Abstract
The swelling ability of LaNi5 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. LaNi5 is one of the candidate materials for HSA actuators as well as palladium. Some prototypes of HSA actuators using LaNi5 have been fabricated; however, the kinetic swelling ability of LaNi5 itself has been not investigated. In this paper, the authors investigated the static and kinetic swelling ability of LaNi5 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 LaNi5 was also compared with that of palladium. The results show that LaNi5 swells 1.8 times more than palladium under 0.5 MPa. LaNi5 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.
Highlights
A hydrogen storage alloy (HSA) has a characteristic that its volume increases with absorbing hydrogen
When hydrogen gas is charged into the actuator, it generates displacement and force induced by the swelling of hydrogen storage alloy
The materials in which plastic deformation occurs generally show high pulverization resistance as well as good formability. These requirements are critical because the performance of an HSA actuator is influenced by the hydrogen absorption/discharge characteristics of HSA; the swelling ability of HSA is not included in the requirements
Summary
A hydrogen storage alloy (HSA) has a characteristic that its volume increases with absorbing hydrogen. The materials in which plastic deformation occurs generally show high pulverization resistance as well as good formability These requirements are critical because the performance of an HSA actuator is influenced by the hydrogen absorption/discharge characteristics of HSA; the swelling ability of HSA is not included in the requirements. Investigated the kinetic absorption behavior of palladium powder, and revealed that diffusion of hydrogen atoms is dominant as a rate-determining step during the swelling The information on these static and kinetic swelling characteristics is helpful to select a suitable hydrogen storage alloy in the design of an HSA actuator.
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