Kinetics of the reaction between MgNi alloys and H₂

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 - p_eq) (n_s - n₀), where n is the ratio of H to Mg in the solid, p₀ and p_eq are the initial hydrogen pressure of the system and the equilibrium pressure, and n₀ and n_s 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 - p_eq)/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 - p_eq)^1.25.