Green Synthesis And Characterization Of Aluminum Nitride Superfine Powder

In modern society, science and technology has been developed rapidly, so the properties of materials are required to be more excellent. Aluminum nitride has a series of unique properties, such as nontoxic, high thermal conductivity, high electrical resistivity, low dielectric loss and dielectric constant and thermal expansion coefficient close to that of silicon. These characteristics make aluminum nitride ceramic to be the ideal substrate material for electronic equipment, especially in large power integrated circuit. The preparation of aluminum nitride powder with high purity, small size and uniform distribution is the key to obtain aluminum nitride ceramics with outstanding properties.In this paper, precipitation method is used to prepare alumina powder using anhydrous sodium carbonate and hydrated aluminium chloride as raw materials. At high temperature, nitriding aluminum nitride superfine powder is successfully achieved with alumina used as aluminum source and ammonia used as nitrogen source. The effect on the nitridation reaction of the ammonia velocity, reaction temperature, holding time is also studied at the same time. The prepared powder was characterized by some analytical methods such as DTA-TG、XRD and TEM. The research conclusion are as follows:1. The preparation and doping modification of alumina powder(1) The alumina powder prepared by precipitation method experiences a process of phase transition as γ-Al2O3→δ-Al2O3→θ-Al2O3→α-Al2O3in the process of heating.(2) The alumina samples calcined at500℃is suitable for doping experiments. Because combined water has been removed, so it will not impact on the experiment, while the process of phase transition has not proceed. The samples calcined at500℃can be used as raw material of nitridation reaction which main phase is δ-Al2O3. (3) Doped lanthanum can significantly improve the phase transition temperature of alumina and the influence on δ-Al2O3is maximum. It can elevate stably exist temperature from1000℃to1200℃by doping lanthanum.(4) The inhibitory effect of doped lanthanum on agglomeration of alumina powder is more obvious at1000～1100℃. When the temperature is higher than1200℃, the inhibitory effect disappear and the particle size reach micron level.(5) The doped impurity elements can effect the experiment obviously, so impurity elements must be remove in the experiment.2. The preparation of aluminum nitride superfine powder(1) In nitriding reaction, sufficient ammonia is need to ensure that reaction is carried out fully. When the flow rate is too low, Alumina can not proceed nitridation reaction.(2) Contact area of powder and gas will affect the reaction rate, so powder must be spread out to ensure ammonia is contact with powder fully in the experiment.(3) Alumina powder will proceed nitridation reaction when the temperature is higher than1200℃before and after doping lanthanum. So doped lanthanum did not reduce the minimum temperature of nitridation reaction.(4) The reaction need to proceed for4h to ensure nitridation reaction is finished when the temperature is1400℃. It is difficult to prepare pure aluminum nitride when the temperature is below1400℃。There will still be a small amount of α-Al2O3when the reaction proceed10h at1350℃. Reaction time is too long and it is not conducive to the preparation of aluminum nitride superfine powder.(5) The nitridation reaction can proceed completely at1200℃for5h when lanthanum doped alumina is used aluminum source. The time reduce to3h when the temperature rose to1350℃.So doped lanthanum can significantly reduce the temperature of the nitridation reaction, speed up the nitridation reaction rate.(6) The particle size of prepared powder is small to meet the test requirements when nitridation temperature is lower than1300℃. The agglomeration of the particles occurs and the particle size increase significantly when the temperature is up to1400℃.