DENSE NANOMETRIC ZRO2-AL2O3 FROM SPRAY-PYROLYZED POWDERS

Powders of ZrO2-Al2O3 synthesized by spray pyrolysis of aqueous soluti ons of nitrates have been subjected to high-pressure rapid-heating com paction at 700-900 degrees C. The original amorphous phase undergoes d ecomposition during heat treatment via a series of metastable crystall ine solid solutions to the equilibrium phases of monoclinic ZrO2 and a lpha-alumina. The application of high pressure results in a substantia l decrease in the temperature required for each transformation. Maximu m densification during pressure-assisted sintering appears to occur at the lowest temperature (700 degrees C), in which the predominant phas e is a tetragonal ZrO2-Al(2)AO(3) solid solution, with a small amount of partitioned gamma-alumina. Under these optimum conditions, the crys tallite size is 10-20 nm With no evidence of porosity. (C) 1998 Elsevi er Science B.V.