Porous carbon/carbon composites produced from carbon black and petroleum pitch

Granular porous carbon/carbon composites were prepared by mixing carbon black, petroleum pitch and a solvent, followed by granulating the mixture and carbonization of the resulting pellets in an inert atmosphere. The pore structure of this material is studied by mercury porosimetry and scanning electron microscopy. Based on the obtained results, a model for it is proposed. The effects of carbon black type used, filler/binder ratio, heat treatment temperature and mixing time on surface area, total pore volume and strength of the finished pellets were investigated. Comparison with activated carbons indicates that the investigated material can find industrial applications as a catalyst support and as an adsorbent for adsorption of large molecules due to the meso- and macroporous structure and low ash content.     

Oxidation and carbonization in the preparation of carbon fibres from petroleum pitch

Conclusions -- Gaseous and resinous products are evolved in the thermo-oxidation of spun pitch fibres. The main components of the gas are H₂O, CO, and CO₂. The effect of rate of temperature elevation, velocity of the air stream, and the duration and temperature of thermo-oxidation on the amount of evolved oxidation products, and oxygen content and sample weight gain have been investigated.-- The kinetics of evolution of H₂, CO, CH₄, and CO₂ has been studied in the carbonization of spun and oxidized pitch fibres. It has been shown that during temperature elevation CO₂ is initially evolved, and then CO and CH₄. H₂ is evolved at temperatures of 540°C and higher.Bashkirskii State University. Translated from Khimicheskie Volokna, No. 3, pp. 37–38, May–June, 1991.     

Single-walled carbon nanotube buckypaper and mesophase pitch carbon/carbon composites

Carbon/carbon composites consisting of single-walled carbon nanotube (SWCNT) buckypaper (BP) and mesophase pitch resin have been produced through impregnation of BP with pitch using toluene as a solvent. Drying, stabilization and carbonization processes were performed sequentially, and repeated to increase the pitch content. Voids in the carbon/carbon composite samples decreased with increasing impregnation process cycles. Electrical conductivity and density of the composites increased with carbonization by two to three times that of pristine BP. These results indicate that discontinuity and intertube contact barriers of SWCNTs in the BP are partially overcome by the carbonization process of pitch. The temperature dependence of the Raman shift shows that mechanical strain is increased since carbonized pitch matrix surrounds the nanotubes.     

Influence of surface modification of carbon nanotube on microstructures and properties of polyamide 66/multiwalled carbon nanotube composites

The melt‐mixing polyamide 66 (PA66) composite samples that incorporated pure, acid‐ and amine‐functionalized multiwalled carbon nanotubes (MWCNTs) were prepared in order to enhance mechanical and frictional properties of PA66 composites. The homogeneous dispersion of amine‐functionalized MWCNTs (D‐MWCNTs) in PA66 matrix was observed from the significantly uniform morphology of tensile fractured surface of the composites. Differential scanning calorimetry measurement indicates that D‐MWCNTs acted as effective nucleation agent for PA66 matrix and the crystallinity of PA66 was increased. The fracture stress and tensile modulus of the composites were significantly improved with the incorporation of D‐MWCNTs, owing to the good dispersion of D‐MWCNTs. Compared with PA66, the PA66 composites with 1.0 wt% D‐MWCNTs were improved considerably in both wear and friction properties owing to the change of the tribological mechanisms. The good dispersion of D‐MWCNTs in PA66 and good interface compatibility between D‐MWCNTs and PA66 favored the formation of a thin layer on the contact surfaces during wear and friction test, which played an important role in reducing wear and friction of the composite and in suppressing the transverse cracks. These results prove the importance of D‐MWCNTs in a positive change of the mechanical and frictional properties of PA66 composites and suggest the applicability prospect of PA66/D‐MWCNTs composites in engineering components.POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Thermophysical properties of densified pitch based carbon/carbon materials—II. Bidirectional composites

Bidirectional carbon/carbon composites were developed using high-pressure impregnation/carbonization technique with PAN based carbon fabric as reinforcement and coal tar and synthetic pitches as matrix precursors. Microstructure of these composites has been evaluated using scanning electron microscope and polarized light optical microscope. Thermophysical properties i.e. thermal conductivity and specific heat have been evaluated both at room temperature and between 40 and 300 °C. The temperature dependence of thermal diffusion, specific heat and thermal conductivity has been studied and correlated with microstructure of carbon/carbon composites. It is found that the specific heat of carbon/carbon composites shows increase with temperature with an inverse slope in the temperature range of 150-200 °C. Accordingly, though the thermal conductivity decrease with temperature due to increased phonon interactions, it shows reversible action between 150 and 200 °C.     

In situ preparation of polyimide/amino‐functionalized carbon nanotube composites and their properties

In order to improve the dispersion of carbon nanotubes (CNTs) in polyimide (PI) matrix and the interfacial interaction between CNTs and PI, 4,4′‐diaminodiphenyl ether (ODA)‐functionalized carbon nanotubes (CNTs‐ODA) were synthesized by oxidation and amidation reactions. The structures and morphologies of CNTs‐ODA were characterized using Fourier transform infrared spectrometer, transmission electron microscopy, and thermal gravimetric analysis. Then a series of polyimide/amino‐functionalized carbon nanotube (PI/CNT‐ODA) nanocomposites were prepared by in situ polymerization. CNTs‐ODA were homogeneously dispersed in PI matrix. The influence of CNT‐ODA content on mechanical properties of PI/CNT‐ODA nanocomposites was investigated. It was found that the mechanical properties of nanocomposites were enhanced with the increase in CNT‐ODA loading. When the content of CNTs‐ODA was 3 wt%, the tensile strength of PI/CNT‐ODA nanocomposites was up to 169.07 MPa (87.11% higher than that of neat PI). The modulus of PI/CNTs‐ODA was increased by 62.64%, while elongation at break was increased by 66.05%. The improvement of the mechanical properties of PI/CNT‐ODA nanocomposites were due to the strong chemical bond and interfacial interaction between CNTs‐ODA and PI matrix. POLYM. COMPOS., 35:1952–1959, 2014. © 2014 Society of Plastics Engineers     

Thermophysical properties of densified pitch based carbon/carbon materials—I. Unidirectional composites

Unidirectional carbon/carbon composites were developed using high-pressure impregnation/carbonization technique with PAN and pitch based carbon fibers of varying microstructure as reinforcements and different types of pitches as matrix precursors. The composites have been given final heat treatment to 2500-2700 °C. Microstructure of these composites has been evaluated using scanning electron microscope and polarized light optical microscope. Thermophysical properties, i.e., thermal conductivity, coefficient of thermal expansion and specific heat have been evaluated. It is found that the type of fibers and matrix present in the composites influences the absorption (specific heat) and transmission (conductivity) of thermal energy. The temperature dependence of thermal diffusion, specific heat, thermal conductivity and coefficient of thermal expansion has been studied and correlated with microstructure of carbon/carbon composites.     

Influence of matrix and interface on the mechanical properties of unidirectional carbon/carbon composites

The mechanical properties and microstructure of unidirectional carbon/carbon (UD C/C) were investigated. The strength of one type of UD C/C, produced with an intermediate modulus fibre treated to four different levels of an oxidative surface treatment, was determined after each step of the production cycle (of loose, impregnated and carbonized impregnated fibre bundles). The impregnated bundle had a strength 1.9–4.3 times the strength of the loose bundle, whereas after carbonization the strength of the bundle dropped below the strength of the loose bundle. It is suggested that this is mainly caused by the formation of defects in the fibres due to the shrinkage process during carbonization. These defects are larger if a good fibre/matrix bond strength in the green material exists. The possibility that the low strength of carbon/carbon could be caused by stress-concentration effects was excluded with the aid of TEM investigations. They showed that the carbon matrix mainly consisted of vitreous carbon, the modulus of which (E = 35 GPa) does not become effective due to micro- and macrocracks.     

The influence of carbon fibre surface treatment on the mechanical properties of carbon/carbon composites

The influence of carbon fibre type and carbon fibre surface treatment on the mechanical properties of phenolic-based, unidirectionally reinforced carbon/carbon composites has been investigated.It was found that only the reinforcement of carbon/carbon composites with untreated type I fibres results in best mechanical properties. Surprisingly in that case also an optimised surface treatment of the fibres improve the yield of fibre strength. The experimental results have shown that the applicability of the rule of mixtures for the precalculation of the strength of carbon/carbon composites is limited and that the fracture behaviour is controlled by the amount of adhesion between carbon fibres and carbon matrix.     

Probing the carbon nanotube-surfactant interaction for the preparation of composites

Adsorption isotherms of four different surfactants, sodium dodecyl sulfate (SDS), sodium dodecyl benzyl sulfonate, benzethonium chloride and Triton X-100 were measured on multi-wall carbon nanotubes (MWCNT) in water. With the surfactant SDS, the isotherms were also measured on single-wall carbon nanotubes (SWCNT) as well as on MWCNT under various ionic strength and temperature conditions. The nature of the polar head had only little influence on adsorption which was mainly driven by hydrophobic interactions. However, the outcome of the dispersion experiment was dependent on the purity of the carbon nanotubes. Using these results, it was possible to prepare concentrated colloidaly stable dispersions of MWCNTs in water (c = 32 g/L). Conducting MWCNT/polymer composite films could then readily be prepared by simple formulation of the MWCNTs with a polymeric dispersion.     

炼焦煤中灰分对焦炭热性能的影响

研究了炼焦煤的灰分和催化指数,通过小焦炉实验进行了焦炭的反应性和反应后强度的测定。结果表明,灰分催化指数对焦炭的反应性和反应后强度的影响显著。焦炭的反应性与灰分碱性催化指数呈正线性相关,焦炭的反应后强度与灰分碱性催化指数呈负线性相关。     

煤沥青制备针状焦的研究

通过溶剂-离心法净化原料沥青,应用延迟焦化工艺制备针状焦,考察了在聚合过程中QI含量、温度、压力以及时间对成焦的影响.结果表明,原料中QI含量的减少有利于针状结构的生成,当QI含量小于0.1％时能形成大面积的针状结构;适当的温度和压力能使体系的黏度降低,促进气流拉焦作用,在470℃、0.35 MPa条件下得到的针状焦较为理想;充足的反应时间保证小球的充分融并,反应24h体系能融并、重排,形成良好的针状结构.     

Influence of the quinoline-insoluble matter in pitch on carbonization behaviour and structure of pitch coke

The influence of the quinoline-insoluble matter in pitch on the carbonization behaviour and especially on the pitch-coke properties is of basic interest both for the production of pitch coke and the manufacture of carbon electrodes. A more isotropic coke is produced by increasing the amount of quinoline-insolubles. The coefficient of thermal expansion (CTE) by volume measured directly at the coke particle is strongly influenced by the type of quinoline-insoluble. A larger amount of the primary type of quinoline-insolubles causes a large increase of the CTE (volume) from 3.2 to 17.4 × 10^?6K^?1, whereas the secondary type influences the CTE only slightly. This strong influence of quinoline-insolubles on the structure of pitch-binder coke results in a remarkable increase of mechanical strength of carbon artefacts.     

Crystallization and fiber/matrix interaction during the molding of PEEK/carbon composites

The objective of this work was to investigate the effects of molding conditions (molding temperature, residence time at melt temperature, and cooling rate) on the crystallization behavior and the fiber/matrix interaction in PEEK/carbon composites made from both prepreg and commingled forms. In order to investigate the crystallization behavior of the PEEK matrix, the molding process was simulated by differential scanning calorimetric analysis, DSC. The results show that the prepreg and commingled systems do not have the same matrix morphology; prepreg tape was found to be at its maximum of crystallinity, whereas the commingled system was found to be only partially crystalline. The results show that processing must be carried out at a temperature sufficiently high to destroy the previous thermal history of the PEEK matrix; this is an essential requirement to produce efficient fiber/matrix adhesion in the commingled fabric system. Optical microscopic observations also suggest that matrix morphology near the fibers is dependent on the melting conditions; a well-defined transcrystalline structure at the interface is observed only when the melt temperature is sufficiently high. However, the high temperature of molding can easily result in degradation of the PEEK matrix such as chain scission and crosslinking reactions. Thermal degradation of the matrix during processing is found to affect the crystallization behavior of the composites, the fiber/matrix adhesion, and the matrix properties. This effect is more important in the case of a commingled system containing sized carbon fibers because the sizing agent decomposes in the molding temperature range of PEEK/carbon composites. This produces a decrease of the matrix crystallinity and an elimination of the nucleating ability of the carbon fibers. A transition between cohesive and adhesive fracture is observed when the cooling rate increases from 30°C/min to 71°C/min for the composite made from the commingled fabric. This critical cooling rate is found to closely correspond to a change in the mechanism of crystallization of the PEEK matrix.     

The influence of post‐cure on properties of carbon/phenolic resin cured composites and their final carbon/carbon composites

Two‐dimensional (2D) carbon/carbon (C/C) composites were prepared with phenol‐formaldehyde resin and graphite fabric. After curing, polymer composites were post‐cured in air at 160°C and 230°C for several hours and then all polymer composites were carbonized up to 1500°C. The effect of post‐cure on the microstructure and fracture behavior of the resultant carbon/carbon composites was studied. The post‐cure process was characterized by weight loss. This process promoted the crosslinking and condensation reactions and led to the formation of long‐chain, cross‐linked polymeric structures in the matrix. The post‐cured composites had a greater density than the unpost‐cured composite. This study indicates that a longer post‐curing time and higher post‐curing temperature would limit the shrinkage for the post‐cured composites during carbonization. The improvement in linear shrinkage was 22% to 44%. This process also limited the formation of open pores and decreased the weight loss of the resultant C/C composites. The resultant C/C composites developed from post‐cured composites had a greater flexural strength by 7 to 26% over that developed from unpost‐cured composite.     

煅后石油焦热物理性能研究

利用高温导热系数测试仪、TGA/DSC1同步热分析仪研究了煅后石油焦的导热系数、比热容等热物理性能。结果表明:随着温度的升高,煅后石油焦的导热系数和比热容均升高,当温度超过200℃时,导热系数和比热容均出现异常变化,煅后石油焦的氧化起始点为200℃;对导热系数实验数据进行了回归分析,得到了煅后石油焦的导热系数实验关联方程。     

改性煤沥青炭化产物结构和性能

利用化学活性物质对煤沥青进行改性处理，研究了改性煤沥青炭化产物的结构和性能。研究结果表明，改性煤沥青炭化产物的显微结构根据化学活性物质的添加量的不同可是流动状、细镶嵌状和光学各向异性结构；适量的添加化学活性物质，可得到微晶发育良好，抗氧化性优良的沥青炭化产物。     

Grafting straight carbon nanotubes radially onto carbon fibers and their effect on the mechanical properties of carbon/carbon composites

Straight carbon nanotubes (CNTs) were grafted radially onto carbon fibers to produce hybrid materials that were used to reinforce carbon/carbon (C/C) composites. Mechanical property tests indicated that these C/C composites have improvements in out-of-plane and in-plane compressive strengths and interlaminar shear strength of 275%, 138% and 206%, respectively. They also have a large decrease in the anisotropy of mechanical properties, compared with pure C/C composites. This great improvement is the result of the simultaneous reinforcements to the fiber/matrix interface and the matrix provided by the grafted CNTs.