Investigation On Synthesis And Defects Of Nano-ZrO₂

Zirconia is a technologically important material due to its thermal and chemical stabilily, and excellent mechanical properties, such as high strength,high melting point , Low thermal conductivity , and high corrosion resistance.These unique mechanieal and electronic properties of ZrO₂ ceramics have led to their widespread applications in the fields of structural materials , thermal barrier coatings ,oxygen-sensor,fuel cell,catalyst and catalytic support,a possible high dielectric contant material for very large scale integrated circuits,and as a gate dielectric in metal oxide-semiconductor dvices. The density ceramic with good microstructure can be obtained at lower temperature using ultrafine powders with a narrow size distribution,and it may have good properties.In this paper, ZrO₂ powder prepared using ZrOCl₂ and Y(NO₃)₃ as raw materials and NH₃·H₂O as the precipitant with sol - gel method, pressure - hydrothermal method and supercritical fluid drying (SCFD) in order to prepare from well dispersed, and the prominent anti-aging properties of the nano-ZrO₂ powder for the purpose. The effects of the initial zirconium concentration, adding ammonia method and speed of precipitant, the PH value of the solution, and aging time on the ZrO₂ powder agglomeration state, phase composition, particle size and powder morphology were investigated in this paper. Nano-ZrO₂ powder phase composition and grain size for quantitative analysis and DTA, XRD and TEM methods such as testing the performance of heat-treated powder have been characterized.The results show that,zirconium oxide powder prepared with using sol-gel and pressure-hydrothermal method was amorphous phrase, the crystallization temperature is about 500℃;And as pressure increases, powder crystallized degree gradually raised, powder crystallized basically when the pressure reached critical pressure; It is found that doped Y₂O₃ can make the high temperature stability phase of zirconium oxide(t - ZrO₂) Exists in room temperature,and with increasing Y₂O₃ content , tetragonal phase content increase and grain size change, the average grain size reaching the minimum of 6nm when doping 3.0mol﹪Y₂O₃ ,and tetragonal phase content reach 80﹪;With the increase of the heat treatment temperature and the extension of time, average grain size of ZrO₂ powder is gradually increasing, and powder transition from t-phase to m-phase gradually; the powder doesn't include t-ZrO₂ fundamentally when the temperature reaches to 950℃,and microscopic strain decreased with the extension of heat treatment time and with the rise of temperature, when the temperature reaches 950℃, the microscopic strain of the powder close to zero;Nano-ZrO₂ powder made by SCFD method was almost t-ZrO₂, the average grain size was no more than 10nm, and they separated spontaneously.After 6 hours of heat treatment on 500℃, the crystalline grain grown less than 5nm, and microscopic strain decreased with the extension of heat treatment time.