydrogen-storage-alloy (HSA) actuator is discussed through the measurement of the swelling ratio in hydrogen. The HSA actuator is driven by hydrogen pressure change causing the swelling of HSA. LaNi(5) is one of the candidate materials for HSA actuators as well as palladium. Some prototypes of HSA actuators using LaNi(5) have been fabricated; however, the kinetic swelling ability of LaNi(5) itself has been not investigated. In this paper, the authors investigated the static and kinetic swelling ability of LaNi(5) powder under hydrogen atmosphere. The results showed that the swelling ratio increased by 0.12 at the phase transition pressure. Response time decreased with an increase in the charged pressure during absorption, while it remained constant during discharge. Reaction kinetics revealed that these swelling behaviors were explained by hydrogen absorption and lattice expansion. The swelling ability of LaNi(5) was also compared with that of palladium. The results show that LaNi(5) swells 1.8 times more than palladium under 0.5 MPa. LaNi(5) is suitable for an actuator driven repeatedly under more than the phase transition pressure. Palladium can be used for one-way-operation actuator even under 0.1 MPa since its response time during the evacuation was much longer than during the pressurization.