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Hydrogen decrepitation of magnesium-rich intermetallics

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2013
Aydınlı, Alptekin
The production of metal hydride canisters may involve mechanical milling of the alloy powders under protective atmosphere and filling them into the canister in a glove-box environment. Such processes are often quite costly, and it is desirable to find a process which does not necessitate the use of protective atmosphere. Hydrogen decrepitation is one such process which involves in-situ pulverization of hydrogen storage alloys. The process starts with coarse alloy powders filled into a canister in open atmosphere and then subjected to several cycles of severe hydrogenation and dehydrogenation treatments which reduce the particles into submicron sizes. Two alloys were selected in the current study; Mg2Ni and Mg2Cu. The alloys were prepared by skull melting in an induction furnace using a cold crucible. Both Mg2Ni and Mg2Cu were melted under high pressure argon atmosphere due to high partial pressure of Mg. Solid alloys obtained in this way were pulverized by crushing them in a mortar and sieved to yield particles within 63-53 μm range. The alloy powders were then subjected to 10 hydrogenation cycles in a custom-made apparatus. Samples from hydrogenation cycles were examined by SEM, laser diffraction and BET analysis techniques so as to follow the decrepitation process. Results showed that Mg2Ni alloy powder was pulverized easily upon cycling reaching to submicron sizes with no more than three hydrogenation cycles. Mg2Cu, on the other hand, was resistant to pulverization. This was despite the fact that the alloy was dissociated upon hydriding to MgH2 and MgCu2 with 24.6% volume expansion.