| Aluminum oxynitride(γ-AlON)ceramics with a spinel structure is a singlephase solid solution in the Al2O3-AlN binary system,which possess excellent light transmission in the wavelength range of 0.2 μm to 6 μm.At the same time,it has the advantages of high mechanical strength and chemical corrosion resistance,and has important applications in military and civilian high-tech fields.Surmet Corporation of the United States is currently the world’s best AlON transparent ceramic research and manufacturing unit.It has realized the commercialization of AION transparent ceramics for infrared domes and windows,with a maximum size of 18*35 inches.However,related research in china started late,and there is still a big gap from the world’s advanced level.At present,there is no commercial powder,and the sintering process is immature,moreover the knowledge of materials is not sufficient.These fartors all limit the development of domestic AlON transparent ceramics.In response to these problems,this paper studies the preparation of AlON powder by high-temperature solid-state method and carbon thermal reduction combustion precursor.Then we studies the densification process of the prepared powder and the microstructure and properties of as prepared ceramics,and prepares a high-strength and high-transmittance AlON powder.AlON ceramics.The main research work is as follows:(1)Preparation of AlON powders by high-temperature solid-state method and its sintering densificationUsing alumina(γ-Al2O3)and aluminum nitride(AlN)powder as raw materials,AlON powder was prepared by high-temperature solid-state reaction method,and the influence of raw material ratio and synthesis process on the properties of AlON powder was studied.The AION powder with an average particle size of 1.2-1.6 μm,specific surface area of 5.2-6.8 m2/g and metal impurity content less than 0.01 wt.%was prepared by reacting at 1700 ℃ for 1 h at a ratio of γ-Al2O3 of 73 mol%and AIN of 27 mol%.The granulated powder with bulk density and tap density of 1.20 g/cm3 and 1.49 g/cm3 was prepared by spray granulation technology,which has good formability and fluidity(under the pressure of 200 MPa,the green density was as high as 2.51 g/cm3).The green body sintering densification and microstructure and performance regulation technology were studied.AlON ceramics with a relative density of 99.90%,a grain size of 189 μm,a flexural strength and a hardness of 275 MPa and 16.5 GPa were prepared after sintering at 1900℃ for 20 h.The light transmittance at 2μm wavelength reached 84.3%.(2)Preparation of ultrafine AION ceramic powders by carbothermal reduction solution combustion precursorThe method of preparing AlON ceramic powder by carbothermal reduction solution combustion precursor was studied.Using soluble aluminum salt,organic carbon source glucose and urea(fuel)as raw materials,highly active alumina and carbon(Al2O3+C)were prepared by solution combustion method,the AlON ceramic powder can be obtained through carbothermal reduction.The types of aluminum salts such as aluminum nitrate(Al(NO3)3),aluminum chloride(AlCl3),aluminum sulfate(Al2(SO4)3)and the ratio of aluminum source to carbon source,synthesis temperature and holding time were studied in detail.The precursors prepared with Al(NO3)3 as the aluminum source were found to have a bilayer lamellar structure,and the specific surface area of the precursors was as high as 27.65 m2/g with high reactivity.When the carbon content of precursor was 5.24 wt.%,the pure phase AION powder can be obtained,after 10 min of reaction at 1700℃,the D50 of powder was 0.56 μm,and the specific surface area was as high as 29.77 m2/g.(3)Preparation of high-strength and high-transparency AION ceramicsAION ceramics were prepared from ultra-fine AION powder synthesized by carbothermal reduction combustion precursor,and the two-step sintering densification process of the powder and the relationship between the microstructure and mechanical properties of the material have been studied.Due to the large specific surface area and high sintering activity of the prepared powder,after sintering at 1 700℃ for 3 h,the density of the material was as high as 97.34%,the average grain size was only 2.53 μm,and the flexural strength was as high as 526.9 MPa.Using the characteristics of high sintering activity of ultrafine powder,high densities were first obtained by grain boundary diffusion at low temperature,and then warmed up to 1850℃ for 3 h.AION ceramics with 99.91%density,61.2 μm average grain size,375.1 MPa flexural strength,and 85.4%transmittance at 2 μm wavelength could be prepared. |
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