Changes in the Properties of Ultrafine Al2O3-ZrO2-Y2O3-CeO2 Powders After Heat Treatment in the Range 400-1450°C

Ultrafine 90AZK, 80AZK, 70AZK, and 58.5AZK powders in the Al2O3-ZrO2-Y2O3-CeO2 system were produced for the first time by a combined method involving hydrothermal synthesis followed by mechanical mixing with alpha-Al2O3 (HTSM). The properties of the powders heat treated in the range 400-1450 degrees C were examined by differential thermal analysis, X-ray diffraction, electron microscopy, and nitrogen thermal adsorption-desorption (BET). The sizes of primary particles were calculated with the Scherrer equation. The AMIC (Automatic Microstructure Analyzer) software was applied to process the powder morphology analysis results. The F-ZrO2 -> T-ZrO2 phase transformation was found to proceed completely when the powders were mechanically mixed in the HTSM process. The M-ZrO2 phase was identified as traces in the ultrafine 90AZK and 80AZK powders after mechanical mixing, was not found in the 70AZK powder, and emerged as traces in the 58.5AZK powder above 1150 degrees C. Heat treatment was shown to induce a topochemical memory effect in the ceramics: the morphology and shape factor of the ultrafine powders following heat treatment at 400-1450 degrees C varied topologically continuously. The dependence of primary particle sizes and specific surface area of the powders on the heat treatment temperature indicated that they had high sintering activity. The powders are needed to produce highly efficient ZTA composites in the Al2O3-ZrO2-Y2O3-CeO2 system, consisting of fine particles of the viscous zirconia-based solid solution, codoped with ceria and yttria, distributed in a rigid alumina matrix.