Joining of Carbon-Carbon Composites for Thermonuclear Fusion Applications

Carbon-fiber-reinforced carbon (CfC) composites have been joined by using different joining agents: metals (silicon, aluminum, and titanium), an intermetallic compound (magnesium silicide, Mg₂Si), and glasses (borosilicates and zinc borates). These joining agents have been chosen by considering their possible use in a thermonuclear fusion reactor, as suggested by their low-activation properties, reasonably high working temperature, industrial feasibility, and potential scale-up of the joined carboncarbon structures using pressureless-processing techniques. Each joined structure (CfC composite–joining material-CfC composite) has been first morphologically characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffractometry. Then, single-lap shear tests have been performed on the most-promising joined structures, i.e., silicon- and aluminum-joined CfC-composite samples, which have shown an average shear strength of 22 and 10 MPa, respectively.     

Thermophysical Properties of Carbon-Carbon Materials Based on Graphite Foam

Refractories and Industrial Ceramics - Low density heat-conducting carbon-carbon materials containing coke from 2.8 to 40 wt.% and with density varying in the range from 0.065 to 0.81 g/cm3 are...     

Notch Strength and Fracture Behavior of 2-D Carbon-Carbon Composites

This study examined Mode I in-plane fracture in two-directional carbon-carbon composites. Linear elastic fracture mechanics (LEFM) provided good predictions for the failure loads of the compact tension specimens, and consistent values of K _IC were calculated. However, values for the strain energy release rate G _IC were inconsistent. Analysis of loading/unloading cycles applied to the specimens showed that significant inelastic behavior occurred prior to fracture. Hence the J -integral method is not thought to be appropriate for fracture prediction. It was also found that the real crack tip stresses in carbon-carbon composites are much lower than theoretical predictions. An interesting discovery is that cracks in carbon-carbon composites appear to be naturally blunt. The lower limit on the crack tip diameter corresponds with the spacing of the woven fiber bundles. A significant conclusion from this study is that the material behavior can be modeled as the sum of two contributions: (i) a linear elastic solid, which fails according to LEFM, and (ii) an independent damage mechanism, which absorbs energy but does not alter the ultimate fracture load. Possible candidates for the damage mode are fiber pullout and inelastic deformations due to shear stresses.     

Alkaloid Synthesis via Gold-Catalyzed Carbon-Carbon Bond Formation Using Enamine-type Nucleophile

In this account, various types of cyclizations/cycloisomerizations of alkyne substrates with internal enamine-type nucleophiles including enamide, enaminone, enaminoester and in situ generated enamine in the presence of electrophilc transition metal catalysts (Pt, Rh, Cu, Au) are firstly introduced. Then, the applications of the gold-catalyzed reactions in the synthesis of an array of alkaloids are discussed. These natural products feature heterocyclic structural motifs such as pyridine, azaanthraquinone, pyridoacridine, pyrrole, indole, indolenine and carbazole, as well as chiral tetrahydroindolizine, azocine units and six-membered carbocycles bearing a quaternary carbon center.     

玻璃纤维及石墨增强聚四氟乙烯复合材料摩擦磨损性能的研究

用机械混合、冷压成型和烧结的方法制备了不同质量分数(5%~30%)的玻纤和石墨填充聚四氟乙烯(PTFE)复合材料制品。用M-2000型磨损试验机评价了不同样品在干摩擦下的磨损性能,揭示了填料玻纤和石墨对PTFE复合材料磨损性能的影响,并对磨损机理进行了探讨。用扫描电镜(SEM)对试样磨损形貌进行观察。结果表明:对玻纤进行改性能极大地提高PTFE复合材料的耐磨性能,同时可提高复合材料硬度;玻纤和石墨协同作用,对改善PTFE摩擦磨损性能有比较显著的效果;20%玻纤 10%石墨填充PTFE复合材料有着较好的摩擦磨损性能。     

石墨填充PP-HDPE复合材料的电性能研究

采用聚丙烯(PP)和高密度聚乙烯（HDPE）共混物为基体材料,以石墨为导电填料, 通过熔融共混法制备了导电复合材料。重点研究了石墨在两相基体中的分散情况以及复合体系的电学性能。扫描电镜测试结果表明:石墨粒子选择性的分散在共混物基体中,构成双渗流导电网络结构。电性能测试结果显示:在相同石墨含量下双基体体系的室温电阻率与GP/HDPE相比下降了1～4个数量级。同时,双渗流导电网络结构的存在部分消除了负温度系数（NTC）效应, 提高了热循环稳定性。     

原位膨胀熔融混合法制备聚乙烯/膨胀石墨插层型复合材料

以线形低密度聚乙烯(PE-LLD)、低温可膨胀石墨(LTEG)为原料,通过双转子连续混炼机,采用熔融混合法制备了PE-LLD/膨胀石墨插层型复合材料。通过扫描电镜（SEM）,X射线衍射(XRD)等表征方法对复合材料的结构和性能进行了分析,结果表明,石墨在与PE-LLD熔融混合过程中,发生了同步膨胀,并且PE-LLD分子链插入到石墨片层之间形成了插层型复合材料,相比纯PE-LLD,复合材料的阻隔性能提高了40 %。     

电化学合成聚苯胺-天然石墨复合材料工艺研究

通过单因素实验确定电化学合成聚苯胺-天然石墨复合材料工艺范围和操作条件,苯胺浓度为2.5 mol/L,硫酸浓度为3.0~5.0 mol/L,石墨质量浓度为0.5~1.0 g/L,聚合电流密度为0.16~0.18 A/dm2,t为3~5 min。并对复合膜层与本征态聚苯胺进行电导率测试,扫描电子显微镜观察和光谱仪红外表征。结果表明:聚苯胺-石墨复合材料的导电率有所提高,石墨掺杂到聚苯胺膜层中,改善了复合材料的性能。     

PE-HD／PANi／EG复合材料的制备

用过硫酸铵氧化原位聚合法成功制备了聚苯胺/膨胀石墨(PANi/EG)导电复合填料,用溶液法对高密度聚乙烯(PE-HD)填充复合,制备出PE-HD/PANi/EG复合材料,实现了PE-HD由绝缘体向半导体的转化。通过X射线衍射、扫描电镜、电导率测量对材料进行了表征,结果表明:PANi/EG复合填料XRD表征初级粒子尺寸小于28nm,SEM表征聚集体粒子尺寸约500nm左右,电导率高于0.5S/cm;复合导电填料质量分数为5%时,电导率达到10-10S/cm,接近抗静电材料的要求。     

Thermal Aging Properties of Graphite Fiber Reinforced Peek and Graphite Fiber Reinforced Bmi Composites

Graphite fiber reinforced poly(ether ether ketone) (PEEK) and graphite fiber reinforced bismaleimide (BMI) composite materials are two kinds of advanced fiber-reinforced polymer matrix composites with good thermal stability and excellent mechanical properties at high temperature. They are currently receiving considerable attention. the main limitation on their application is the lack of knowledge regarding their behaviors during extended use at high temperature. Thermal aging properties are the main parameters for new polymer matrix composites that will be used in advanced spacecraft structural components. From the results of thermal aging effects on the properties—including interlaminar shear strength, drop-weight impact strength, and impact energy—of graphite/PEEK and graphite/BMI composites, it is found that unidirectional graphite fiber reinforced composites retain higher strength compared to multidirectional, and that multidirectional graphite/PEEK composites keep higher property retentions than multidirectional graphite/BMI composites after thermal aging at 190°C. From scanning electron photomicrographs, it is also found that graphite/PEEK composites have better fiber/resin adhesion, intraply adhesion, and microcrack resistance compared to graphite/BMI composites after thermal aging.     

树脂/石墨导电复合材料的研究进展

阐述了国内外热固性及热塑性树脂/石墨导电复合材料制备方法的研究现状,以及石墨类型、制备工艺等因素对复合材料导电性能的影响,并对其发展前景进行了展望。     

聚乙烯/石墨阻燃复合材料的研究

研究了石墨、可膨胀石墨、膨胀石墨 /聚乙烯复合材料的阻燃性能。结果表明 ,石墨具有一定的阻燃作用 ,可膨胀石墨具有良好的阻燃效果。但可膨胀石墨填充的复合材料力学性能较差     

聚乙烯／膨化石墨导电复合材料的研究

研究了不同的工艺条件对聚乙烯/膨化石墨导电性能和力学性能的影响。结果表明，溶液插层法具有较低的导电渗滤阈值，但其力学性能也较差。     

Regulating the Interface in Graphite/Thermoplastic Composites

Among the many engineering thermoplastics available today, there exists a large subgroup of difficult-to-crystallize or amorphous polymers which possess a rather unique micronodular morphology in their normally produced solid state. When these polymers are processed in the unfilled state, changes in process thermal history have little effect on mechanical properties; but when reinforcement such as graphite is added, pronounced effects of thermal treatment arise which are relatable to the nodular polymer morphology. These effects will be documented and explained for graphite fiber-filled polycarbonate and poly(phenylene oxide). The practical application of these results to hot-forming techniques will also be described. Finally, extension of these techniques to the more easily crystallized thermoplastics such as polypropylene will be considered.     

聚乙烯/膨胀石墨导电阻燃复合材料的研究

通过溶液插层法研究了聚乙烯/膨胀石墨复合材料的力学性能、电学性能、阻燃性能。结果表明,当膨胀石墨填充量为10～15份时,复合材料的体积电阻降为1×108Ω以下,当膨胀石墨含量为30份时,复合材料的氧指数达到22 8,具有一定的阻燃性。     

聚丙烯基石墨导电复合材料研究进展

阐述了国内外聚丙烯基石墨导电复合材料制备方法的研究现状,以及石墨类型、界面相容剂和加工条件等因素对复合材料性能的影响,介绍了聚丙烯基石墨导电复合材料在制备双极板方面的应用进展,并对其发展前景进行了展望。