Study of change in packed bed state of nano-structured FeTi hydrogen storage alloy

The volume of metal hydride packed bed changed by the influence of the expansion during hydrogen absorption and by the contraction during hydrogen desorption was measured by direct observation. The metal hydride used in the experiment are newly developed nano-structured FeTi (n-FeTi) by mechanical alloying. In the authors' previous study of LaNi5, the volume of the packed bed gradually increased according to the hydrogen absorption and desorption cycles because of the influence of particle breakup. On the other hands, in n-FeTi produced by mechanical alloying, particle breakup hardly occurred, and the volume of the whole packed bed decreased according to the hydrogen absorption and desorption cycles. Then, the volume change of the whole packed bed due to hydrogen absorption / desorption was small, and the expansion ratio was 5% or less. The porosity data of the metal hydride packed bed obtained in this experiment is considered to be useful for numerical analysis of n-FeTi and design of practical hydrogen tanks.