STRUCTURAL STUDIES OF AL-BASED POWDERS PREPARED BY CHEMICAL METHODS

Finely dispersed metal powders have been obtained after chemical reduction of Ni and Co acetylacetonate by lithium aluminum hydride in tetrahydrofuran at low temperature. The Al/Ni and Al/Co stoichiometry of the as-reduced powders was 1.1 and 1.2, respectively. The structure and thermal stability of the as-reduced powders were affected by the temperature of reduction. For the NiAl powders it was found that the thermal treatment initially induces a separation of highly unstable Ni(Al) and Al(Ni) solid solutions, which subsequently react to give a single NiAl phase of cubic structure not reported in the equilibrium phase diagram. Conversely, the reduction of cobalt acetylacetonate directly gives a cubic metastable phase, from which precipitates some hexagonal form of Co after treatment at 450-degrees-C.