【作者】 龙海波；

【导师】 张宁；

【作者基本信息】 沈阳大学 ， 材料加工工程， 2007， 硕士

【摘要】 SiC陶瓷具有优良的高温力学性能,抗氧化性强、耐磨损性好、热稳定性佳、热膨胀系数小、热导率大、硬度高以及抗热震和耐化学腐蚀等优良性能,被广泛应用于精密轴承、密封件、气轮机转子、燃烧喷嘴、热交换器部件及原子热反应堆材料等,并日益受到人们的重视,应用前景十分广阔。目前,SiC粉体的商业化生产以二氧化硅和炭黑为原料采用碳热还原法为主。此工艺方法一般需要很高的温度（﹥1600℃）和较长的时间（﹥5h）,这不仅使颗粒尺寸长大,而且使SiC粉体的生产成本增高,极大地影响了SiC粉体的推广和应用。众多研究表明,提高反应物起始原料的均匀混合程度、添加适量的添加剂是改善碳热还原法制备SiC超细粉体的有效途径。本文以纳米SiO₂和活性炭为起始原料,以稀土镧或铈为添加剂,采用碳热还原法制备SiC超细粉体。实验结果表明:以稀土镧为添加剂时,在1500℃×120min合成工艺下,可以合成出一次粒径为100nm左右,二次粒径为360nm的SiC细粉,且SiC粉体颗粒形状规则,无团聚,分散性好;以稀土铈为添加剂时,在1500℃×150min合成工艺下,也可以得到单相的SiC,但SiC粉体颗粒形状不规则,有大量晶须存在,且团聚严重。表明在碳热还原法制备SiC粉体的过程中,稀土镧的作用要强于稀土铈。与传统碳热还原方法相比,利用稀土镧为添加剂的碳热还原方法,不但降低了SiC粉体的合成温度,大大缩短了反应时间,而且可以制备出颗粒形状规则,无团聚的超细SiC粉体。本文还对碳热还原法合成SiC的反应机理进行了初步探索。认为碳热还原法合成SiC粉体有两种反应机理:一种是在密闭的容器内,通过控制合成温度和调整CO气体的分压,可使合成SiC的反应按气—气相方式进行;另一种是在流通的Ar气氛中,合成SiC的主要反应只能按气—固相方式进行。SiC颗粒的生成也可通过两种方式进行,一是SiO和CO气体直接在气相中反应生成极其细小的SiC粉体;二是活性炭孔隙先吸附SiO气体,然后与其发生反应生成SiC,SiC在活性炭的孔隙中成核和长大,所以活性炭孔隙的形状和大小决定了SiC颗粒的形状和大小。更多还原

【Abstract】 SiC ceramic has been extensively applied in precision bearings, sealing element, steam-turbine rotor, burner nozzle, heat interchanger parts, atomic reactor materials and etc. because of its excellent properties in high temperature mechanical properties, antioxidatio, abrasion resistance, thermal stability, smaller coefficient of thermal expansion, larger thermal conductivity, hardness, thermal shock and chemical corrosion. It has attracted increasing attention in recent years and has a wide application foreground. At present, the main method to synthesize SiC powder for trade—carbonthermal reduction method need high temperature (﹥1600℃) and long time (﹥5h), which not only increases the size of the powder but also enhances the production cost that largely affect the spreading and application of SiC powder.Many research indicated that improving the homogeneous mixing extent of the starting materials and adding appropriate additives were the effective ways to accelerate the reaction rate. In this paper, nano-SiO2 and activated carbon were used to synthesize SiC powder by carbonthermal reduction method. The rare earth lanthanum or ceria were used as the additives. The experimental results showed that SiC ultrafine powder was synthesized at 1500℃for 120 minutes by used rare earth lanthanum as additive. Its primary particle size was about 100nm and aggregated particle size was about 360nm and the particle shape was regulation, non-aggregation and well dispersibility. While the rare earth ceria used as the additive, SiC ultrafine powder was synthesized at 1500℃for 150 minutes but the particle shape was irregulation and seriously agglomerated and had numerous crystal whiskers. The results indicated that the effect of lanthanum was better than ceria in the process of synthesize SiC by carbonthermal reduction method. Comparing with the traditional carbonthermal reduction method, the synthesis temperature was not only reduced, but also the time of reaction was shortened. Therefore, ultrafine powder of SiC could be produced with non-aggregation and regulate particle shape. In this paper, the reaction mechanism for synthesize SiC powder by carbonthermal reduction method was also discussed. There were two reaction mechanisms: for first, if the reaction happens in a closed vessel, the reaction between the gas and gas phase would be happened through controlling the synthetic temperature and adjusting the partial pressure of CO. for second, if the reaction happens in the atmosphere of Ar the reaction between the gas and更多还原