Factors affecting the particle size of powders synthesised by mechanochemical processing

This paper presents the results of an investigation into the effect of process variables on the average particle and crystallite size of ZrO2 powders synthesised by mechanically activated reaction of anhydrous ZrCl4 with MgO and Li2O exchange reagents. The average particle and crystallite size of the ZrO2 powder formed from the ZrCl4 + 2MgO reaction system was only affected to a significant degree by the duration of milling. Increasing the milling time from 10 minutes to 6 hours decreased the average particle size from approximately 11 to 5 nm. In contrast, the average particle and crystallite size of ZrO2 powder formed by the ZrCl4 + 2Li(2)O reaction system was found to depend on both the milling duration and the presence of inert LiCl diluent. For a given milling duration, the addition of diluent decreased the average crystallite size and increased the proportion of single crystal particles. The effect of milling time was found to depend on the presence of LiCl diluent. The crystallite size of the ZrO2 product formed by the undiluted reactant system was found to be independent of the milling time whilst increasing the milling time of the diluted reactant mixture yielded ZrO2 powders with a reduced crystallite size. The difference in behaviour between the MgO and Li2O systems is attributable to the significantly higher enthalpy change associated with the Li2O system, which allowed crystal growth during reaction.