Fabrication And Optical Property Optimization Of ZnO Transparent Ceramics

The research development of transparent ceramic has been extended from cubic crystal structure materials to low symmetry crystal material system,while the research on the fabrication and optical transmittance optimized of low symmetry crystal structure materials are emphasis and difficulties.A problem influence ZnO transparent ceramic applicated in scintillation detection is that ZnO was the hexagonal symmetry of its crystal structure makes it low transparency.Hence,preparation of polycrystalline ZnO nanosized powder and ZnO transparent ceramic were systematically studied in this dissertation.Grain size and orientation factor influence on in-line optical transmittance model depend on ZnO transparent ceramic has been established based on Rayleigh–Gans–Debye theory.ZnO transparent ceramics which meet the microstructure requirements of the model were effectively controlled by slip casting process under a strong magnetic field and designing SPS sintering parameters.Base on these data,we find that the calculation results of theoretical model match well with the experiment results.The specific results are as follows:ZnO precursor was prepared by homogeneous precipitation using Zn（NO₃）₂·6H₂O as raw material and urea as precipitant.And ZnO nano-sized powders with adjustable particle size were obtained by calcinated at different temperatures.The factors of raw material concentration,precipitant concentration and reaction time influenced the yield and morphology of ZnO nanoparticles were investigated by the orthogonal experimental method.Experimental results show that precipitant concentration was the main factor affecting yield and grain size.The optimized process parameter was that concentration of urea was 0.45 mol/L,the concentration of zinc nitrate was 0.2 mol/L,and the reaction time was 6 h.The particle size increases with the increase of calcining temperature,grain size of obtained ZnO powder increased successively from 35.8 nm to 200 nm,specific surface area decreases from 28.1 m²/g to 16.9 m²/g as the calcination temperature increased from 400℃ to 700℃.Meanwhile,the particle size distribution tends to be uniform.The sintering behavior of ZnO ceramics without pressure at air,oxygen,vacuum three different sintering atmosphere was studied.And using monodisperse ZnO powder with particle size of about 120 nm prepared by precipitation as raw powder.ZnO ceramic sintered in air sintering atmosphere with the highest relative density was 98.1%,sintering temperature was 1300℃,with mean grain size of 70μm.ZnO ceramic sintered in oxygen sintering atmosphere shows the highest sintering temperature（1500℃）with mean grain size of 80μm,but relative density only 97%.ZnO ceramic sintered in vacuum with relative density of 98.4%and mean grain size of 14.7μm shows the best in-line optical transmission of 1.6%at the wavelength of 600 nm compared with other pressure-less sintering processes.Pressure-less sintering result ZnO ceramic not dense to make ceramic transparent.ZnO transparent ceramics prepared by SPS with mean grain size of 0.66μm was obtained by sintering at 850℃ for 10 min under 80 MPa leading to good optical transmission of 12.9%at the wavelength of 600 nm.A light scatting influence on in-line optical transmittance model has been established for the birefringence of ZnO transparent ceramic based on Rayleigh-Gans-Debye approximation scattering theory.It is proposed that grain size and grain orientation in ZnO ceramics are two important parameters affecting optical transmittance under the condition of sufficient density.The distribution of grain orientation in ZnO ceramics was obtained by XRD,combined with the relation between XRD and orientation factor,the effects of grain size and texture of ZnO ceramics on linear optical transmittance were simulated.In order to obtain ZnO transparent ceramics with good optical transmittance,the texture of ZnO transparent ceramics should be improved as much as possible on the basis of decreasing grain size.ZnO transparent ceramics with smaller grain size were obtained by raise the temperature of applied pressure during the process of SPS.Microstructure of ZnO transparent ceramics were effectively controlled by designing SPS sintering parameters and slip casting process under a strong magnetic field.Corresponding results show that the in-line optical transmittance of non-textured ZnO transparent ceramic increased from 12.9%to 21.6%at 600 nm as grain size decrease from 0.66μm to 0.35μm while that of textured ZnO transparent ceramic（mean grain size 0.35μm）was improved greatly from 21.6%to 36.6%at 600 nm due to the increasing of the orientation factor to 24.7%calculated from XRD data.Based on these data,we find that the calculation results of theoretical model match well with the experiment results.This paper has proved that fine grain size and orientation can improve the in-line optical transmittance of ZnO transparent ceramic in theory and experiment.This research method provides theoretical model and experimental basis for the study of excellent optical transmittance ZnO transparent ceramics.