Dense nanometric ZrO<SUB>2</SUB>-Al<SUB>2</SUB>O<SUB>3</SUB> from spray-pyrolysed powders

Powders of ZrO2-Al2O3 synthesized by spray pyrolysis of aqueous solutions of nitrates have been subjected to high-pressure rapid-heating compaction at 700-900&#176;C. The original amorphous phase undergoes decomposition during heat treatment via a series of metastable crystalline solid solutions to the equilibrium phases of monoclinic ZrO2 and &#945;-alumina. The application of high pressure results in a substantial decrease in the temperature required for each transformation. Maximum densification during pressure-assisted sintering appears to occur at the lowest temperature (700&#176; C), in which the predominant phase is a tetragonal ZrO2-Al2O3 solid solution, with a small amount of partitioned &#947;-alumina. Under these optimum conditions, the crystalline size is 10-20 nm with no evidence of porosity