The kinetics of the hydriding and dehydriding reaction of Mg2Ni and Mg-10 wt % Ni was investigated. The reaction rate at various hydride compositions was measured by the pressure change in a constant volume. In the case of Mg2Ni, at the beginning of the reaction the amount of absorbed/desorbed hydrogen can be expressed by n = k(p0 - peq) (ns - n0), where n is the ratio of H to Mg in the solid, p0 and peq are the initial hydrogen pressure of the system and the equilibrium pressure, and n0 and ns are the values of n at the start of the reaction and a constant around 2, respectively. After a transient period of approximately 1 min, a diffusion-controlled stage took place as dn/dt = k′(p - peq)/t, where p is the pressure at time t. In the case of Mg-10 wt % Ni, throughout a run the absorption/desorption rate was expressed by dn/dt = k″ (p - peq)1.25.
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