Nanocrystalline NiO and NiO-Ni(OH)2 composite powders prepared by thermal and mechanical dehydroxylation of nickel hydroxide

Nanocrystalline NiO and nanocomposite NiO-Ni(OH)(2), in the form of ultrafine powders, were prepared from NI(OH)(2) by thermal and mechanical dehydroxylation respectively. The powders were characterized by X-ray diffraction, differential scanning calorimetry, secondary electron imaging and transmission electron microscopy. An orientation relationship was observed such that the (0001) planes in the original hexagonal hydroxide structure were parallel to (111)planes in the cubic NiO following thermal dehydroxylation. It is proposed that the crystallographic transformation required for the dehydroxylation process involves the glide of Shockley partial dislocations. It is further suggested that the effect of mechanical grinding is to cause extensive faulting through the glide of Shockley partial dislocations, which lowers the activation energy for dehydroxylation so that the process proceeds at ambient temperature. (C) 1999 Acta Metallurgica Inc.