Preparation And Characterization Of Yttria Stabilized Zirconia Powders

Due to the exceptional properties, such as high thermal expansion coefficient, low thermal conductivity, excellent oxidation resistance and thermal stability, yttria-stabilized zirconia(YSZ) find wide applications in thermal barrier coatings. YSZ nanoparticles material with nono effects presents more excellent properties, such as higher thermal expansion coefficient, more excellent toughness and lower thermal conductivity. Therefore, the preparation of YSZ nanostructured thermal barrier coatings is very valuable, being one of the focus of thermal barrier coatings field. In this paper, YSZ powders were prepared by Solid state synthesis, coprecipitation process and sol-gel method, and the effects of synthesis parameters on the phase stability and morphological characteristic of YSZ powders were discussed. The main conclusions are drawn as the following:(1) YSZ powders were prepared by solid state synthesis. The calcinations temperature, calcinations time and Y2O3 content are of crucial importance for the phase structure of YSZ powders. The tetragonal phase and monoclinic phase coexist in the 9YSZ powders after calcinated at 1400?1600oC for 12?36h, and the content of the monoclinic phase decrease with increasing the temperature and time. Under the same calcinations temperature and time, the content of the monoclinic phase of YSZ powders decrease with the increase of Y2O3 content.(2) The YSZ nanopowders were prepared at low temperature by a coprecipitation process. The results indicate that the tetragonal phase stability is insignificantly affected by p H value and ethanol content in solvent, and the transformation from tetragonal phase to monoclinic phase of the 8YSZ nanopowders prepared with different p H value and ethanol content takes place at 1200 oC. The tetragonal phase stability improves with the increasing of Y2O3 content. For samples 3YSZ, 5YSZ, 7YSZ and 8YSZ, the transformation from tetragonal phase to monoclinic phase takes place at 600, 800, 1000 and 1200oC, respectively. The grain growth trend of YSZ nanopowders is basically the same. The crystallite size increases with the temperature increasing. The crystal growth probably can be divided into two stages that the initial one is before 800oC and the other is beyond 800oC, namely low temperature stage and high temperature stage, respectively. The rate of crystal growth is smaller in the lower temperature stage, while it obviously increases in the higher temperature stage. Due to different growth mechanisms, there is the difference in the activation energy for crystal growth of nanocrystalline YSZ in low temperature stage and high temperature stage. Relatively, the activation energy in low temperature stage is much lower than that in high temperature stage. The activation energy in low temperature stage is insignificantly influenced with the p H value, solvent composition and Y2O3 content, while the activation energy in high temperature stage increases with the increasing of p H value and Y2O3 content, and first decreases and then increases with the ethanol content increasing.(3) With water as solvent and the molar ratio Ac OH/Zr equal to 1:1, the stable tetragonal phase in 8YSZ nanopowders can be prepared by sol-gel process. However, the addition of ethanol in solvent is not beneficial for the stability of tetragonal phase. The crystallite size increases with the heat-treatment temperature increasing. The crystal growth can be divided into two stages, namely low temperature stage and high temperature stage. Relatively, the crystal growth rate in low temperature stage is much lower than that in high temperature stage. The activation energy for crystal growth in low temperature stage is much lower than that in high temperature stage due to different growth mechanisms. The additions of Ac OH and ethanol have different and significant influences on the activation energy for crystal growth. The activation energy in low temperature stage first decreases and then increases with the increasing of Ac OH content, and decreases with the increasing of ethanol content; the activation energy in high temperature stage first increases and then decreases with the increasing of Ac OH content, and first decreases and then increases with the ethanol content increasing.