| Among many metals the magnesium has excellent hydrogen-storage characteristics except that its hydriding and dehydriding rates are low Many works have been carried but in order to improve the reaction rates of magnesium with hydrogen. But their processes for the sample preparation were energy-consuming and complicated. In this work, to simplify the process of sample preparation, magnesium powder and cobalt powder were mixed in a 2 : 1 atomic ratio and pressed under 5 kbar to cylindrical pellet. The activation of the mixture was completed after about 15 hydriding-dehydriding cycles at about 700K and 25 barH₂The activated mixture absorbed hydrogen of about 2.8 weight percent at about 700K and 25 barH₂. The hydrogen storage capacity did not change until the 50th hydriding-dehydriding cycle. Equilibrium plateau pressures appeared at two different pressures, for example at 698K, 9 bar and about 14.5 bar. Under hydrogen pressures of relatively small deviations from the equilibrium plateau pressure, the hydriding reaction rates were controlled by the nucleation. After nucleation they were controlled by Knudsen flow and ordinary gaseous diffusion. Dehydriding reaction rates were controlled by the transformation of hydide into hydrogen and α-solid solution of Mg and Co. |
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