Using zirconium oxychloride as raw material, urea as a mineralizer, yttrium oxide as a stabilizer, and water and ethanol as the reaction solvent, combined with a one-step hydrothermal method, the formation mechanism of spherical tetragonal zirconia was investigated by changing the hydrothermal temperature, hydrothermal time, alcohol-water ratio and the amount of yttrium oxide without adding surfactants or calcination. Tetragonal zirconia powders with good crystallinity, uniform particle size distribution, and high sphericity were prepared.

As advanced ceramic materials, Si₃N₄ ceramics are widely used in strong thermal shock environment in aerospace field because of the excellent properties such as high temperature resistance and corrosion resistance. The Si₃N₄ composites prepared by hot pressing sintering had high flexural strength, but the thermal shock resistance decreased rapidly with the increase of temperature. The hot pressing sintering process was still insufficient to enhance the thermal shock resistance. In this paper, a secondary heat treatment method of hot pressing sintering-gas pressure sintering was proposed to improve the thermal shock resistance of Si₃N₄ ceramics, and obtain a denser Si₃N₄ ceramic material with better thermal shock resistance. The results showed that with the increase of thermal shock temperature and times, the probability of micro-cracks in the Si₃N₄ ceramics prepared by conventional hot pressing increased, and the bending strength of the samples decreased gradually after thermal shock, with the average strength reduction rate reaching 23.48% at 1200℃. After the second heat treatment, the flexural strength of Si₃N₄ ceramics samples decreased slightly, but the thermal shock resistance was obviously improved. With the increase of heat treatment time, the microstructure of Si₃N₄ ceramics after the second heat treatment became denser, and the thermal shock resistance was obviously improved. The strength reduction rate of the sample decreased significantly after 10 times of thermal shock at 1200℃, which was about 12.31%. Method of improving the thermal shock resistance of Si₃N₄ ceramics was proposed to study the thermal shock resistance and the attenuation law of Si₃N₄ ceramics at 1200℃, which provided a reference for improving the high temperature performance of silicon nitride ceramic devices.