Study On The Preparation Of Aluminum Oxynitride Powder Material For Transparent Ceramics

Aluminum oxynitride（AlON）transparent ceramics have hardness comparable to sapphire,high optical transmittance and excellent physical and chemical properties,and have very important applications in military transparent ceramic armor,infrared wave-transparent windows,etc.AlON transparent ceramics are regarded as one of the most important defense materials in the 21st century.In this thesis,composite powders of alumina precursor particles and activated carbon powder particles were prepared by homogeneous precipitation method,and high performance AlON ceramic powders were prepared by high temperature carbon thermal reduction.Systematic investigation and product characterization were carried out,and monodisperse spherical Al₂O₃and pure phase AlON ceramic powders were successfully prepared.（1）Al₂O₃ precursor powder was prepared by chemical precipitation method,and monodispersed spherical Al₂O₃precursors were obtained by improved chemical precipitation process.Monodispersed spherical alumina precursors were prepared by homogeneous precipitation method.The effects of holding time,the ratio of ammonium sulfate to aluminum nitrate（R）,the ratio of urea to aluminum nitrate（K）,and the overall concentration of the system on the homogeneous precursor alumina precursors by homogeneous precipitation were investigated during the homogeneous precipitation preparation.The obtained spherical alumina precursors were calcined and Al₂O₃transparent ceramics were prepared by discharge plasma sintering.The results showed that during the homogeneous precipitation,the particle size of powder increased with the extension of holding time.Ammonium sulfate addition made the aluminum nitrate solution precipitate successfully,and the alumina particles had the best sphericity and dispersion performance when the ratio of ammonium sulfate to nitric acid was 0.7.When the ratio of urea to aluminum nitrate was 10～15,the dispersibility of the product is the best,and with the increase of the ratio,the particle size of the powder changes little,and the dispersibility becomes worse.When the concentration of the solution system increases,the agglomeration of powder is serious and the particle size is uneven.The best preparation process of monodisperse spherical alumina was as follows:Al³⁺=0.006 mol/L,R=0.7,K=15 homogeneous precipitation for 2 h.The alumina precursor was transformed into sphericalα-Al₂O₃after calcination at 1200℃,and the highest transmittance in IR band was57.4%after SPS sintering.（2）On the basis of homogeneous precipitation of monodisperse spherical alumina powder,a composite powder of activated carbon powder and spherical alumina precursor was prepared,and high purity AlON powder was obtained after calcination at high temperature and nitrogen atmosphere.The effects of activated carbon powder content,homogeneous precipitation system concentration,calcination temperature and powder loading on the composition of AlON phase were investigated.The study shows that the addition of activated carbon powder can reduce the particle size of spherical alumina precursors.When the addition of activated carbon powder is 6.8 wt%,the pure phase AlON powder can be obtained by calcination at 1750℃.After increasing the concentration of the system,the calcined powder contains a large amount of Al₂O₃and Al N impurities.The decarbonization can remove the residual carbon and graphite in the powder.The best preparation process for AlON powder is:homogeneous precipitation composite powder（6.8 wt%active carbon powder content）,calcination at 1750℃under nitrogen atmosphere for 1 h,decarburization at 750℃under air atmosphere.（3）The dense AlON ceramics were prepared by sintering using the developed pure AlON ceramic powder.The pure phase AlON ceramics were successfully prepared by discharge plasma sintering（SPS）.The effects of sintering temperature and pressure on AlON ceramics were initially discussed.The densities of AlON powders were 89.67,94.71,and 95.1%after sintering at 1400,1450,and 1500℃for 10 min,respectively,and the hardnesses were 13.7,17.06,and 17.93 GPa,respectively.The relative density and hardness of AlON ceramics decreased to 93.2%and 15.6 GPa,respectively,after sintering at 1500℃and reducing the pressure to 30 MPa.