Abstract
Powder samples of three binary Mg-Ni alloys and one ternary Mg-Ni-Mm alloy were electrochemically hydrided and subjected to the temperature-programmed desorption technique. The powders were prepared by mechanical grinding of appropriate as-cast alloy ingots. The alloy samples were hydrided in a 6 M KOH solution at 80 °C for 240 min and at 20 mA g^–1. The structures of the alloys were studied using optical microscopy. The phase compositions of the samples were determined by X-ray diffraction. The formation of MgH₂ and Mg(OH)₂ was observed after hydriding in all of the investigated alloys. It was found that the concentration of absorbed hydrogen depends on the eutectic fraction in the structure and on the hydroxide-formation resistance. In contrast, the decomposition temperature of MgH₂ likely depends on the amounts of both alloying elements and magnesium hydroxide. Compared to pure commercial MgH₂, the decomposition temperatures of MgH₂ in the investigated alloys were reduced by more than 200 °C.

Key words
magnesium alloys, rare earth, thermally activated processes

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