INFLUENCE OF THERMAL TREATMENT ON THE PHYSICAL AND CHEMICAL PROPERTIES OF NANOCRYSTALLINE 88 ZrO2 - 12 CeO2 (MOLE %) POWDER

Transformation toughening, based on the martensitic T-ZrO2 → M-ZrO2 phase transformation, causes the high strength of ZrO2-based composites. The reversible martensitic phase transformation of fine-grained composites ZrO2–12 mol% CeO2 occurs below ambient temperature. Bulk material 12Се-TZP is characterized by “shape memory”, high fracture toughness (К1с up to 35 МПа·м 0,5) and tolerance to aging. Properties of composites depend on the properties of the starting powders. Hydrothermal synthesis in an alkaline medium is perspective for producing nanocrystalline powders of ZrO2-based solid solutions . Variations of physico-chemical properties of hydrothermal nanocrystalline 88 ZrO2–12CeO2 (mol%) powder after synthesis and thermal treatment in the 400–1300 °C range were investigated. It was found that after hydrothermal synthesis the thermodynamically non-equilibrium system consisting of a low temperature metastable cubic solid solution based on ZrO2 (F-ZrO2) and an X-ray amorphous phase were formed. The primary particles size was ≈ 10 nm. The powder specific surface area was 107 m2/g. Low-temperature F-ZrO2 remained up to 700 °C. Temperature increase up to 850 °C was accompanied by the F-ZrO2→T-ZrO2 phase transformation. This transformation is completed at 1000 °C. The powder specific surface area decreases from 107 m2/g to 0.27 m2/g during thermal treatment. Variation of powder specific surface area depends on both the ZrO2- based solid solution phase transformations and the sintering of freely poured powders. The primary particles size of the ZrO2-based solid solution increased to 20 nm. Morphology of powder varies topologically continuously during thermal treatment. The unit cell volume of T-ZrO2 phase decreased from 135.32 to 135.20 A after thermal treatment in the 1150–1300 °C range. Under these conditions the T-ZrO2 tetragonality increases from 1.0137 to 1.0139. Powder was characterized by high activity to sinter ing. The investigation results will be used for microstructural design of high-performance ZrO2-based composites