Handling and Surface Modificaiton pf Ultrafine Particles by CVD in Fluidized Bed Under Reduced Pressure

化学气相沉积法是一种非常有吸引力的制备超细颗粒的方法，具有可控的化学和结晶组成。最重要的因素之一是如何处理气相中的细颗粒。在这项研究中，流化，这是通常只用于粗颗粒，细化为超细颗粒的处理。(1)在0.1 ~ 100 kPa和25-200 ℃下，对粒径为30-400 nm的Si_3N_4、SiC、Al_2O_3和TiO_2颗粒进行流化，用光纤探针和安装在床内不同位置的压力传感器对流化床内的气泡、夹带和混合特性进行了评价。流化气为干燥空气或氮气，气速大于1cm/s。粘性颗粒也流化混合粗颗粒作为湍流促进剂。从颗粒物理化学性质的角度对流化性能进行了关联。(2)CVD处理实际上在直径为28 mm的实验室规模的流化床中进行。通过NH_3和TiCl_4反应在Si_3N_4或Al_2O_3表面镀导电TiN，通过NH_3和AlCl_3反应在Al_2O_3表面镀导热AlN。结果表明，流态化是CVD反应改性超细颗粒的有效方法。

Chemical vapor deposition method is very attractive to produce ultrafine particles with controlled chemical and crystalline compositions. One of the most important factors is how to handle fine particles in the gas phase. In this study, fluidization, which is normally used only for coarse particles, is refined for the handling of ultrafine particles.(1) Si_3N_4, SiC, Al_2O_3 and TiO_2 particles of 30-400 nm diameter were fluidized under 0.1-100 kPa and 25-200^ﾟC, and characteristics of bubbles, entrainment and mixing were evaluated by using optical fiber probes and pressure sensors equipped at various positions in the bed. The fluidization gas was dry air or nitrogen, and the gas velocity was larger than 1 cm/s. Cohesive particles were also fluidized by mixing coarse particles as the turbulent promoter. The fluidizability was correlated from the view of physicochemical properties of particles.(2) CVD processing were actually carried out in a bench-scale fluidized bed of 28 mm diameter. The coating of Si_3N_4 or Al_2O_3 with electro conductive TiN by the reaction of NH_3 and TiCl_4, and the coating of Al_2O_3 with thermo-conductive AIN by the reaction of NH_3 and AlCl_3 were among them. The results show that the fluidization is very effective to modify ultrafine particles by CVD reactions.