C/C–SiC composites derived from single-source poly(silylene–acetylene) precursors

Carbon-fiber-reinforced carbon–silicon carbide (C/C–SiC) composites were prepared by impregnating carbon fibers with ethynylphenyl-terminated poly(silylene–acetylene) (EPTSA) as a single-source precursor with subsequent hot pressing and pyrolysis. The structural evolution, crystallization behavior, and graphitization of bulk C–SiC ceramics, as well as their mechanical properties and ablation behavior, were investigated. The EPTSA precursor starts to transform into inorganic SiC ceramic materials at 800°C, which is characterized by an amorphous structure with weight loss, shrinkage, and densification between 800 and 1000°C. The formation of SiC crystals inhibited the growth of the graphitic structure between 1000 and 1200°C. As the temperature was raised, both graphite and SiC crystals continued to grow, and the crystalline forms became more complete. The carbon-fiber cloth (T300CF)-reinforced C–SiC composite (T300CF/C–SiC) prepared using polymer infiltration and pyrolysis (PIP) exhibited excellent mechanical properties. After five PIP cycles, the flexural strength, flexural modulus, and interlaminar shear strength of the T300CF/C–SiC composite reached 169 MPa, 32.5 GPa, and 9.38 MPa, respectively. In addition, the chopped-carbon-fiber-reinforced C–SiC composite fabricated using the PIP process demonstrated good oxyacetylene-torch ablation properties.     

Mechanical behavior of two-dimensional carbon/carbon composites with interfacial carbon layers

Effect of interfacial carbon layers on the mechanical properties and fracture behavior of two-dimensional carbon fiber fabrics reinforced carbon matrix composites were investigated. Phenolic resin reinforced with two-dimensional plain woven carbon fiber fabrics was used as starting materials for carbon/carbon composites and was prepared using vacuum bag hot pressing technique. In order to study the effect of interfacial bonding, a carbon layer was applied to the carbon fabrics in advance. The carbon layers were prepared using petroleum pitch with different concentrations as precursors. The experimental results indicate that the carbon/carbon composites with interfacial carbon layers possess higher fracture energy than that without carbon layers after carbonization at 1000°C. For a pitch concentration of 0.15 g/ml, the carbon/carbon composites have both higher flexural strength and fracture energy than composites without carbon layers. Both flexural strength and fracture energy increased for composites with and without carbon layers after graphitization. The amount of increase in fracture energy was more significant for composites with interfacial carbon layers. Results indicate that a suitable pitch concentration should be used in order to tailor the mechanical behavior of carbon/carbon composites with interfacial carbon layers.     

PAN基碳纤维中碳元素含量与纤维结构的关系

对聚丙烯腈(PAN)预氧化纤维进行碳化处理,制备了不同碳元素含量的PAN基碳纤维,利用元素分析、红外光谱、X射线衍射、拉曼光谱对纤维的元素组成、官能团结构及微晶结构进行了分析。结果表明:纤维中碳元素质量分数为67%~72%时,纤维内部官能团种类较多,石墨微晶较小;碳元素质量分数提高至93%后,纤维的红外谱图无吸收峰,微晶大小及石墨化程度大幅度提高。     

PA6/CF/EG导电复合材料的制备与性能

采用熔融共混法制备了不同碳纤维/热膨胀石墨(CF/EG)比例的尼龙6/碳纤维/热膨胀石墨(PA6/CF/EG)导电复合材料并研究其性能。结果表明,CF的加入能显著提高复合材料的力学性能;而随着EG含量的提高,复合材料的导电性能和导热性能显著提高,但力学性能在一定程度上得到降低。当CF质量分数为20%时,复合材料具有最优的力学性能,当EG质量分数为20%时,复合材料体积电导率可显著提高至0.262 S/m,热导率可达1.3379W/(m·K)。     

高温热处理对C/C多孔体显微结构的影响

以三维针刺碳毡作为预制体,先采用树脂单向加压浸渍结合热压固化制备了CFRP复合材料,然后通过树脂热解碳化制备出C/C多孔体。文章重点研究了高温热处理对C/C多孔体显微结构的影响。通过扫描电子显微镜观察了材料的显微结构,使用阿基米德方法测定材料的密度和气孔率,并利用压汞仪分析了材料的孔隙分布,利用X射线衍射分析碳基体的石墨化程度。结果显示,高温热处理后材料的密度降低,孔隙率增大;高温热处理没有改变材料中孔隙的类型,但使材料中三类孔隙尺寸均增大;经过高温热处理材料的石墨化度提高,部分块状碳基体转变为片层状石墨碳结构。     

Investigation of hot pressed ZrB2–SiC–carbon black nanocomposite by scanning and transmission electron microscopy

Hybrid ZrB₂-based composite having 10 vol% nano-sized carbon black and 20 vol% SiC was fabricated by vacuum hot pressing at 1850 °C under 20 MPa for 60 min. The microstructure and sinterability of the as-sintered ceramic was studied by X-ray powder diffraction, scanning electron microscopy, X-ray spectroscopy, scanning transmission electron microscopy and transmission electron microscopy analyses. A fully-dense hybrid composite could be achieved by hot pressing method under the aforementioned conditions. No new in-situ phase formation was detected after sintering process. Although the densification progressed in a non-reactive manner, the addition of carbonaceous material assisted the sinterability acting as the surface oxides cleaner. The precise phase and nanostructural investigations of the prepared ceramic verified the partial graphitization of carbon black and conversion of amorphous nano-additive into crystalline graphite nano-flakes.     

The catalytic effect of boric acid on polyacrylonitrile-based carbon fibers and the thermal conductivity of carbon/carbon composites produced from them

The catalytic effect of boric acid on the graphitization and surface structure of polyacrylonitrile-based carbon fibers was investigated by dipping fibers in boric acid before heating at 2500 °C. The thermal conductivity of carbon/carbon composites produced from the modified carbon performs by chemical vapor infiltration was also studied. The results show that the treatment by boric acid has a catalytic-graphitization effect on the fibers that increases the crystallinity and changes the surface state of carbon fibers during high temperature treatment. The modified carbon fibers induce the deposition of pyrocarbon with high crystallinity and an obvious transition interface between the carbon fiber and pyrocarbon during chemical vapor infiltration. By changing the microscopic structure of the carbon fibers, the interface bonding between fibers and pyrocarbon is improved and the microstructure of pyrocarbon is regulated. The thermal conductivity of the carbon/carbon composites is therefore improved, especially that in the direction perpendicular to fiber axis.     

Effect of fiber weight fraction on mechanical properties of carbon–carbon composites

This article presents the synthesis of carbon–carbon (C/C) composites by preformed yarn (PY) method, by varying the percentage of carbon fiber weight fraction. The PY used was carbon fiber bundle surrounded by coke and pitch which was enclosed in nylon‐6. Three types of samples with fiber weight fractions of 30, 40, and 50%, respectively, are fabricated and mechanical properties were studied. In each case, the PY was chopped and filled into a die of required shape and hot pressed at 500°C to get the preform composite. To obtain the carbonized and graphitic structure, the specimen was heat treated at 2500°C followed by soaking for 10 to 12 hrs. Further, two cycles pitch impregnation was done by hot isostatic pressing, to eliminate the voids and to increase the density hence to obtain good mechanical properties. The characteristics such as hardness, flexural strength, and impact strengths were studied. It is observed that, as the carbon fiber percentage increases, the properties also get improved, provided sintering is done at fairly higher temperatures such as 2700°C. The superiority of the new class of C/C composites made by the proposed PY technique over those obtained by the conventional methods is also demonstrated. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Finite element analysis and experiment study on the elastic properties of randomly and controllably distributed carbon fiber-reinforced hydroxyapatite composites

Randomly distributed carbon fiber-reinforced hydroxyapatite (RCF/HA) and controllably distributed carbon fiber-reinforced hydroxyapatite (CCF/HA) composites were firstly studied to design and prepare different required composite artificial bones with satisfying mechanical properties by combining experiment approach, theoretical prediction and finite element analysis (FEA). A plug-in was obtained by secondary development of ABAQUS for the FEA. A 3D representative volume element (RVE) for RCF/HA and CCF/HA can be easily generated using this tool. Stress and strain analyses of three directions of RVE were performed by ABAQUS with different fiber mass fractions and distributions. The elastic modulus of CF/HA composites were obtained. With 0.2 wt% fiber, the elastic modulus of RCF/HA and CCF/HA composites increased by 6.31% and 54.4% compared with that of HA, respectively. For CCF/HA composites, the elastic modulus increased significantly with the increasing fiber mass fraction in the E₁₁ of the fiber. The results of experiment study and theoretical prediction were consistent with that of FEA. The maximum error between the FEA and experiment study was 2.84%, which confirmed that the RVE model was rational and accurate. The results indicated the fiber distribution can greatly affect the elastic modulus of the composites. In the future study, the controllably distributed fiber–reinforced composites would be a good choice because they can improve the mechanical properties as required. This study would endow possibility of designing and preparing the CF/HA bio-ceramics with satisfied mechanical properties by FEA and proper preparation parameter. It would also speed up application of clinical practice for CF/HA composites.     

Ablation of the carbon/carbon composite nozzle-throats in a small solid rocket motor

Ablation of needled carbon/carbon (C/C) composite nozzle-throats was studied by hot-fire testing in a small solid rocket motor. The composition of the combustion gases was estimated by principle of free energy minimum. The ablation morphology was investigated by scanning electron microscopy. The ablation mechanism of C/C composites was also studied. The results showed that the ablation performance of C/C composites was determined by mechanical breakage of fibers/matrix together with thermal chemical ablation from the heterogeneous reactions on the throat surface. The mechanical breakage of fibers/matrix dominated the ablation of the composites at high pressure based on the calculated ablation rate. Cone-shaped fibers were formed after ablation in high fiber density area; but in low fiber density area, the fibers were peeled off because of the weakened strength after ablation. Meanwhile, the matrix around the fiber bundles was ablated into a shell shape, while the matrix between the cone-shaped fibers might be blown away by the combustion gases. Oxidation of C/C composites led to the formation of the cone-shaped fibers and shell-shaped matrix, as well as the loss of matrix between the cone-shaped fibers. The fiber/matrix fragments on the ablation surface were caused by the mechanical breakage.     

Thermoelastic behavior of carbon fiber/polycarbonate model composites

Model composites of polycarbonate (PC) containing single, multiple and chopped carbon fibers (CF) with and without and epoxy sizing were prepared by hot pressing. The thermoelastic behavior of model CF/PC composites was characterized by stretching calorimetry at room temperature. For small strains ? (i.e., ? ≈ 0.01) the specific mechanical work, specific heat effects and specific internal energy changes ΔU were completely reversible in stretching/contraction cycles and quantitatively obeyed the standard relationships for elastic solids. Young's moduli E and ΔU were significantly higher, whereas the linear thermal expansivities α_L were lower for model CF/PC composites compared to those for the neat PC. Smaller values of the above parameters for composites reinforced with sized CF suggested weaker CF/PC interfacial interactions. Current theoretical models of thermoelastic properties of composite materials suggest the existence of unusually stiff, highly oriented PC structures in fairly thick boundary layers around CF. The onset of inelastic deformation, as well as mechanical failure in CF/PC model composites at significantly smaller strains compared to the neat PC were tentatively explained by the yield and subsequent plastic flow of the matrix polymer initiated by heat effects of fiber fragmentation processes, and by higher concentration of microvoids generated in fiber fragmentation/debonding events, respectively.     

Influence of graphitization temperature on microstructure and mechanical property of C/C-SiC composites with highly textured pyrolytic carbon

C/C-SiC composites with highly textured pyrolytic carbon (HT PyC) were prepared by a combining chemical vapor infiltration and liquid silicon infiltration. The effect of HT PyC graphitization before and after 2327 and 2723 K on C/C-SiC composites was investigated. The mechanical properties decreased with increasing graphitization temperature, but graphitization treatment changed the fracture behavior from brittle like to pseudo-ductile. The decrease in bending strength from 306.21 to 243.69 MPa resulted from the weak interfacial bonding between HT PyC and fiber, and the good orientation of graphite layers. The crack at border of fiber bundle and longitudinal crack in HT PyC shortened the path of crack propagation, resulting in fracture toughness decrease from 21.11 to 14.72 MPa·m^1/2. A more pseudo-ductile behavior was due to the longer pull-out of fibers, the better orientation of graphite layers, the sliding of sublayers, and the deflection and propagation caused by the transverse cracks.     

Erosion of carbon/carbon composites using a low-velocity,high-particle-concentration two-phase jet in a solid rocket motor

The erosion of a four-direction carbon/carbon composite test piece using a low-velocity, high-particle-concentration two-phase jet was studied by the hot firing test of a small solid rocket motor with an elaborately designed flow path. The linear ablation rates were measured. The ablation surface and microstructure of the carbon/carbon composites were studied by scanning electron microscopy, and the ablation mechanism was investigated. Within the parameter range studied in this paper, mechanical erosion is found to play a dominant role in the ablation of carbon/carbon composites in the impact region. Moreover, the effect of chemical ablation is weak. The erosion of carbon/carbon composites results in blunt fracture tip fibers and a lamellar matrix. The particle impact mass flux is more dominant than the particle impact velocity in the erosion of carbon/carbon composites. At mesoscale, the carbon rods are more resistant to mechanical erosion than fiber bundles. At microscale, the carbon fibers are more susceptible to mechanical erosion than the carbon matrix, whereas the carbon fibers are more resistant to chemical ablation than the matrix and interface.     

Enhanced mechanical,thermal and ablation properties of carbon fiber/BPR composites modified by mica synergistic MoSi2 at 1500 °C

Ablation material had been widely used in aerospace attributed to its reliability and strong adaptability but was usually accompanied by low strength at higher temperatures. Here, a high flexural strength of 66.91 MPa after ablation at 1500 °C of carbon fiber/boron phenolic resin (CF/BPR) composite modified by MoSi₂ and mica was reported. With the proportion of MoSi₂ and mica was 9:1, the formed appropriate content of the liquid phase improved the reactivity of MoSi₂ powders and provided a suitable interfacial state between CF and the matrix. The result of the oxygen-acetylene test showed that the mass ablation and the linear ablation reduced to 0.034 g/s and 0.006 mm/s, respectively. Owing to the formed liquid phase wrapping the carbon fiber and ceramic layer on the surface improved the ablation resistance. These high-strength CF/BPR composites have strong potential in new aerospace materials.     

Microstructure and fracture behavior of (co)injection‐molded polyamide 6 composites with short glass/carbon fiber hybrid reinforcement

The mechanical and fracture properties of injection molded short glass fiber)/short carbon fiber reinforced polyamide 6 (PA 6) hybrid composites were studied. The short fiber composites of PA 6 glass fiber, carbon fiber, and the hybrid blend were injection molded using a conventional machine whereas the two types of sandwich skin–core hybrids were coinjection molded. The fiber volume fraction for all formulations was fixed at 0.07. The overall composite density, volume, and weight fraction for each formulation was calculated after composite pyrolysis in a furnace at 600°C under nitrogen atmosphere. The tensile, flexural, and single‐edge notch‐bending tests were performed on all formulations. Microstructural characterizations involved the determination of thermal properties, skin–core thickness, and fiber length distributions. The carbon fiber/PA 6 (CF/PA 6) formulation exhibits the highest values for most tests. The sandwich skin‐core hybrid composites exhibit values lower than the CF/PA 6 and hybrid composite blends for the mechanical and fracture tests. The behaviors of all composite formulations are explained in terms of mechanical and fracture properties and its proportion to the composite strength, fiber orientation, interfacial bonding between fibers and matrix, nucleating ability of carbon fibers, and the effects of the skin and core structures. Failure mechanisms of both the matrix and the composites, assessed by fractographic studies in a scanning electron microscope, are discussed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 957–967, 2005     

Flammability and thermomechanical properties of dianhydride‐modified polybenzoxazine composites reinforced with carbon fiber

Composites based on carbon fiber (CF) and benzoxazine (BA‐a) modified with PMDA were investigated. The flammability of the carbon fiber composites was examined by limiting oxygen index (LOI) and UL‐94 vertical tests. The LOI values increased from 26.0 for the CF/poly(BA‐a) composite to 49.5 for the CF‐reinforced BA‐a/PMDA composites as thin as 1.0 mm and the CF‐reinforced BA‐a/PMDA composites were also achieved the maximum V‐0 fire resistant classification. Moreover, the incorporation of the PMDA into poly(BA‐a) matrix significantly enhanced the T_g and the storage modulus (E') values of the CF‐reinforced BA‐a/PMDA composites rather than those of the CF/poly(BA‐a). The T_g values and storage moduli of the obtained CF‐reinforced BA‐a/PMDA composites were found to have relatively high value up to 237°C and 46 GPa, respectively. The CF‐reinforced BA‐a/PMDA composites exhibited relatively high degradation temperature up to 498°C and substantial enhancement in char yield with a value of up to 82%, which are somewhat higher compared to those of the CF/poly(BA‐a) composite, i.e., 405°C and 75.7%, respectively. Therefore, due to the improvement in flame retardant, mechanical and thermal properties, the obtained CF‐reinforced BA‐a/PMDA composites exhibited high potential applications in advanced composite materials that required mechanical integrity and self‐extinguishing property. POLYM. COMPOS., 34:2067–2075, 2013. © 2013 Society of Plastics Engineers     

PPy/CS复合电极热压成型条件的优化

以壳聚糖（CS）和聚吡咯（PPy）制备的复合材料为活性基体,在不添加黏结剂的条件下,采用热压成型法制备复合电极。重点考察了不同导电剂对电极力学性能的影响,热压温度、成型压力、热压时间及不同种类活性炭对电极电化学性能的影响规律。结果表明：通过热压法不添加黏结剂能够获得性能优良的复合电极;以活性炭为导电剂的电极溶胀性和亲水性最好,且活性炭的比表面积越大电极的电化学性能越好;电极热压成型的最优条件为：热压温度150℃、成型压力10 MPa、热压时间20 min。     

Catalyst optimization and reduction condition of continuous growth of carbon nanotubes on carbon fiber surface

Carbon nanotubes (CNTs)/carbon fiber (CF) reinforcements were synthesized under different catalyst compositions and reduction conditions. The effects of the catalyst, reduction temperature and reduction time on the surface morphology, graphitization, and single filament tensile strength of the prepared CNTs/CF samples were investigated. When nickel was used as the catalyst and copper as the catalyst promoter, with the increase of copper concentration, the catalytic activity increased. Thus, the carbon source was consumed more completely, improving the abundance of CNTs with good graphitization. And the effect of repairing CF defects was more obvious, hence the single filament tensile strength accordingly increased. Besides, the increase of catalyst reduction temperature and reduction time intensified the etching of CF by catalyst, and decreased the single filament tensile strength of CF. With the deposition of CNTs, the tensile strength of CF was enhanced in varying degrees. When the concentration of cooper was 0.01 mol/L with the reduction time of 10 min and reduction temperature of 450 °C, CNTs/CF had the highest tensile strength, which can reach up to 4.51 GPa. We determined that bimetallic catalysts could adjust the catalytic activity of nickel. The change of reduction time and temperature would affect the quality of CNTs, which was helpful to obtain high quality CNTs on CF surface and improve the mechanical properties of CNTs/CF and its composites.     

Effect of incorporation of carbon fiber and silicon carbide powder into silicone rubber on the ablation and mechanical properties of the silicone rubber‐based ablation material

This study examined the effects of the incorporation of carbon fiber (CF) and silicon carbide powder (SCP) into a high temperature vulcanized (HTV) silicone rubber, poly(dimethylsiloxane) (PDMS) containing vinyl groups on the ablation properties using an oxy‐acetylene torch test. The ablation test results showed that CF enhanced the hardness of the char formed on the composite surface during the oxy‐acetylene torch test and was an important factor determining the ablation properties. SCP was also beneficial in enhancing the surface char hardness of the HTV/CF composite. A new method was devised to evaluate the ablation properties more objectively by measuring the time elapsed for a rectangular‐shaped silicone rubber composite with specimens loaded with a constant weight to burn and fail off during the oxy‐acetylene torch test. The mechanical properties of the silicone rubber composites were also examined as a function of the additive content using a universal test machine (UTM). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Improving the performance of carbon composites by liquid phase activated sintering of MCMBs doped with Ti/Ni or Fe/Ni

A novel fabrication method for carbon composites using liquid phase activated sintering at 1400 °C in vacuum is described. Specimens for testing were prepared by subjecting mixtures of mesocarbon microbeads (MCMBs), Ti/Ni or Fe/Ni powders, and suitable additives, to aqueous tape casting, and molding the tapes into laminates prior to sintering. After sintering XRD showed that there were some eutectic liquid phases formed in the composites, which were favorable to enhancing the densification and reducing the porosity of the carbon composites. The reduction of the interlayer spacing of graphite crystallites due to the addition of the binary metal particles showed that the formation of the eutectic liquid promoted graphitization. The results showed that both the bend strength and the electrical conductivity of the carbon composites were also improved with the addition of the binary metal mixture.