The kinetics and the time dependence of the reaction between the Mg-23.3%Ni alloy and hydrogen and of the deactivation of the alloy are presented. The Mg-23.3%Ni alloy, which is a eutectic compound of magnesium and Mg2Ni, has the lowest melting point (507 °C) of the MgNi alloys. The rate of the reaction between the Mg-23.3%Ni alloy and hydrogen, which was measured by a constant-volume method, was expressed by the equation dn dt = k(P - Peqn where n is the hydrogen-to-magnesium ratio, P is the hydrogen pressure, Peq is the equilibrium pressure and k is the rate constant. With regard to the temperature dependence of the rate, the relation between In k and 1 T was not linear and hence the activation energy was not obtained. Prior to each run the hydrided alloy was dehydrided in a vacuum and was then pretreated by introducing a specific amount of hydrogen into the system. The reaction rate decreased with the time elapsed after pretreatment. Normal pretreatment together with full hydriding reactivated the alloy to its original level.
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