Preparation Of ZrO₂ Coated Y₂O₃ Nanometer Powders And Preparation Of Transparent Ceramics By Colloidal Forming Process

Y2O3 has good physical and chemical properties,such as high thermal conductivity and high dielectric constant.In addition,Y2O3 also has the advantages of low phonon energy,large conduction band gap to valence band that can accommodate most of the emission level of trivalent rare earth ions,and so on.These characteristics make Y2O3 transparent ceramics have important applications in high temperature window,infrared detection and other fields,such as infrared missile window and fairing.However,in the process of developing transparent ceramics,the forming process can easily lead to defects,and it is difficult to make up through subsequent processes.Therefore,it is extremely important to perfect the forming process for the preparation of transparent ceramic materials.At present,shaping way of transparent ceramics has dry pressing molding,plastic molding and colloidal forming.However,dry pressing and plastic forming ceramics have a single shape and generate internal stress,and colloidal molding can not only form ceramics of various shapes,but also produce transparent ceramics with uniform microstructure,which is more conducive to obtaining its high optical transmittance.Therefore,this project will adopt the method of colloidal forming to prepare yttrium oxide transparent ceramics.However,Y2O3 powder is easily hydrolyzed in aqueous solution,which seriously affects the dispersion stability of Y2O3 suspension and the preparation of transparent ceramics.Therefore,in this study,ZrO2 was used to coat Y2O3 powder by surface modification.In addition,in the sintering process of Y2O3 transparent ceramics,ZrO2 can also be used as a sintering assistant to obtain transparent ceramics with high optical transmittance.In this study,four different coating methods were used to coat Y2O3 powder,and the water resistance and dispersion of coated Y2O3 powder and the fluidity and stability of prepared Y2O3 suspension were studied.By analyzing the changes of pH value and settlement height of Y2O3 suspension with time,it is found that Y2O3 suspension obtained by ball-milling Y2O3 powder mixed with zirconium nitrate for 24 h has good stability and fluidity.After calcination at 900℃,the coated Y2O3 powder obtained has uniform particle distribution and fine size.Through sintering behavior analysis,it was found that yttrium oxide transparent ceramics with high density and high optical transmittance could be obtained by presintering of the Y2O3 blank at 900℃.Then,the influence of adding amount of ammonium citrate(TAC),ball grinding time of yttrium oxide suspension and solid phase volume fraction of Y2O3 suspension on the preparation of Y2O3 transparent ceramics by centrifugal casting molding was systematically studied.The results show that yttrium oxide suspension has good stability and fluidity when the additive amount of dispersant is 1.5 wt%of the mass of Y2O3 powder.When the ball grinding time is 8 h,the density of the Y2O3 blank is the highest,the optical transmittance of the 1.0 mm thick Y2O3 transparent ceramics prepared by vacuum sintering at the wavelength of 800 nm is 78.4%.In order to improve the transmittance,a transparent ceramic with a solid volume fraction of 35 vol%was developed,the yttrium oxide blank density reached 2.55 g/cm3,and the optical transmittance of 1.0 mm thick Y2O3 transparent ceramics at 800 nm reached 81.3%after vacuum sintering.Finally,the influence of centrifugal gel injection molding and Isobam gel injection molding on the preparation of Y2O3 transparent ceramics was investigated.When using centrifugal gel injection molding,through the analysis of Y2O3 blank density along with the change of centrifugal speed and time,found that when the centrifugal speed of 4000 r/min for 40 min,the centrifugal time Y2O3 blank for highest density,uniform ceramic microstructure after sintering,the resulting 1.0 mm thick the optical transmittance of Y2O3 transparent ceramics at 800 nm as high as 76.4%.When using Isobam gel injection molding,TAC system is studied with Isobam amount and Y2O3 suspension of solid phase volume fraction on the influence of the preparation of Y2O3 transparent ceramics.It was found that when TAC and Isobam were 0.30 wt%and 0.15 wt%of the mass fraction of Y2O3 powder and the solid volume fraction of Y2O3 suspension was 25 vol%,respectively,Y2O3 blank density is highest,and the transparent ceramics of 1.0 mm thick have the high optical transmittance of 73.7%at 800 nm.