Preparation And Properties Of Y₂O₃-MgO Nanocomposites

With the acceleration development of the nanocomposite ceramics, a host of new type nanocomposite ceramics spring up. It is made up of functional nano-particles and ceramic matrix, which shows favorable mechanical properties, possesses obvious functionality, and realizes the multifunction of ceramics. Since it possesses superior property of nano-materials and composites, it will be widely applied. In this thesis, fine grain and uniform yttria-magnesium oxide nanocomposite ceramics was prepared by adopting solid phase method and liquid phase method, and using vacuum sintering and pressure sintering.Liquid coprecipitation was adopted in this experiment to get Y2O3-MgO nano composite ceramics. As solubility product of Mg(OH)2 is comparatively large, and its precipitation capacity is weaker than precipitate of yttrium in solution, it is difficult to precipitate Mg2+ and Y3+ together. By changing ratio of the amount of substance between cation and NH3-H2O in the process of reaction, and adjusting NH3·H2O content, it is finally determined that a small amount of Mg(OH)2 can be prepared Under N-drop conditions, if the ratio of the amount of substance between cation and NH3·H2O is 1:10, and a large amount of Mg(OH)2 can be prepared. If the ratio is 1:10, which was prepared by the latter method contains more MgO which is helpful to hinder Y2O3 grains growing too large.Sintering temperature determines the density and grain size of ceramics. This thesis set the atmospheric sintering temperature at 1400℃,1450℃,1500℃, and atmospheric sintering temperature at 1700℃. With the increase of sintering temperature, the density gradually raises. From 1400℃ to 1450℃, the density was improved significantly. With increase of sintering temperature, the grain size got larger. From 1450℃ to 1500℃, the density was improved, and the grain size has a little increase. If the temperature was increased to 1700℃, the grain size grew too large.The grain size of ceramics is about 1.5-1.7μm sintered at the 1700℃ and the micro-hardness is about 850±50HV. With sintering temperature decreasing to 1500℃-1450℃, the grain size decreased to 700-800nm and the micro-hardness increased to 1000HV. With grain size decreasing, the micro-hardness increased. The influence of different content of MgO to hardness is not obvious.Grain size of ceramics that prepared by liquid method is not uniform with a portion of MgO growing in Y2O3.Ceramics prepared by this method is not transparent. Ceramics prepared by the solid phase, with the MgO and Y2O3 volume ratio of 1:1 have uniform grain size. Through this process, MgO and Y2O3 play a role in controlling grain growth with each other and prepared nanocomposite materials. This ceramics have a transmission of 14% in the infrared region.