Translated Abstract
ABSTRACT
Aluminum nitride (AlN) is a kind of ceramic material with structure and function integration. AlN has great application prospect in many fields due to its excellent mechanical properties, high thermal conductivity, high electrical resistivity and low dielectric constant. Carbothermal reduction and nitridation (CRN) method is one of the main preparation methods for commercial AlN. The powder prepared by this method has the advantage of small particle size, uniform particle size distribution, good sphericity and good sintering properties. However the AlN powder prepared by this method in China has a large gap with the international advanced level, and the morphology, particle size and purity of the powder need further improvement. Therefore further research needs to improve the manufacturing process and reveal the synthesis mechanism. In this paper, we studied the preparation of AlN by conventional CRN method and precursor-carbothermal reduction and nitridation (PCRN) method, to reduce the cost through the selection of raw material and optimizing process parameters. The reaction mechanism and the properties of AlN powder by CRN and PCRN methods were also researched.
By using alumina (Al2O3) with different morphology and size as aluminum source and different kinds of carbon materials (carbon black and activated carbon) as carbon source, AlN powder was prepared by conventional CRN method under nitrogen atmosphere. The influence of aluminum source, carbon source and technical parameters on the purity and morphology of the AlN powder were investigated. The result showed that in the process of conventional CRN reaction, the morphologies of aluminum source and carbon source have little effect on the morphology of the final product. Spherical AlN powder can be obtained in the product. The purity of aluminum source had a great influence on the oxygen content of AlN product. The higher the purity of aluminum source was, the higher the purity of product was. Compared with carbon black, activated carbon can turn Al2O3 into AlN completely at lower temperature in the CRN process. The reaction temperature and time had a great effect on nitriding rate. By using activated carbon powder as carbon source and Al2O3 with purity of 99.99% as aluminum source, soaking at 1600℃ for 3h, pure spherical AlN with an average particle size of 0.6μm can be obtained. The heating rate had a great influence on powder morphology, when the heating rate increased from 8℃·min-1 to 2℃·min-1, the particle size significantly grown up. By DSC/TG analysis and calculation of the thermodynamic functions, it can be understood that gas phase Al2O(g) generate under low temperature and Al(g) generate under high temperature in the CRN process, and then the gas phases reacted with carbon and nitrogen to generate AlN.
With aluminum nitrate, urea, glucose as raw materials, the precursor with aluminum and carbon was firstly prepared by low temperature combustion method, Then the precursor was conducted by CRN method at high temperature under nitrogen atmosphere. Finally the sub-micron AlN was prepared successfully. For the PCRN method, pure AlN powder can be obtained at lower temperature. The effect of the temperature for preparing precursor, the urea content and glucose content on the purity and the morphology of the product were investigated, to obtain the optimal processing parameters. The results showed that when the molar ratio of aluminum source : carbon source : urea (Al/C/U) was 1:5.5:2, the precursor heated under 300℃，and then soaking at 1500℃ for 2h under nitrogen atmosphere of 0.2MPa, pure and spherical AlN with size an average particle size of about 0.5μm can be obtained. By DSC/TG and FT-IR analysis, it was known that precursor contained residual glucose, carbon and alumina. During the PCRN process the aluminum source and carbon source were mixed at the molecular level, so the nitriding temperature was low. Compared with CRN method, only Al2O gas was formed during the PCRN process
On this basis, the properties of the synthetic AlN powders by CRN and PCRN methods were compared with AlN powder imported from Japan and self-prepared AlN powder by combustion method. It can be found that the AlN powders, prepared by CRN and PCRN method had better sphericity, narrower particle size distribution, smaller particle size and better sintering performance than the other two. The as-synthesized AlN powders can be sintered compactly at low temperature. For example, for the AlN powder prepared by CRN method, the density of AlN bulk can reach 3.24g·cm-3 through the plasma activated sintering (PAS) process at 1500℃, and its thermal conductivity can reach 69.5W·m-1·K-1, which is considerable. For the AlN powder prepared by PCRN method, the density and thermal conductivity of AlN bulk can reach 3.27g·cm-3 and 46.4 W·m-1·K-1, respectively through the PAS process at 1450℃.
KEY WORDS: Aluminum nitride; Carbothermal reduction; Sintering; Mechanism
TYPE Of THESIS: Application Research
Translated Keyword
[Aluminum nitride, Carbothermal reduction, Mechanism, Sintering]
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