Process Optimization And Growth Mechanism Of Aluminum Nitride By Combustion Synthesis

AlN is a kind of promising ceramic material with excellent electrical,mechnical and thermal properties with wide application prospect.In recent years,it has attracted lot of researching interests.AlN powders or whiskers is important for its subsequent application.AlN can be prepared by various method.However,pure AlN whiskers with fine particle size distribution and morphology is hard to obtatin.In present research,AlN whiskers were fabricated under high nitrogen pressure by using self-propagation high temperature systhesis method.In order to obtain pure AlN whiskers,the influence of nitrogen pressure,Al:AlN ratio and rare earth oxide content on AlN whisker phase and morphology were studied.The main results are as following.The influence of diluent were studied.AlN powers were used as the diluent in this research.AlN is inert during the combustion synthesis process and had siganificant impact on the final morphology of as prepared AlN powders and whiskers.The results showed that the AlN whiskers content of as-prepared samples reached the maximum when Al and AlN mass ratio was 3:2.When the Al and AlN mass ratio was1:3,the residual Al in the final sample was the highest.Nitrogen pressure is a major factor on the properties of final AlN powders.In the present experiment range of nitrogen pressure,higher nitrogen pressure was helpful to reduce the residue of aluminum.Compared with synthesing other nitrogen compounds,such as Si₃N₄,the combustion of aluminum is more intense,and the activation energy required for reaction is lower.Therefore,the consumption of nitrogen was faster in AlN combustin synthesis.The optimum range of nitrogen pressure is higher than that reported for synthesizing other nitrogen compounds.Y₂O₃ and La₂O₃ were chosen additives.The Al content in as-prepared samples were lowest when gallium oxide content doped between 2wt%-4wt%.The most pure AlN whiskers were fabricated when gallium oxide and yttrium oxide mass ratio was1:1.The results of microstructure of AlN whiskers in this research showed that AlN whisker were grown via mainly through VS mechanism when no oxide additive added.With rare earth oxide add,AlN whiskers were grown via VS and VLS hybrid growth mechanism.