Study On Preparation Of Partially Stable Nano-Zirconia Powder By Co-Precipitation Method

As an excellent inorganic nonmetallic material,zirconia is widely used in the fields of refractories,heat-resistant coatings,teeth,ceramic backplanes for mobile phones,oxygen sensors,wear-resistant cutters and so on,based on its physical and chemical properties such as high melting point,strong slag resistance,high hardness,strong chemical corrosion resistance,low thermal conductivity and good high-temperature ion conductivity.The requirement for the particle size of ceramic powder is getting higher and higher,and the demand for nanometer zirconia is getting stronger and stronger.Therefore,this thesis mainly studies the powder preparation and process optimization of nanometer zirconia,and provides theoretical support for the actual production of nanometer zirconia.The solution of zirconium oxychloride（ZrOCl₂）and magnesium chloride（Mg Cl₂）or yttrium oxide（Y₂O₃）dissolved in hydrochloric acid was used as the main raw material in this thesis.The nano-zirconia powder was prepared by chemical coprecipitation method.The effects of different pH values on the precursor structure of nano-zirconia,the effects of different temperatures on the phase change of yttrium-doped zirconia nano-powders and the effects of different temperatures on the phase change of magnesium-doped zirconia nano-powders were studied.Finally,the optimal sintering temperature and holding time of zirconia nano-ceramics were studied.The influence mechanism of pH value on zirconia precursor was studied,the molecular formula of zirconia precursor with different pH values was determined,the theoretical structure of zirconia precursor with different pH values was put forward,and the crystallization mechanism of nano zirconia influenced by pH values was explained from the molecular level,which provided theoretical support for the production of nano zirconia powder.The phase change of Mg-doped zirconia（8 mol%）nano-powder with increasing temperature was studied.The results demonstrate that the Mg-doped zirconia nano-powder begin to dissolve at 800℃,and the Mg ions completely dissolve at1000℃.The partially stabilized zirconia nano-powder can still be prepared after calcination at 1500℃with the increase of Mg doping amount.The phase change of yttrium-doped zirconia（3 mol%）nano-powder with increasing temperature was studied.The results indicate that some yttrium ions in yttrium-doped zirconia begin to dissolve at 900℃,and a large amount of yttrium ions begin to dissolve at 1400℃.The fully stable yttrium-doped zirconia nano-powder can still be prepared after calcination at 1500℃with the increase of yttrium doping amount.The best sintering process of Yttrium-doped zirconia nano-ceramics is calcinated at 1550℃and held for 3 h.