B4C--SiC/C复合材料氧化过程的TG/DTA分析

制备了Ｂ_４Ｃ－ＳｉＣ／Ｃ复合材料，对不同组成的复合材料在２０１５００℃升温氧化过程进行了ＴＧ／ＤＴＡ（热重和差热联用）分析。结果表明，复合材料具有不同的高温抗氧化性能，此差异可归因于以下几方面：复合材料的组成不同（包括陶瓷粒子的种类、含量），不同种类的陶瓷粒子氧化转变成陶瓷氧化物的温度、速率不同，生成的陶瓷氧化物在高温下的物性（对基体材料的润湿性、粘度及流动性、挥发性和对氧的扩散系数等）不同。通过在炭基体中弥散Ｂ４Ｃ粒子可明显提高炭基体在８５０℃以下的抗氧化性。当复合材料中Ｂ４Ｃ含量较高而ＳｉＣ含量低时，样品表面将趋于形成Ｂ２Ｏ３较为富集的硼硅酸玻璃相，在１５００℃以下具有良好的氧化防护效果；当样品中ＳｉＣ含量较高时，在高温下（＞１２００℃），随着部分Ｂ２Ｏ３的挥发和大量ＳｉＯ２的生成，样品表面将趋于形成ＳｉＯ２较为富集的硼硅酸盐玻璃相，在高达１４００℃以上仍具有良好的氧化防护效果

ANALYSIS OF ANISOTHERMAL OXIDATION BEHAVIOR OF B4C- SiC/C COMPOSITES USING TG/DTA TECHNOLOGY

Boron carbide-silicon carbide/carbon composites were preparedAnisothermal oxidation behavior of the composites with various compositions at the temperature of 201 500 was investigated by TG/DTA technologyResults show that the composites possess different oxidation resistance at elevated-temperaturethe reason for these should be attributed to several main factors as follows:the nature of ceramic particles and their content in the composites;the starting temperature of the ceramic particles oxidized into the ceramic oxide and the rate of the conversion;the performance of the ceramic oxide as a protection layer,such as the wetting ability to the carbon matrix,viscosity and mobility,volatility and the diffusivity of oxygen through the ceramic oxide layeroxidation resistance can be improved by introducing boron carbide particles into carbon substrate when the temperature is below 850 For the composites with higher boron carbide content and lower silicon carbide content,a borosilicate layer enriched in B 2O3 tends to form at the surface of the composites,which provides strong oxidation resistance below 1 200 For the composites with higher silicon carbide content,when the temprature was above 1 200 ,a borosilicate layer enriched in SiO2 tends to form at the surface of the composites with the volatilization of B2O3 and the formation of SiO2This kind of borosilicate layer provides high oxidation resistance of the composites up to 1 400