Effect of Temperature on the Synthesis of SiC Coating on Carbon Fibers by the Reaction of SiO with the Deposited Pyrolytic Carbon Layer

The influence of reaction temperature on the preparation of SiC coating on carbon fibers by the reaction of silicon monoxide with the deposited pyrolytic carbon (PyC) layer has been discussed. With rising reaction temperature, the thickness of SiC layer increases and the SiC grain is coarsening. The apparent activation energy for the synthesis of SiC layer is about 103.3 kJ/mol. The oxidation resistance of carbon fiber can be improved by the SiC/PyC layers significantly. The initial oxidation temperature of the SiC/PyC coated carbon fiber is about 300°C higher than that of the uncoated carbon fiber. The oxidation of the SiC/PyC coated carbon fiber is owing to the diffusion of oxygen through the cracks generated by the mismatch of thermal expansion.     

Ti-O/Ti-N复合薄膜的离子束合成及人工心脏瓣膜材料表面改性研究

采用离子束增强沉积（ＩＢＥＤ）等方法在热解碳、钛及钴合金等人工心脏瓣膜材料表面制备Ｔｉ－Ｏ、Ｔｉ－Ｎ及其复合薄膜。对薄膜的成分、结构进行了研究，测定了材料的电阻率，对薄膜材料的血液相容性和力学性能进行了系统的研究。结果表明：合成薄膜具有优于热解碳的血液相容性和力学性能，提出了材料的血液相容性机理模型。     

n-C7H16/CCl4体系CVD-热解炭的形貌与形成机理

控制CVD工艺条件得到球状热解炭, 通过对沉积中间体的定性分析,证实了此过程中存在"缩聚机理". 运用热力学和晶体成核-长大理论,解释了温度对热解炭形貌和沉积过程的影响.     

Synthesis of silicon monoxide-pyrolytic carbon-carbon nanofiber composites and their hybridization with natural graphite as a means of improving the anodic performance of lithium-ion batteries

Novel composites of silicon monoxide, pyrolytic carbon and carbon nanofiber (SiO/PyC/CNF) were hybridized with natural graphite (NG) as a means of improving the anodic performance of Li-ion batteries. Samples were made with hybridization levels of 10-30?wt% of NG exhibited excellent cyclability with a discharge capacity of 389-522?mAh?g(-1) in a Li-ion battery system. SiO/PyC/CNF composite hybrids showed better cyclability than other carbon composites containing SiO/PyC and SiO/CNF. These hybridization effects were attributed to the lower contact resistance of SiO/PyC/CNF in the electrode. The internal spaces created throughout the SiO/PyC/CNF composite and their effect on material dispersion in the hybridized electrodes may have prevented electrode damage by relieving tensions induced by the expansion of SiO particles in the electrode over the course of repeated charge and discharge processes.     

Environmental Simulation Experiments of 3D-C/SiC Composites with Different PyC Interfacial Layers

A series of 3D-C/SiC composites with different pyrolytic carbon (PyC) interracial layers (about 20～300 nm thick)were prepared by chemical vapor infiltration.     

Characterization of pyrolytic carbon deposited on graphite substrates in inductive R.F. plasmas of propylene and argon

Coatings of pyrolytic carbon (PyC) on graphite substrates were obtained in an inductive r.f. plasma in mixtures of propylene and argon at pressures up to 10 Torr. The temperature of the graphite substrate in the inductive r.f. system was kept at 350 ± 50°C. The PyC coatings were analysed for anisotropy, for composition by small angle X-ray scattering and for density. The results obtained (varying the gas pressure and the propylene concentration in the r.f. plasma system) were partly compared with PyC coatings obtained in a chemical vapour deposition fluidized bed system.     

In Vivo and In Vitro investigation of titanium oxide layers coated on LTI-carbon by IBED

A layer of titanium oxide layer was coated on low temperature isotropic pyrolytic carbon (LTI-carbon), a prevailing material used for artificial heart valves' fabrication, by ion beam enhanced deposition (IBED). Glancing angle x-ray diffraction (GAXRD), X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectroscopy (RBS), atomic force microscopy (AFM) and transmission electronic microscopy (TEM) were used to characterize the deposited titanium oxide layer. The results show that the layer is polycrystalline with TiO, Ti₂O₃ and TiO₂ coexisting and the root-mean-square (RMS) roughness of the surface is measured to be 8.7 nm. Platelet adhesion experiments show that the adherent platelet on titanium oxide layer is about four times less than that on LTI-carbon. In vivo investigation was performed by implanting LTI-carbon and a titanium oxide layer coated LTI-carbon into the femoral artery of a dog for 4 weeks. By means of scan electron microscopy, coagulation, fibrin, deformed blood red cells and aggregation of adherent platelet were found on the surface of the uncoated LTI-carbon, whereas, nothing but a few normal-shaped blood red cells were found on the titanium oxide coated LTI-carbon. It can be concluded that titanium oxide coated LTI-carbon has a much better blood compatibility than that of the LTI-carbon.     

Interface engineering of fiber-reinforced all-oxide composites fabricated by the sol–gel method with fugitive pyrolytic carbon coatings

This paper describes the interface engineering of three–dimensional (3D) Nextel™440 fiber-reinforced aluminosilicate composites fabricated by the sol–gel method with fugitive pyrolytic carbon (PyC) coatings. The coating thickness on the fiber strength, interfacial characteristics and there corresponding effects on mechanical properties of the composites were investigated. The study shows that the fiber strength was influenced by the coating thickness and optimized with the thickness of 0.15 μm. The composites with uncoated fibers showed brittle fracture behavior without fiber pullout because of strong interactions between the fiber and the matrix. However, higher strengths and pseudo-ductile fracture behaviors were obtained in the composites with PyC interphases, where different deflections and branches of propagating cracks and fiber pullout patterns were observed. Moreover, induced fugitive PyC interface conditions have great effects on the density, microstructure and mechanical properties of the resultant composites.     

SiC/PyC复合涂层碳纤维微观结构及氧化行为研究

采用两步法在碳纤维表面制备了碳化硅/热解碳(SiC/PyC)复合涂层,PyC内涂层的制备采用等温化学气相渗透法,SiC外涂层的制备采用碳热还原法.借助X射线衍射、场发射扫描电镜、透射电镜分析了SiC/PyC复合涂层碳纤维的物相组成以及微观结构,利用热重分析研究了SiC/PyC复合涂层、PyC涂层以及无涂层碳纤维的氧化行为.结果表明,在碳纤维表面制备的SiC/PyC复合涂层连续致密、厚度均匀,PyC内涂层厚度约为200nm,SiC外涂层厚度约为160nm,SiC层中存在大量孪晶面高度有序的SiC孪晶.SiC/PyC复合涂层能够有效地改善碳纤维的抗氧化性能,较无涂层碳纤维起始氧化温度提高了近250℃.     

Enhancing both strength and toughness of carbon/carbon composites by heat-treated interface modification

A simple method to increase both strength and toughness of carbon/carbon (C/C) composites is presented. This method is based on the heat treatment of the pre-deposited thin carbon coating, leading to the formation of more orderly pyrolytic carbon (PyC) as a functional interlayer between fiber and matrix that could optimize the interfacial sliding strength in C/C composites. Effects of such a heat-treated PyC layers on the microstructure, tensile strength and fracture behavior of unidirectional C/C composites were investigated. Results showed that although the in-situ fiber strength was deteriorated after the introduction of interfacial layer, tensile strength of the specimen was greatly improved by 38.5% compared with pure C/C composites without any treatment. The interfacial sliding stress sharply decreased, which was interpreted from finite element analysis and verified by Raman spectra. Therefore, the fracture behavior was changed from brittle fracture to multiple-matrix cracking induced non-linear mechanical behavior. Finally, the ultimate strength can be predicted by different models according to the interfacial sliding stress. Our research would provide a meaningful way to improve both strength and toughness of C/C composites.     

MicroRaman spectroscopy of protective coatings deposited onto C/C–SiC composites

Abstract

MicroRaman spectroscopy has been used in the present work to investigate the structure and composition of pyrolytic carbon (PyC) and SiC protective coatings formed under various chemical vapour deposition conditions. Analysis of spectra obtained during Raman line mapping experiments on samples with graded Si_xC_y layer in the region of about 700–1000 cm^?1 allows information to be extracted on different SiC polytypes. It was found that the graded SiC layered sample contained a mixture of 3C–SiC and 6H–SiC polytypes at the film/substrate interface, but for the major part of this layer the 3C–SiC (β-SiC) phase predominates. For pure PyC films, it was found that the formation of PyC layer begins at 1200°C and the layer formed at this temperature is more uniform with slightly larger crystallite size (～3 nm) compared to that in the layer formed at 1300°C.     

Mechanical and electromagnetic wave absorption properties of C_f-Si_3N_4 ceramics with PyC/SiC interphases

Aiming to obtain microwave absorbing materials with excellent mechanical and microwave absorption properties, carbon fiber reinforced Si_3N_4 ceramics(Cf-Si_3N_4) with pyrolytic carbon(PyC)/SiC interphases were fabricated by gel casting. The influences of carbon fibers content on mechanical and microwave absorption properties of as-prepared Si_3N_4 based ceramics were investigated. Results show that chemical compatibility between carbon fibers and Si_3N_4 matrix in high temperature environment can be significantly improved after introduction of Py C/SiC interphases. As carbon fibers content increases from 0 to 4 wt%, flexural strength of Si_3N_4 based ceramics decreases slightly while fracture toughness obviously increases. Moreover, both the real and imaginary parts of complex permittivity increase with the rising of carbon fibers content within the frequency range of 8.2–12.4 GHz. Investigation of microwave absorption shows that the microwave attenuation ability of Cf-Si_3N_4 ceramics with Py C/SiC interphases is remarkably enhanced compared with pure Si_3N_4 ceramics. Effective absorption bandwidth(-10 d B) of10.17–12.4 GHz and the minimum reflection less of-19.6 d B are obtained for Si_3N_4 ceramics with 4 wt%carbon fibers in 2.0 mm thickness. Cf-Si_3N_4 ceramics with Py C/SiC interphases are promising candidates for microwave absorbing materials with favorable mechanical property.     

不同热解碳界面层厚度C/ZrC-SiC复合材料烧蚀性能及其机理

通过控制沉积时间制备S5-C/ZrC-SiC、S15-C/ZrC-SiC、S30-C/ZrC-SiC和S50-C/ZrC-SiC等不同热解碳界面层厚度的复合材料,研究了不同热解碳界面层厚度C/ZrC-SiC复合材料的密度与微观组织、烧蚀性能的变化规律及其机理。结果表明：随着热解碳界面层厚度的增大,C/ZrC-SiC复合材料SiC基体含量、密度和气孔率不断降低,但是裂解ZrC基体的含量表现出先降低而后增大的变化规律。S30-C/ZrC-SiC复合材料20 s短时间氧乙炔烧蚀性能最优,其质量烧蚀率和线烧蚀率分别-0.84 mg/s和3.00 μm/s;但是S15-C/ZrC-SiC复合材料长时间循环60 s烧蚀性能最优,其质量烧蚀率和线烧蚀率分别为1.22 mg/s和3.80 μm/s。其原因是,C/ZrC-SiC复合材料20 s氧乙炔烧蚀作用机理主要为机械冲刷,而C/ZrC-SiC复合材料的第二次60 s氧乙炔烧蚀发生了由机械冲刷向热物理和热化学烧蚀机理的转变。     

锂离子二次电池负极材料的发展

综述了锂离子二次电池负极材料的研究和进展。介绍了石墨,改性石墨,焦炭,热解炭和纳米级碳材料的研究,比较了各类碳材料的性质。也对锡基材料做了介绍,包括锡的氧化物,锡的复合氧化物和锡盐。同时还概述了其它的一些可以作为锂离子二次电池的负极材料。     

温度脉冲方法制备碳/碳化硅复合材料界面的微观结构与性能研究

采用温度脉冲化学气相渗透沉积的方法制备了碳/碳化硅复合材料界面. 以六甲基二硅胺烷(Hexamethyldisilazane , HMDS) 为前驱体, 以3k, 三维四向的石墨化碳纤维编织体为预制体, 通过强制流动热力学梯度化学气相渗透沉积的方法(FCVI)制备出密度为1.98g·cm^-3的C _f/SiC复合材料. 运用透射电子显微镜(TEM)对复合材料的界面微观结构进行了分析. 复合材料的平均弯曲强度为458MPa, 平均断裂韧性为19.8MPa·m^1/2. 应用扫描电子显微镜(SEM)对复合材料的断裂形貌进行了分析研究.     

化学气相沉积低温热解炭的微观组织结构与沉积模型

利用扫描电子显微镜(SEM),透射电子显微镜(TEM)结合选取电子衍射(SAED)研究了化学气相沉积低温热解炭的微观组织结构。结果表明:低温热解炭是由直径小于2μm的球形颗粒状炭组成,该球形颗粒状炭的核心是炭黑颗粒,外层为中织构热解炭。其沉积过程主要经历了:微小炭黑颗粒的萌生,炭黑颗粒外层的生长,炭颗粒表面热解炭的沉积和炭颗粒的聚集长大四个过程。     

疲劳氧化环境中3D SiCf/SiC复合材料损伤演变

研究了疲劳氧化环境中3D SiC_f/SiC复合材料损伤演变,并对该环境中SiC_f/SiC复合材料的失效机制进行了分析。结果表明,疲劳氧化环境中3D SiC_f/SiC复合材料的损伤主要为：基体开裂;热解碳界面相脱粘、氧化及取向性排列;纤维断裂、氧化及其结构的改变。这些损伤使氧化性气体通过基体开裂形成的裂纹不断氧化复合材料内部;界面相脱粘和取向性排列使纤维更容易拔出;纤维的氧化、纤维中无定形碳的增多以及SiC晶粒的长大导致纤维强度降低。     

Mechanical behavior of SiCf/SiC composites with alternating PyC/SiC multilayer interphases

In order to tailor the fiber–matrix interface of continuous silicon carbide fiber reinforced silicon carbide (SiC_f/SiC) composites for improved fracture toughness, alternating pyrolytic carbon/silicon carbide (PyC/SiC) multilayer coatings were applied to the KD-I SiC fibers using chemical vapor deposition (CVD) method. Three dimensional (3D) KD-I SiC_f/SiC composites reinforced by these coated fibers were fabricated using a precursor infiltration and pyrolysis (PIP) process. The interfacial characteristics were determined by the fiber push-out test and microstructural examination using scanning electron microscopy (SEM). The effect of interface coatings on composite mechanical properties was evaluated by single-edge notched beam (SENB) test and three-point bending test. The results indicate that the PyC/SiC multilayer coatings led to an optimum interfacial bonding between fibers and matrix and greatly improved the fracture toughness of the composites.     

Mo_2C改性C/C-Cu复合材料的组织及载流摩擦磨损性能

采用熔盐法在低密度炭/炭(C/C)坯体内孔表面制备了Mo_2C涂层,然后通过无压熔渗制备了C/C-Cu复合材料,研究了C/C-Cu复合材料的组织结构及载流摩擦磨损性能。结果表明:熔融Cu可自发渗入制备了Mo_2C内涂层的C/C坯体,复合材料中Cu相与C/C坯体形成相互贯穿的连通网络结构,Mo_2C涂层与Cu和热解炭(PyC)间均有良好的界面结合,反应生成Mo_2C过程中的催化石墨化及应力石墨化共同作用使C/C-Cu复合材料中Mo_2C涂层附近PyC的有序度提高。随载荷增大,C/C-Cu复合材料的摩擦系数逐渐降低,体积磨损率增大,而对偶的质量损失逐渐降低;载荷较大时材料磨损表面被摩擦膜覆盖的面积增大,但因粘着磨损摩擦膜的粗糙程度提高。材料磨损过程中还发生了氧化磨损,且载荷增大磨损表面O含量提高。     

Fabrication of short carbon fiber preforms coated with pyrocarbon/SiC for liquid metal infiltration

A novel method of fabricating short carbon fiber preforms was proposed for liquid metal infiltration. The preforms were shaped by wet forming and strengthened by pyrocarbon (PyC). SiC layers were prepared on carbon fibers by the reaction of SiO and PyC at 1600 °C. X-ray Diffraction, Scanning Electron Microscopy, and Energy Dispersive X-ray Spectroscopy were applied in the characterization of the preforms. Gas pressure infiltration was done to demonstrate the feasibility of the preforms for the liquid metal infiltration. The microstructure analysis indicates that carbon fibers are uniformly distributed in the preforms, and fibers are coated with an inner layer of PyC and an outer layer of SiC. The infiltration experiment proves that the prepared preforms are feasible for liquid metal infiltration under low infiltration pressure and temperature.