Changes in the Properties of Ultrafine Al₂O₃ –ZrO₂ –Y₂O₃ – CeO₂  Powders after Heat Treatment in the Range 400–1450 °С

Abstract

Ultrafine 90AZK, 80AZK, 70AZК, 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 α-Al₂O₃ (HTSM). The properties of the powders heat treated in the range 400-1450 °С 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-ZrО₂ → T-ZrО₂ phase transformation was found to proceed completely even when the powders were mechanically mixed in the HTSM process. The М-ZrО₂ phase was identified as traces in the ultrafine 90AZK and 80AZK powder after mechanical mixing, was not found in the 70AZK powder, and emerged as traces in the 58.5AZK powder after 1150 °C. The 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 °С varied topologically continuously without interruption. The dependence of the 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 required 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.