Preparation Of Insulative And Heat-conductive Ceramic Coatings On Graphite

Based on low thermal resistance packaging technology for high-power LED devices, this paper explored the technology of preparing insulative and heat-conductive multiphase ceramic coatings on the surface of graphite matrix.(1) AIN-Al2O3·B2O3-SiC coating.(2) Si3N4-SiC coating.Firstly, composite slurry of H3BO3、AlN powder and monatomic silicon powder was prepared though ball milling to coat on the surface of graphite matrix. With the technology of powder bed, AIN-Al2O3·B2O3-SiC multiphase ceramic coatings was synthesized successfully. Monatomic silicon powder was chosen as the raw material for Si3N4-SiC coating. The slurry of silicon powder after ball milling was coated to the surface of graphite matrix. Si3N4-SiC coating was successfully synthesized when heat treatment in nitrogen was employed. Systimaticly reserched the impact of different process conditions on the synthesis of coating and the interface bonding behaviour of coating and matrix. And reserched the properties of multiphase ceramic coatings.As for AlN-Al2O3·B2O3-SiC multiphase ceramic coatings, it has smooth surface when it was keep in1400℃for2h with the powder bed sintering process was applied in heat trezhiatment. The main phase of the coating is AIN、SiC and Al-B-O, the strcture of the coating was compact, finely combined with the matrix, no flaws or pores were found.The temperature of heat treatment has a big influence on the synthesis of the coating. Pores were found when the maximum temperature was1450-1500℃; The ratio of the raw material has little impact on the compositon of the coating. But it has a big influence on the surface morphology, with the decrease of the ratio of Si/Al, flaws appeared.Nanometer impression test of the sample heat-treated in1400℃for2h showed that the nanometer hardness was7.7Gpa, and the modulus of elasticity was128.3Gpa. The method of electrical resistivity test was designed by the author, and the electrical resistivity was3.6×107Ω·m.This paper did some preliminary study on the synthesize process of Si3N4-SiC multiphase ceramic coating, and some preliminary analysis on the surface morphology.The process of the heat treatment had a big influence on the phase of the coating. The main phase of the coating kept for2h when it was sintered with powder bed process to1500℃was SiC; The main phase of the coating sintered in nitrogen to1450℃was Si3N4、SiC and silicon remining. sintered the sample which had been sintered in1450℃in nitrogen to1500℃, the main phase was Si3N4、SiC. The coating sintered twice has very compact structure and fine combination with the matrix.