| The formation of magnesium hydride by the reaction of high pressure hydrogen (23 to-27 atm) with magnesium and Mg-25Al alloy powdered was studied in the temperature range of 346℃ to 400℃. And reaction products were identified by using a X-ray diffractometer. For both magnesium and Mg-25Al alloy, hydride phase formed was found to exist in the form of MgH₂ only. Yields (weight percent of magnesium reacted) were increased with the decrease of average particle size of the sample, and were much higher for Mg-25Al Alloy than for magnesium. Decompositions of magnesium hydride and Mg-25Al alloy hydride were also carride out under the dynamic argon atmosphere using a thermogravimetric technique, in the temperature range of 287℃ to 397℃. In both cases, the reaction rates of the initial stage were controlled by the chemical reaction at the interface. The rate equation for the initial stage was expressed, in terms of the fraction decomposed X and reaction time t, as 1-(1-X)=k·t. The apparent activation energies for the decomposition reactions of magnesium hydride and Mg-25Al alloy hydride were 19.5 Kcal/mole and 15.9 Kcal/mole, respectively. And the activation energies for the dehydriding reactions in Mg-Al alloys were considered to decrease with aluminum content. |
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