Preparation And Characterization Of Spinel AlON Transparent Ceramics

The spinel aluminum oxynitride(AlON) is an important single-phase,stable solid solution ceramic of Al₂O₃-AlN system,and has become a quite potential new material with unique performances.There are some excellent optical,physical,mechanical and chemical properties of AlON ceramics,in particular which can be sintered into the transparent one for its isotropy,and it is the optimum material for the infrared windows and covers to resist high temperature.In the dissertation the high-purity AlON micropowder was synthesized first,then the transparent AlON ceramics were prepared from AlON micropowder and Al₂O₃,AlN,Al powders respectively;at last,the properties and structures were analyzed and characterized.In the first part of the dissertation,high-purity AlON ceramics were prepared in the technology of pressureless sintering under nitrogen-based atmosphere with raw materials of Al₂O₃,AlN powders and Al₂O₃ sol,AlN powder separately.The compositions of the phase were determined by XRD,the fracture appearance was analyzed by SEM.The results indicate:in the experiment,the aluminum oxynitride phase in the AlON ceramics existed in the form of Al₅O₆N, whose solid-solution zone is 33.4 mol%AlN belonging to spinel strctures.The grain size of high-purity AlON is smaller with average size 3μm.The spinel AlON transparent ceramics,which were prepared with raw materials of AlON micropowder and Al₂O₃,AlN,Al powders separately,and with sintering aids of Y₂O₃ and MgO,were investigated in the second part of the dissertation.The mixtures were isostatically pressed under 150MPa,then sintered by pressureless sintering under nitrogen-based atmosphere. The temperature was preserved 3h at 1900℃.The grains of the transparent AlON ceramics (2mm) grow perfectly and distribute uniformly.The grain boundary is smooth without other phases.The greatest transmittance in the ultraviolet-visible region is 70%,the density and the three point bending strength are 3.70 g/cm³ and 201MPa,respectively.The results show that the higher purity of the AlON micropowder,the higher sintering temperature,and the bigger forming pressure can obviously promote the transmittance.When sintered,the grains will grow abnormal if the holding time is too long,which is harmful to the mechanical strength of the ceramics,and for the tansmittance,the hot pressing sintering is more benefical than the pressless sintering under nitrogen atmosphere.It is proved the high-purity AlON powder as materials is better to the transmittance than that of the Al₂O₃,AlN,Al powders.