Effects of chemical species on the crystallization behavior of a sol-derived zirconia precursor

Abstract

The thermal and crystallization behaviors of a sol-derived zirconia precursor are affected by the chemical species (such as chloride, acetate, and hydroxyl; i.e., Cl -, CH 3COO -, and OH -) present in the solution in which they are aged. The crystallization temperature of zirconia precipitate increases steadily with decreasing pH when hydrochloric acid is added to the aging mother liquor. A more dramatic increase in crystallization temperature is observed when acetic acid is used to reduce the pH of the aging solution. The precursors aged in the solutions of intermediate pH range demonstrate a typical two-step crystallization behavior, due to the transition from a OH --dominated surface structure to a CH 3COO --dominated one. These results show that a higher crystallization temperature results when the OH - groups attached to the surface of precursor particles are replaced by the CH 3COO - groups. Only a slight decrease in the crystallization temperature of aged precipitates occurs when free species, such as CH 3COO - and OH -, are being removed from the aging solution.