Controlled preparation and mechanism study of zirconia-coated hematite particles by hydrolysis of zirconium sulfates.

Zirconia-precursor-coated hematite particles were prepared by hydrolysis of zirconium sulfate in aqueous solution. The as-prepared zirconia-precursor shell was amorphous with a thickness of about several approximately 30 nm that can be controllably achieved by varying the processing parameters and had a composition of Zr(2)(OH)(6)SO(4), which crystallized to tetragonal ZrO(2) after annealing at 700 degrees C. The focus of this work is to investigate in detail the process and to understand the key issues for surface coating in solution. The thermodynamic analysis on hydrolysis of zirconium sulfate was conducted, and a "surface-deposition region" for zirconia coating was suggested in this work. Furthermore, the kinetic study of the process was also described. The hydrolysis could be considered as a pseudo-second-order reaction at 50 degrees C, and the rate constant was calculated to be 0.61 L mol(-1) s(-1). The hydrolysis mechanism of zirconium salt was also interpreted from the viewpoint of structural chemistry. The influence of the surfactants on the coating process was also discussed.