Kinetics of the reaction between Mg₂Ni and hydrogen

The reaction between Mg₂Ni and hydrogen was investigated by volumetric method. The reaction was divided into two stages; the initial stage was a very rapid reaction whose rate could not be measured, the later stage was the slower step whose rate was expressed by the equation dn/DT=K′(P-P_eq/t where k′ is the constant, P_eq and P are hydrogen pressures at equilibrium and at time t. The reaction rate of the later stage did not depend upon temperature, content of hydrogen in the alloy, and directions of the reaction, desorption and absorption. The amount of reacted hydrogen, Δn, in the initial stage was expressed by Δn=k(P_o-P_eq)(n_s-n_o where P₀ is the initial hydrogen pressure, n_s is a constant around 4, n₀ is a ratio of H to Mg₂Ni at the initiation of the run, and k is a constant. The apparent activation energy of the reaction was nearly zero. It is considered that the reaction between the alloy and gaseous hydrogen takes place on metallic Mg₂Ni in the initial stage and in the later stage reaction proceeds on the deactivated site.