Dense nanometric ZrO₂-Al₂O₃ from spray-pyrolysed powders

Abstract

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°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 α-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° C), in which the predominant phase is a tetragonal ZrO₂-Al₂O₃ solid solution, with a small amount of partitioned γ-alumina. Under these optimum conditions, the crystalline size is 10-20 nm with no evidence of porosity.