Patent ID: 7201789

Claim:
A process for preparing a composite of nanocrystalline structure based on magnesium and at least one or several other elements or compounds known to absorb hydrogen and to be very few miscible with magnesium or its hydride during grinding, characterized in that it comprises: a) subjecting magnesium or a magnesium-based compound known to absorb hydrogen, to a hydrogenation in order to obtain a hydride in the form of a powder; b) mixing the so-obtained hydride in a powder form with the other element(s) or compound(s) or with a hydride of said other element(s) or compound(s) to obtain a mixture; c) subjecting the so-obtained mixture to an intensive mechanical grinding in order to obtain a composite of nanocrystalline structure in the form of a hydride with an average crystal size between 0.1 nm and 100 nm; and, if required, d) subjecting the composite obtained in step c) to a hydrogen desorption, with the proviso that said other element(s) or compound(s) or their hydride(s) is not Mg 2 NiH 4 .