Study On The Nitriding Reaction Of Aluminum-alumina Mixed Powder

In III/V nitrides,aluminum nitride(AlN)is considered to be a modern and new functional ceramic material widely used in electronics,optics,ceramics and matrix materials.Commercial AlN powders are mainly industrially synthesized by two methods,namely,direct nitridation and carbothermal reduction.However,the aluminum nitride obtained by the direct nitridation method is easily agglomerated into a block shape;the alumina carbon thermal reduction method requires a high temperature and a long reaction time.Based on two traditional methods for industrial production of aluminum nitride powder,under the condition of micro-positive pressure,this paper systematically explores the difference between alumina-aluminum powder nitridation reaction and aluminum-alumina carbothermal reduction nitridation reaction.Attempts have been made to combine direct nitridation and carbothermal reduction to achieve the goal of improving the agglomeration of the aluminum nitride product,lowering the reaction temperature,and shortening the reaction time.The nitridation reaction was carried out under conditions of a slight positive pressure and a nitrogen flow rate of 1.5 L/min.Aluminum powder,alumina powder and graphite powder were used as raw materials to change the ratio of raw materials,holding time and reaction temperature to explore the influence on the phase and microscopic morphology of the nitrided product.The experimental results show that the addition of aluminum powder is beneficial to increase the activity of alumina.The aluminum-alumina mixed powder is introduced into nitrogen at 1500 °C for more than 30 min,and is completely converted into AlON and AlN.As the proportion of alumina in the mixed powder increases,the phenomenon of sintering agglomeration which occurs in the direct nitriding process of the aluminum powder is alleviated.The addition of graphite powder to the aluminum-alumina mixed powder significantly promotes the nitridation reaction of the alumina and improves the dispersibility of the aluminum nitride product.The mixed powder of graphite,alumina and aluminum with a mass ratio of 1:1:4 can completely form aluminum nitride with good dispersibility when the reaction temperature is 1500 ° C and the reaction time reaches 90 min.An example of an optimized process scheme is obtained by combining two industrialization methods: graphite,alumina and aluminum powder are mixed according to a mass ratio of 1:1:4,at reaction temperature of 1500 ° C,holding time of 120 min,micro-positive pressure.Pure aluminum nitride powder was obtained under a nitrogen flow rate of 1.5 L/min.The reaction temperature and reaction time are lower than the alumina carbothermal reduction method,and the dispersibility of the aluminum nitride product is superior to the direct nitriding method of the aluminum powder.