电磁场化学气相沉积制备各向同性热解炭及微观结构研究

【作者】 李建青；

【导师】 满瑞林； 黄启忠；

【作者基本信息】 中南大学 ， 化学工程， 2011， 硕士

【摘要】 本论文在课题组前期研究提出的电磁场化学气相沉积原理基础上,提出了微正压和负压化学气相沉积两种制备高密度块体各向同性热解炭材料的新型工艺。论文采用自行设计的化学气相沉积炉,以石墨为沉积基体、丙烯为碳源气体、氮气和氢气为稀释气体和载气,在温度为1000～1400℃C、丙烯流量范围为0.1～1.0L/min、氮气流量范围为0～15L/min、氢气流量范围为0～0.6 L/min、沉积时间为20h～40h的工艺条件下,制得平均密度为1.03～1.76g/cm3、厚度2～22mm的各向同性热解炭材料。利用X射线衍射仪、扫描电子显微镜、偏光显微镜、透射电子显微镜对所制得各向同性热解炭的石墨化度、断口形貌及微观组织结构进行了系统研究。结果表明,材料的石墨化度小于20%,其在偏振光下材料无任何光学活性和生长特征,符合各向同性热解炭的特征；材料存在孔径不等的微小孔隙,且随着材料密度的提高,孔隙形貌更加均匀、孔径更小。断口形貌表明,各向同性热解炭由直径100nm～3μm的球形或近球形颗粒状热解炭组成,且颗粒之间发生融并现象,融并范围随材料密度提高而增大。此外,考察了材料的显微硬度及抗弯和抗压强度。结果表明,材料的显微硬度、抗弯强度、抗压强度随材料的密度增大而增大。对影响各向同性热解炭沉积的关键参数—沉积温度和碳源气体浓度进行了考察,结合材料的微观结构分析及力学性能分析结果,得到微正压及负压工艺制备各向同性热解炭的优化工艺参数：微正压化学气相沉积工艺采用温度1300℃、丙烯流量0.2 L/min、氮气流量4 L/min、氢气流量0.6 L/min的工艺参数时,制备的材料密度达到1.76g/cm3,孔隙率为6.3%；负压化学气相沉积工艺采用温度1300℃、丙烯流量0.2 L/min、氮气流量0.3 L/min、氢气流量0.2 L/min的工艺参数时,制备的材料密度可达1.72g/cm3,孔隙率为5.5%。论文结合实验结果探讨了电磁场流态化制备各向同性热解炭的沉积原理,认为电磁场的存在促进了各向同性热解炭的沉积。更多还原

【Abstract】 The micro-positive pressure Chemical Vapor Deposition (CVD) and negative pressure CVD methods were proposed and employed for preparation of high density and bulk isotropic pyrocarbon on the basis of the principle of CVD in electromagnetic field which was proposed in the early research by our lab for the first time. With self-designed CVD furnace, using graphite as substrate, propylene as carbon source gas, nitrogen and hydrogen as carrier gas and dilution gas, the isotropic pyrocarbon products with average density from 1.03～1.76 g/cm3 and thickness from 5～22mm were fabricated, and the deposition conditions are as following:deposition temperature 1000～1400℃for 20～40h, propylene flow from 0.1～1.0 L/min, hydrogen flow from 0～0.6 L/min, and nitrogen flow from 0～15 L/min.The degree of graphitization, microstructure and surface morphology as well as fracture characteristics of pyrocarbon were studied by X-ray diffraction (XRD), polarized light microscopy (PLM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The results reveal that as-prepared pyrocarbon is optically isotropic and has no growth charaterization when its degree of graphitization is less than 20%. Pores with a variety of pore size distribute in the isotropic pyrocarbon. Moreover, the pore morphology gets more well-distributed and the pore diameter get smaller with the density of materials increasing. The fracture characteristics of isotropic pyrocarbon show that the isotropic pyrocarbon are mainly composed of the spherical pyrocarbon granules with diameter from 100nm～3μm, and spherical pyrocarbon granules more or less conglutinated with each other. With the increase of material’s density, the conglutinated area gets larger. The microhardness, flexural strength and compression strength of materials were also researched. It shows that the microhardness, flexural strength and compression strength of the products all get huger with the increase of material’s density.Deposition temperature and carbon source gas concentration which strongly influence the deposition of isotropic pyrocarbon were studied. And the optimization parameters for CVD isotropic pyrocarbon were obtained. While the deposition temperature was 1300℃, propylene flow 0.2L/min, hydrogen flow 0.6L/min and nitrogen flow 4L/min, the density of isotropic pyrocarbon fabricated by micro-positive pressure CVD method was 1.76 g/cm3. In contrast to micro-positive pressure CVD method, the isotropic pyrocarbon with the density 1.72 g/cm3 and the lowest porosity was obtained by negative CVD method under the conditions of the deposition temperature 1300℃, propylene flow 0.2 L/min, hydrogen flow 0.2 L/min and nitrogen flow 0.3 L/min.Combining the experimental results, a new deposition mechanism of isotropic pyrocarbon -electromagnetic field fluidization deposition mechanism was discussed. The presence of electromagnetic fields is considered to promote the deposition of isotropic pyrocarbon.更多还原