Elements of hydride formation mechanisms in nearly spherical magnesium powder particles

Experiments on a large number of magnesium powders varying in particle size, morphology, purity and surface oxidation have shown that most of these parameters influence the kinetics of the hydride formation. Although no single step in the reaction will in general be rate determining we have in a previous investigation been able to assign a nucleation and growth model to the initial hydriding of an atomized powder. This powder of nearly spherical particles (d ≈ 90 μm) with a thin oxide coating has also been used in this investigation of the nucleation and growth mechanisms. It is found that the nucleation is rate determining in the initial hydriding only and that the growth takes place entirely by interface migration of hydrogen from the particle surface. The pressure-nucleation relation and impurity effects on the ultimate degree of reaction are discussed.