Preparation of Aluminum Nitride by Direct Nitriding of Large-Sized Aluminums

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Nitriding of aluminum has been generally performed for the atomized powder. In this work, the nitriding was studied by the use of aluminum chips with 2 mm in size.The mixtures of aluminum chips and atomized powder of aluminum were firstly caused to react with nitrogen. The nitriding of aluminum chips was completely accomplished at 1300ﾟC below 50% of chip content, adding Y(NO_3)_3・6H_2O.In addition, using a graphite reaction tube, Al chips without atomized powder were able to be nitrided with the maximum conversion of 99.3%.A lot of spherical shells with 2mm in size was observed in the product. Furthermore, fine powder of A1N with 1 mum in size was observed around the spherical shell. After the formation of spherical shells, rapid increase of temperature due to reaction heat was detected. Therefore, the nitriding process of Al chips was divided into two steps ; that is, in the initial step, molten Al chip reacts with N_2 on the surface to cover with AlN layr. At a high temperature, the generation of reaction heat is enough to vaporize the aluminum in the shell. This is the beginning of the second step. The aluminum vapor goes through the AlN layr to react with nitrogen gas outside of the shell. In this process, the initial step is very important for the nitriding. Y_2O_3, which is transformed from Y(NO_3)_3・6H_2O,may accelerate the nitriding in the initial step.Al wires with 2 mm in diameter and 50 mm in length were electrolytically etched to accelerate the nitriding in the initial step. The nitriding without Y_2O_3 was accomplished with the maximum conversion of 99.6%.In this work, the large-sized aluminums were successfully nitrided. This results will largely affect the process preparing AlN powders in the industry.