Formation Mechanism of Hydrous‐Zirconia Particles Produced by Hydrolysis of ZrOCl2 Solutions

The secondary particle size of hydrous‐zirconia fine particles that have been produced by the hydrolysis of various ZrOCl 2 solutions, with and without the addition of NH 4 OH or HCl, was measured using transmission electron microscopy to investigate the effects of the H+ and Cl−ion concentrations on the formation of secondary particles. The average secondary particle size of hydrous zirconia increased as the H+ion concentration increased, attaining a maximum of 200 nm at an H−ion concentration of 0.44 moldm‐3. Further increases in the H+ion concentration then caused a decrease in the average particle size. The present experimental results revealed that the secondary particle size of hydrous zirconia is controlled primarily by the concentration of H+ ions that are produced during hydrolysis. The formation mechanism for the secondary particles in hydrous zirconia was determined on the basis of the present experimental results.