Mechanochemical reaction of anhydrous ZrCl4 With LiOH has been used to synthesize nanocrystalline powders of ZrO2. The mechanism of chemical reaction was found to depend on the presence of LiCl diluent in. the initial reactant mixture. In the absence of LiCl diluent, reaction of the precursors occurred in a combustive manner and resulted in the formation of agglomerated nanoparticles of tetragonal ZrO2 embedded within a matrix of LiCl and LiCl.H2O. Continued milling after the combustion event resulted in a progressive loss of specific surface area and transformation of the tetragonal ZrO2 to the equilibrium monoclinic structure. Dilution of the initial reactant mixture with 4LiCl suppressed combustive reaction. Reaction of the precursors occurred gradually and resulted in the formation of an amorphous ZrO2 gel that crystallized with the tetragonal structure on calcination at 500 degreesC for 1 h. (C) 2002 Elsevier Science Ltd. All rights reserved.