Nucleation and Growth for Synthesis of Nanometric Zirconia Particles by Forced Hydrolysis

Abstract

Monodispersed nanoscale metal oxide powders are important precursors for the preparation of advanced ceramics with uniform nanostructures and properties. Hydrous zirconia particles in nanometer dimensions were synthesized via forced hydrolysis, that is, homogeneous hydrolysis and controlled hydrothermal polymerization/condensation of zirconium tetramers in aqueous solutions of zirconyl inorganic salt. This thermohydrolytic route uses inexpensive starting chemicals—that is, inorganic metal salt, which makes the forced-hydrolysis approach more competitive than other sol–gel routes using metal alkoxides. Hydrothermal treatment of zirconyl salt solutions (0.01 to 0.075 M) produced nanocrystalline monoclinic ZrO2powder with a narrow size distribution. The hydrous zirconium oxide particles are somewhat porous, cube-shaped aggregates of small crystallites (< 5 nm). The nucleation and nanoparticle growth in zirconyl chloride aqueous solutions (100°C) was successfully monitored with a custom-designed, low-power dynamic laser light-scattering spectrophotometer. Extensive experimental evidence strongly supports the position that particle growth is mainly via an aggregation mechanism. On the other hand, the growth kinetics are controlled by the coupled events involving polymerization/condensation and colloidal coagulation. Both the controlled-reaction and the controlled-aggregation approaches were studied to reduce the induction period for nucleation as well as to enhance particle growth kinetics. The present study of the synthesis process and the characterization of nanosize powders constitute prerequisite steps for fabrication of dense, nanophase zirconia materials (with grain size on the order of 1 to 100 nm) that are expected to have improved mechanical and thermomechanical stability at elevated temperatures.