沉積條件對人工心瓣含硅低溫熱解炭微觀結構的影響
發(fā)布時間：2018-07-25 07:00
【摘要】：人工心瓣是人體病變心瓣的替代品，通過心瓣置換手術可以挽救患者生命。含硅低溫熱解炭具有良好的生物相容性、化學惰性、高強度、高耐磨等優(yōu)點，是人工心瓣的首選材料。國內外對熱解炭的研究大多集中在制備和性能測試方面，對微觀結構以及沉積機理的研究較少。關于應用在人工心瓣的含硅低溫熱解炭研究資料更是匱乏，因此非常有必要對其微觀結構進行研究。 本文采用準穩(wěn)態(tài)流化床化學氣相沉積工藝，在沉積溫度1250~1350oC，丙烷濃度25~60%的范圍內，控制其他參數(shù)不變，制備了六種含硅低溫熱解炭涂層樣品。通過X射線衍射儀、掃描電鏡、透射電鏡和密度儀，研究了各樣品的微觀結構；在前人研究基礎上，結合涂層微觀結構提出沉積機理；借沉積機理解釋了沉積溫度和丙烷濃度對其微觀結構的影響。主要研究內容如下： (1)研究了X射線衍射技術運用到熱解炭微晶結構測試方面需要注意的問題和解決方法，如峰形不對稱和穿透深度問題。發(fā)現(xiàn)單個樣品同一區(qū)域中熱解炭微晶結晶狀態(tài)連續(xù)分布在一個較差到相對較好的區(qū)間內；基體與涂層界面處熱解炭微晶石墨化度更高；隨著丙烷濃度的升高或者沉積溫度的降低，涂層中熱解炭微晶層間距增大、石墨化度降低、晶粒尺寸減小，碳化硅質量分數(shù)降低。 (2)掃描電鏡下含硅低溫熱解炭涂層由類球形顆粒和片層狀結構組成。透射電鏡下類球形顆粒從核心到最外圍的結構依次為：內核、多晶層、中高織構層、過渡層和無定形炭層。沉積條件變化通過改變片層結構和類球形顆粒的比例，以及類球形顆粒的融并情況，控制熱解炭的微觀形貌和密度。 (3)涂層密度在1.73~2.03g/cm3之間。片層狀結構和類球形顆粒的比例、類球形顆粒的融并情況以及共沉于熱解炭中的碳化硅的質量分數(shù)，共同決定最終制備的熱解炭涂層密度。 (4)提出相應沉積機理。氣相中：丙烷進入反應爐內生成C2H2等小分子以及芳香化合物；芳香化合物通過縮聚、化學吸附長大形成PAHs；PAHs通過化學吸附增加面積，物理吸附堆疊形成晶核；晶核長大成為液滴�；w表面：氣相生成的小分子直接沉積在基體表面得到片層狀結構（表面吸附生長）；液滴沉積在基體表面，融并、脫氫固化生成類球形顆粒結構（形核生長），，兩個過程相互競爭最終得到熱解炭。氣相中過早脫氫固化的液滴將以炭黑形式沉積。沉積溫度和丙烷濃度通過改變兩種沉積方式的比例以及液滴的大小和粘性來控制微觀結構。
[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.
【學位授予單位】：杭州電子科技大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TQ127.11;R318.11
本文編號：2143009
[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.
【學位授予單位】：杭州電子科技大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TQ127.11;R318.11
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本文編號：2143009
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