In this study. mechanochemical processing has been investigated as a means of manufacturing nanoparticulate powders of NiO. Two different reactant mixtures were examined and compared. The first system was based on mechanical milling of Ni(OH)(2) with NaCl diluent. Milling of this reactant mixture resulted in disintegration of the Ni(OH)(2) precursor and its progressive dispersal into the NaCl matrix. Subsequent heat treatment and washing yielded a nanocrystalline powder of NiO, which contained a significant proportion of particles with an unusual platelike morphology. The second system that was examined was based on mechanically activated reaction of NiCl2 + Na2CO3 + 4NaCl. Milling resulted in mixing and microstructural refinement of the reactant mixture. Chemical reaction during post-milling heat treatment resulted in the formation of a powder consisting of nanocrystalline NiO grains embedded in NaCl. Removal of the NaCl by washing with water yielded NiO nanoparticles with an equiaxed particle shape. (C) 2009 Elsevier B.V. All rights reserved.