沉积条件对人工心瓣含硅低温热解炭微观结构的影响

发布时间：2018-07-25 07:00

【摘要】：人工心瓣是人体病变心瓣的替代品，通过心瓣置换手术可以挽救患者生命。含硅低温热解炭具有良好的生物相容性、化学惰性、高强度、高耐磨等优点，是人工心瓣的首选材料。国内外对热解炭的研究大多集中在制备和性能测试方面，对微观结构以及沉积机理的研究较少。关于应用在人工心瓣的含硅低温热解炭研究资料更是匮乏，因此非常有必要对其微观结构进行研究。本文采用准稳态流化床化学气相沉积工艺，在沉积温度1250~1350oC，丙烷浓度25~60%的范围内，控制其他参数不变，制备了六种含硅低温热解炭涂层样品。通过X射线衍射仪、扫描电镜、透射电镜和密度仪，研究了各样品的微观结构；在前人研究基础上，结合涂层微观结构提出沉积机理；借沉积机理解释了沉积温度和丙烷浓度对其微观结构的影响。主要研究内容如下： (1)研究了X射线衍射技术运用到热解炭微晶结构测试方面需要注意的问题和解决方法，如峰形不对称和穿透深度问题。发现单个样品同一区域中热解炭微晶结晶状态连续分布在一个较差到相对较好的区间内；基体与涂层界面处热解炭微晶石墨化度更高；随着丙烷浓度的升高或者沉积温度的降低，涂层中热解炭微晶层间距增大、石墨化度降低、晶粒尺寸减小，碳化硅质量分数降低。 (2)扫描电镜下含硅低温热解炭涂层由类球形颗粒和片层状结构组成。透射电镜下类球形颗粒从核心到最外围的结构依次为：内核、多晶层、中高织构层、过渡层和无定形炭层。沉积条件变化通过改变片层结构和类球形颗粒的比例，以及类球形颗粒的融并情况，控制热解炭的微观形貌和密度。 (3)涂层密度在1.73~2.03g/cm3之间。片层状结构和类球形颗粒的比例、类球形颗粒的融并情况以及共沉于热解炭中的碳化硅的质量分数，共同决定最终制备的热解炭涂层密度。 (4)提出相应沉积机理。气相中：丙烷进入反应炉内生成C2H2等小分子以及芳香化合物；芳香化合物通过缩聚、化学吸附长大形成PAHs；PAHs通过化学吸附增加面积，物理吸附堆叠形成晶核；晶核长大成为液滴。基体表面：气相生成的小分子直接沉积在基体表面得到片层状结构（表面吸附生长）；液滴沉积在基体表面，融并、脱氢固化生成类球形颗粒结构（形核生长），，两个过程相互竞争最终得到热解炭。气相中过早脱氢固化的液滴将以炭黑形式沉积。沉积温度和丙烷浓度通过改变两种沉积方式的比例以及液滴的大小和粘性来控制微观结构。
[Abstract]:Artificial heart valve is a substitute for human diseased heart valve. Low temperature pyrolytic carbon containing silicon has the advantages of good biocompatibility, chemical inertia, high strength, high wear resistance and so on, so it is the first choice material of artificial heart valve. Most of the studies on pyrolytic carbon are focused on the preparation and performance testing, but few on the microstructure and deposition mechanism. It is necessary to study the microstructure of silicon-containing low temperature pyrolytic carbon used in artificial heart valve. In this paper, six samples of silicon-containing pyrolytic carbon coatings were prepared by using quasi-steady state fluidized bed chemical vapor deposition process, in the range of 1250 ~ 1350oC, 2560% propane concentration, and without change of other parameters. The microstructure of each sample was studied by means of X-ray diffractometer, scanning electron microscope, transmission electron microscope and density meter. The effect of deposition temperature and propane concentration on the microstructure was explained by the deposition mechanism. The main contents are as follows: (1) the problems and solutions to the application of X-ray diffraction technique to the measurement of pyrolytic carbon microcrystal structure, such as peak asymmetry and penetration depth, are studied. It is found that the crystalline state of pyrolytic carbon microcrystals in the same region of a single sample is continuously distributed in a relatively good range, and the graphitization degree of pyrolytic carbon microcrystals is higher at the interface between substrate and coating. With the increase of propane concentration or the decrease of deposition temperature, the spacing of pyrolytic carbon microcrystalline layer increases, the graphitization degree decreases and the grain size decreases. The mass fraction of silicon carbide decreased. (2) the low temperature pyrolytic carbon coating containing silicon was composed of spherical particles and lamellar structure. The structure of spherical particles from the core to the periphery under TEM is as follows: core, polycrystalline layer, medium and high texture layer, transition layer and amorphous carbon layer. The microstructure and density of pyrolytic carbon were controlled by changing the lamellar structure, the proportion of spherical particles and the melting of spherical particles. (3) the coating density was between 1.73~2.03g/cm3. The ratio of lamellar structure to globular particles, the melting and merging of spherical particles and the mass fraction of silicon carbide co-deposited in pyrolytic carbon determine the density of the final pyrolytic carbon coating. (4) the corresponding deposition mechanism is proposed. In gas phase, propane enters into the reactor to form small molecules such as C2H2 and aromatic compounds. The nucleus grows into a droplet. Matrix surface: vapor generated small molecules deposited directly on the substrate surface to obtain lamellar structure (surface adsorption growth); droplets deposited on the matrix surface, melt, The structure of globular particles formed by dehydrogenation solidification (nucleation and growth), the two processes compete with each other to obtain pyrolytic carbon. Early dehydrogenation solidified droplets in the gas phase will be deposited in the form of carbon black. The deposition temperature and propane concentration control the microstructure by changing the ratio of the two deposition modes as well as the size and viscosity of the droplets.
【学位授予单位】：杭州电子科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ127.11;R318.11

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