Smyrnova-Zamkova M.Yu. Effect of production methods on physicochemical properties of nanocrystalline powders in the Al2O3-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, nanocrystalline and ultrafine powders based on Al2O3 with a high content of ZrO2 were produced by hydrothermal synthesis in alkaline medium (HTS) and by the combined method of hydrothermal synthesis/mechanical mixing (HTSM). The physicochemical properties of powders (phase and chemical composition, specific surface area, size of primary particles, morphology, form factor) were investigated after thermal treatment in the temperature range 400–1450 °C.
The powders properties were studied by X-ray phase analysis (XRD) (DRON-3M powder diffractometer (Cu-Kα-radiation , Ni-filter), the scan rate varied from 1 to 4 deg/min.), differential thermal analysis (DTA) (derivatograph Q-1500 D, heating rate in the temperature range 20–1000 °C was 10 °C/min), scanning electron microscopy (scanning electron microscope with energy micro analyzer REM 106Y) (the carbon film was sprayed on the powder samples). The powders specific surface area was determined by the method of thermal adsorption-desorption of nitrogen (BET). The crystallite size were calculated by Scherer formula. The AMIС program ("Automatic Microstructure Analyzer") was used for the data processing of the powders morphology.
It was determined that metastable F-ZrO2 as well as boehmite were formed in the powders after HTS. With increasing the ZrO2 content, the temperature of phase transformation F-ZrO2→T-ZrO2 decreases in 150 °C and the probability of M-ZrO2 formation increases. With HTSM, the phase transformation F-ZrО2→T-ZrО2 takes place completely during the mechanical mixing. According to temperature dependences of the size of primary particles and specific surface area of the powders, the high activity of the produced powders to sintering was found.
It was established that under heat treatment form factors of the powders obtained by both methods vary similarly to form factors of the initial blends. The powder “soft” agglomerates with a form factor of 0.9, which corresponds to polyhedral agglomerates of the regular shape, were formed.
The distribution of agglomerates by form factor depends on the physicochemical processes that take place in the powders during heat treatment. This confirms that with the same phase composition, the powder morphological features are determined by the production technology. The effect of "topochemical memory" during the powders heat treatment was shown.
The produced powders are promising for the designing of high-tech ZTAcomposites of the Al2O3–ZrO2–Y2O3–CeO2 system, in which particles of the solid solution based on ZrO2, costabilized by CeO2 and Y2O3, are dispersed in the Al2O3 rigid matrix.
Keywords: Al2O3–ZrO2–Y2O3–CeO2, ZTA-composites, hydrothermal synthesis in the alkaline medium, mechanical mixing, form factor, ZrO2-based solid solution
