Study On Preparation And Properties Of High Purity AlON Powders

AlON transparent ceramics were widely used in military and commercial fields due to excellent performances,and it was considered as a kind of potential infrared materials,which can be applied to the infrared window,fairing and other components.The preparation of AlON transparent ceramics could not be separated from AlON powders with excellent properties.Therefore,it is of great significance to study the preparation of AlON powders.In this paper,AlON powders were synthesized by carbothermal reduction and nitriding process withγ-Al₂O₃ and carbon black as raw materials.The effects of ball milling time,mixture ratio of raw materials,heat preservation time,reaction temperature and heating rate on the synthesis of AlON powder were studied.The results shows that prolonging the ball milling time can reduce the particle size of the mixedγ-Al₂O₃/C powders,increase the uniformity of the mixture of raw materials,and be beneficial to the synthesis of single phase AlON powder.The ratio of raw materials has little influence on the morphology and particle size distribution of the powder,but it will affect the phase composition of the synthesized powders.The composition of synthesized powder was single-phase AlON when the content of carbon powder ranges from 5.6-6.0wt%.The heat preservation time is one of the factors that affect the phase composition of AlON powders.With the decreasing of the holding time,the particle size decreased gradually and the best heat preservation time was 1h.The composition of synthesized powder was single-phase AlON when the synthesis temperature ranged from1700-1800℃.With the decreased of the synthetic temperature,the particle agglomeration phenomenon was obviously weakened and the best synthesis temperature was 1700℃.At the high temperature part of the synthetic powders（1000℃）,when the heating rate was 20℃/min,in addition to AlON powders,Al₂O₃ powders remained in the product.It was single-phase AlON that could be prepared as the heating rate was 10℃/min and the particle size of the powders was small,and the best heating rate was 10℃/min.Comprehensive analysis,the best synthesis system for obtaining high purity AlON powder is as follow.The raw material was ball milled for 12h with the carbon content was 5.8wt%,then it was calcined at 1700 ℃ with the heating rate of 10 ℃/min.Because the temperature of the synthesized AlON powders was up to 1700℃,some agglomeration phenomena could not be avoided in the powder.The powders with larger particles were not conducive to the preparation of high quality AlON transparent ceramics,which required the post treatment of the synthesized powders.In this paper,the synthesized AlON powders were treated by three post-processing methods,ultrasonic dispersion,freeze-drying and ball milling.Research shows that the ultrasonic dispersion and freeze drying of the two kinds of post-processing methods had little effect on the size and morphology of AlON powders,but ball milling had great influence on the AlON powders.When the milling time was 12h,AlON powders with fine grain size,uniform grain size and regular morphology could be obtained.Finally,the AlON transparent ceramics were prepared by adding a certain amount of sintering aids to the treated AlON powders,and the effect of the sintering time on the AlON transparent ceramics was preliminarily discussed.When the holding time was 24h,the density of the ceramics was low,and the ceramic density would be increased if the holding time was properly reduced.