PHYSICO-CHEMICAL POWDER PROPERTIES IN THE Al2O3-ZrO2-Y2O3-CeO2 SYSTEM, OBTAINED BY COMBINED METHOD

Abstract

The Al2O3 – ZrO2 (Y2O3, CeO2) system is promising for creation the composites for various purposes: structural, functional and medical. ZTA – zirconia toughened alumina belongs to the transformation-reinforced composites. The complex doping of ZrO2 with Y2O3 and CeO2 does not only increase the strength characteristics, but also increases the ageing resistance of ZrO2- based composites. ZTA - nanopowders containing 20-30% (wt.) ZrO2 (Y2O3, CeO2), were obtained by a combined method: hydrothermal synthesis in alkaline medium with following mechanical mixing. The properties of ZTA - nanopowders are determined by synergetic effect of all components. Phase transformations of Al2O3 and ZrO2 - based solid solution (cubic F - ZrO2 → tetragonal Т - ZrO2 → monoclinic М - ZrO2) took place during thermal treatment. Nanocrystalline powder of ZrO2 (Y2O3, CeO2) solid solution was hydrothermally synthesized in an alkaline medium. A metastable low-temperature F - ZrO2 was formed. To prevent the influences of phase transformation of Al2O3 and ZrO2, it is advisable to use the α- Al2O3 as initial powder. Mixing of ZrO2 - based solid solution powder with α- Al2O3 was carried out in a ball mill. To study the regularities of change in physical and chemical properties, the powders were thermal treated in the temperature range 400-1450 °C with a 2-hour exposure at each temperature. Methods of investigation - X-ray diffraction (XRD) and differential-thermal analysis (DTA), BET method and scanning electron microscopy (SEM). A series of endo-effects were noted on DTA curves in this temperature range, which correspond to the minimum on the DTG curves. Endothermic effects on the DTA curves are associated with the residual moisture. The following effects may correspond both to processes of ZrO2 - based solid solution transformations from an amorphous to crystalline state and to the aggregation of particles, and to the ZrO2 - based solid solution phase transformations. According to the XRD, the F - ZrO2→ Т - ZrO2 phase transformation was completed at 1000°C. During the thermal treatment up to 1000 °C, М- ZrO2 was not formed. The morphology of the powders changes topologically continuously.

Keywords

• ZTA
• комбінований метод
• Al2O3
• гідротермальний синтез
• система Al2O3–ZrO2–Y2O3–CeO2