Preparation of mixed fine Al2O3-HfO2 powders by hydrothermal oxidation

Mixed Al2O3-HfO2 powders were prepared by hydrothermal oxidation of the intermetallic compound HfAl3 and the mixture HfAl3-4Al at 4000 to 7000C under 100 MPa. Monoclinic HfO2 with particle sizes of 10-20 nm was finely dispersed among the α-Al2O3 with sizes ranging from nanometers to micrometers. The temperature-time dependence of the reactions of Al, HfAl3, and HfAl3-4Al with H2O was examined. The hydrothermal oxidation mechanism of the compound HfAl3 was different from those of Hf and Al metals. The mixture with fine precipitation of HfAl3 among the Al matrix is supposed to be effective for the preparation of mixed Al2O3-HfO2 powders