Marek I. Physico-chemical properties of nanodispersed powders in the ZrO2‒Y2O3‒CeO2 system

Marek I.O. Physico-chemical properties of nanodispersed powders in the ZrO2‒Y2O3‒CeO2 system – Manuscript. The Doctor of Philosophy (PhD) thesis by speciality 02.00.04 – physical chemistry. – Frantsevich Institute for Problems of Materials Sciences NAS of Ukraine, Kyiv, 2021. For the first time, nanodispersed powders of solid solutions based on ZrO2 stabilized by СеО2, Y2O3 and costabilized by these oxides were produced by hydrothermal synthesis in an alkaline medium. Co-precipitated mixtures of hydroxides with a residual moisture content 15–20 wt.% were used. Physicochemical properties (phase and chemical composition, morphology, specific surface area, size of primary particles) of powders have been investigated after preparation and heat treatment in the range 400−1300 °C. The properties of powders were investigated by X-ray phase analysis, differential thermal analysis, scanning electron microscopy, optical microscopy (petrography), low-temperature adsorption/desorption of nitrogen (BET method); chemical and micro-X-ray spectral analysis, modeling of ceramics accelerated aging in hydrothermal conditions. It was found that a ZrO2-based metastable cubic solid solutions (F-ZrO2) crystallized in powders under hydrothermal conditions. The parameters of the F-ZrO2 crystal lattice increased with an increasing of the СеО2 content in the ZrO2 solid solutions. The correlation between the specific surface area of the produced nanodispersed powders and СеО2 content in the ZrO2 solid solutions has not been established. The powders phase transformations under heat treatment have been studied. It was found that the phase transformation F-ZrO2→T-ZrO2 occurs in the range 400−1000 °C, depending on the powders composition. In accordance with the tetragonality degree, it was established that the ability to phase transformation of metastable T-ZrO2→M-ZrO2 increases upon co-stabilization of ZrO2 with yttria and ceria. For the first time the investigation of the structural components evolution of the produced nanocrystalline powders revealed that the primary particles size when heated up to 1150 °C do not change. Peculiarities of changes in the specific surface area of powders are due to phase transformations of ZrO2 and increased sintering activity. The low-temperature phase stability (aging) of ceramics produced from powders that were heat-treated at different temperatures was investigated. The retention of 100% T-ZrO2 in the ceramics of the both compositions (mol.%): 90ZrO2–2Y2O3–8CeO2 and 88ZrO2–2CeO2 was established, which indicates their increased resistance to aging. It was found that the optimum temperature of the initial powders heat treatment was 850 °С. 6. The efficiency of use the obtained powders for ceramic layer coating on a head of a hip joint endoprosthesis by EB-PVD method was carried out. A two-layer coating “metal Zr/ceramic layer” was obtained, in which a columnar microstructure was formed. The fulfilled researches are necessary for microstructural design of composites stable to “aging” in the ZrO2–Y2O3–CeO2 system. Keywords: ZrO2‒Y2O3‒CeO2, hydrothermal synthesis in an alkaline medium, solid solution based on ZrO2, transformation hardening, metastable phases, aging.