Characterization of the whiskerlike products formed by hydriding magnesium metal powders

The structure of filamentary crystals produced during the hydriding of magnesium powder has been studied in detail. The needles of small dimensions (typically 0.5 μm in diameter) have been identified by electron analytical techniques to be oriented microcrystals of metallic magnesium. Their formation has been ascribed to the melting of localized aluminum impurities within the bulk magnesium to form a liquid eutectic. In the presence of sublimed magnesium vapor and hydrogen (as a carrier gas) a vapor-liquid-solid mechanism operates to produce a rapid unidirectional extension followed by a slower, two-dimensional growth. As a consequence the needle becomes broader at the tip. In addition, the tip is surmounted by a small Mg-Al eutectic aggregate.