NUCLEATION AND GROWTH FOR SYNTHESIS OF NANOMETRIC ZIRCONIA PARTICLES BY FORCED HYDROLYSIS

Monodispersed nanoscale metal oxide powders are important precursors f or the preparation of advanced ceramics with uniform nanostructures an d properties. Hydrous zirconia particles in nanometer dimensions were synthesized via forced hydrolysis, that is, homogeneous hydrolysis and controlled hydrothermal polymerization/condensation of zirconium tetr amers in aqueous solutions of zirconyl inorganic salt. This thermohydr olytic route uses inexpensive starting chemicals-that is, inorganic me tal salt, which makes the forced-hydrolysis approach more competitive than other sol-gel routes using metal alkoxides. Hydrothermal treatmen t of zirconyl salt solutions (0.01 to 0.075 M) produced nanocrystallin e monoclinic ZrO2 powder 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 degrees C) was successful ly monitored with a custom-designed, low-power dynamic laser light-sca ttering spectrophotometer. Extensive experimental evidence strongly su pports the position that particle growth is mainly via an aggregation mechanism. On the other hand, the growth kinetics are controlled by th e coupled events involving polymerization/condensation and colloidal c oagulation. Both the controlled-reaction and the controlled-aggregatio n approaches were studied to reduce the induction period for nucleatio n as well as to enhance particle growth kinetics. The present study of the synthesis process and the characterization of nanosize powders co nstitute prerequisite steps for fabrication of dense, nanophase zircon ia materials (with grain size on the order of 1 to 100 nm) that are ex pected to have improved mechanical and thermomechanical stability at e levated temperatures. (C) 1998 Academic Press.