Properties of silicon-containing carbon fiber materials prepared using cellulose

Silicon-containing carbon fiber sorbents, which exhibited sufficiently high sorption activity and increased stability to the action of oxygen at high temperatures, as compared with that of an analogous material based on individual cellulose, were prepared by the carbonization and the subsequent activation of cellulose compositions with polycarbosilane.     

Enhancing the thermal stability of S/Se based thermoelectric materials using self-generated oxide films

This study focuses on the thermal stability of Cu_1.8S materials. During the ball milling process, metal powder is added to the milled Cu_1.8S powder, and then the obtained powder is sintered using current assisted sintering to obtain dense blocks. The aim is to enable the added metal elements to spontaneously grow an oxide film on the surface of the material block at high temperature, achieving protection of the material matrix. The thermal stability of materials is evaluated by utilizing changes in room temperature phase composition before and after high-temperature heat treatment, changes in material electrical conductivity during high-temperature processes, and cyclic electrical transmission performance testing. By observing the surface oxide film state of the material after high-temperature treatment, the commonalities and differences in the effects of different element additions on the thermal stability of the material were analyzed. The effects of different metal elements on material hardness and electrical transmission performance were evaluated. It is found that adding metal powder can effectively improve the thermal stability of Cu_1.8S, improve material hardness, and regulate the electrical transmission performance of the material. The characteristics of the oxide film formed by the spontaneous growth of metal elements and oxygen on the surface of the material substrate determine the effectiveness of the oxide film in protecting the material from high temperatures. The pure Cu_1.8S bulk can only maintain stability at 300 ^oC, and the addition of Cr, Al, 316L, Fe, and Mn powder respectively increased the stable temperature of the material to 400, 400, 450, 450, 500 ^oC. Adding metal elements to the material matrix to grow an oxide film on the surface of the material to prevent high-temperature oxidation or decomposition is an effective way to improve the thermal stability of S/Se compounds.     

我国间位芳纶高纯原料生产工艺现状及建议

阐述了我国间苯二甲酰氯和间苯二胺两种间位芳纶主要原料的生产工艺现状,概括了其相应工艺的优缺点。指出目前这两种原料发展中所面临的主要问题和不足,主要是间苯二胺存在产业链配套不完善、生产工艺不成熟、环境污染等问题。并提出必须尽快培育出3~5家技术一流、产业链配套完善和环保设施齐全的间位芳纶原料企业,确保我国间位芳纶原料供应安全的建议。     

Increasing the thermoelectric power factor of polymer composites using a semiconducting stabilizer for carbon nanotubes

Poly(vinyl acetate) (PVAc) copolymer latex-based composites were prepared with multi-walled carbon nanotubes (MWCNT), stabilized with sodium deoxycholate (DOC) or meso-tetra(4-carboxyphenyl) porphine (TCPP). SEM images show that a segregated MWCNT network developed during drying, which resulted in relatively low percolation thresholds (1.62 and 2.17 wt.% MWCNT for DOC and TCPP, respectively). The electrical conductivity (σ) of TCPP-stabilized composites is very similar to that of DOC-stabilized, while the thermopower (or Seebeck coefficient (S)) is five times as large. This enhanced thermopower suggests the MWCNT:TCPP/PVAc composite will have an order of magnitude greater power factor (S²σ), which is an important measure of efficiency for thermoelectric materials (i.e., materials capable of converting a thermal gradient to a voltage). The thermal conductivity of these composites remains comparable to typical polymeric materials due to numerous tube–tube connections that act as phonon scattering centers. The universality of this approach was confirmed using much more electrically conductive double-walled carbon nanotube-filled composites that showed similar improvement with TCPP stabilization. It is possible that other porphyrin derivatives, or semiconducting molecules capable of stabilizing nanotubes in water, could be used to further enhance the Seebeck coefficient and improve the ability of these composites to convert waste heat into electricity.     

A possibility of the production of carbon nanotubes from heavy hydrocarbons

A possibility of the production of carbon nanotubes from heavy hydrocarbon resources derived from natural asphalt was examined. Before the use of heavy hydrocarbons, pure compound, toluene was used as the pure substrate to establish the reaction system for the production of carbon nanotubes. Carbon nanotubes were found in the carbonaceous product deposited on inner wall of a quartz tube and at the exit of the tube. The carbonaceous product was observed by scanning electron microscopy and analyzed by temperature-programmed oxidation experiments to identify the presence of carbon nanotubes. Based on the reaction system and reaction conditions with toluene, the production of nanotubes was examined by using heavy hydrocarbons such as asphaltene and maltene fractions from a natural asphalt. Under selected reaction conditions including the reaction temperature and the amount of the catalyst, carbon nanotubes with a diameter of 30–60 nm were found.     

Catalytic systems based on carbon fiber materials for the low-temperature oxidation of carbon monoxide

New heterogenized catalytic systems for the low-temperature oxidation of CO were synthesized by supporting solutions of Pd, Cu, and Fe salts on carbon fibrous materials (carbopon and busofit). The carbon supports were studied by elemental analysis, SEM, TGA, and TPD. The effects of the nature of the support, the concentration and composition of the active component, and the conditions of preparation on the efficiency of the catalytic system were studied. It was ascertained that attenuation of hydrophilic properties of the support led to the decrease in system activity. The investigation of the catalysts by XPS showed that sample treatment in the reaction medium results in redistribution of the components of the active phase in the near-surface layer of the catalyst. The catalytic system based on carbon fibrous material carbopon prepared by supporting active components (Pd, Cu, and Fe salts) in three stages with intermediate activation in the reaction medium ensures 95% conversion of CO under respiratory conditions, and is promising for the design of the main element of breathing masks on its basis.     

Increase in the refractoriness of carbon composite materials with use of heat-resistant ceramic coatings

The main directions are considered for increasing the refractoriness of structural graphite materials, carbon-carbon composite materials (CCCM), and structures made of them. Practical examples are proposed for increasing the refractoriness of materials based on carbon in the application temperature range from 1200 to 1700°C. Results are provided for experimental study of four types of increased refractoriness. It is demonstrated that the contemporary direction of domestic work for increasing the refractoriness of structural graphite materials and CCCM agrees on the whole with a series of overseas achievements in this field. Translated from Novye Ogneupory, No. 7, pp. 50–55, July 2008.     

Study of the possibility of using carbon composites in the creation of industrial fans applied to refractory production

An industrial fan impeller is tested, its strength reliability is established, and the calculated operating time is determined for a carbon composite in an air atmosphere and flue gases. Results of tests confirm the high corrosion resistance of carbon material in corrosive liquid media associated with the production of refractory materials.     

Modification of the carbon fiber surface with a copper coating for composite materials with epoxy

Surface treatment of carbon fibers is essential to provide adequate interfacial interaction, and strength in carbon fiber/epoxy composites. The electrodeposition of a metallic copper coating on the carbon fiber surface has been examined as an alternative method to improve carbon fiber-epoxy interfacial properties. The wettability of the carbon fiber by the epoxy resin was improved as a result of copper electrodeposition. As a consequence, the adhesion between the carbon fiber and epoxy was also greatly improved by the surface electrolytic treatment used. The electrodeposition conditions affected significantly both wettability and adhesion phenomena. The electrolytic current had a strong effect on the interface performance. It was found that there was an intermediate electrolytic current, within the range used, which promoted better wetting and composite strength, compared with conventionally surface-oxidized carbon fibers.     

The production of carbon materials by hydrothermal carbonization of cellulose

Highly functionalized carbonaceous materials were produced by means of the hydrothermal carbonization of cellulose at temperatures in the 220-250 °C range. The formation of this material follows essentially the path of a dehydration process, similar to that previously observed for the hydrothermal transformation of saccharides such as glucose, sucrose or starch. The materials so formed are composed of agglomerates of carbonaceous microspheres (size ∼2-5 μm), as evidenced by SEM. The combination of the results of the elemental analysis with that obtained by different spectroscopic techniques (infrared and Raman spectroscopy, and XPS) has allowed us to inferred that, from a chemical point of view, the solid product consists of small clusters of condensed benzene rings that form stable groups with oxygen in the core (i.e. ether, quinone, pyrone), whereas the shell possesses more reactive/hydrophilic oxygen functionalities (i.e. hydroxyl, carbonyl, carboxylic, ester).     

碳纤维生产废气焚烧法处理工艺探讨

采用焚烧炉直接焚烧法处理碳纤维生产中的炭化废气,探讨了柴油流量、柴油压力、炉膛压力等工艺条件对焚烧炉运行状况及处理效果的影响。结果表明:在柴油流量大于12.5 L/h、柴油压力大于0.4MPa、炉膛压力-1 200~-600 Pa条件下,焚烧炉可以连续稳定运行;炭化废气经焚烧炉连续稳定处理后,碳纤维生产废气中氰化氢去除率达98%以上,达到《GB16297—1996大气污染物综合排放标准》要求。     

Effect of moisture on the thermoelectric properties in expanded graphite/carbon fiber cement composites

A kind of dry mixing and pressing process was introduced to prepare expanded graphite/carbon fiber cement composites (EG-CFRC). Significant effect of moisture on the thermoelectric properties of EG-CFRC was observed. The higher the moisture content is, the greater the absolute Seebeck coefficient. The maximum of absolute Seebeck coefficient 11.59 μV/°C was obtained with moisture of 14.98% at 33 °C. Simultaneously, the maximum of electrical conductivity 0.78 S cm⁻¹ was got with moisture of 11.44%. Furthermore, the largest power factor 7.85×10⁻⁴ µW m⁻¹ K⁻² was calculated at 33 °C with moisture of 11.44%. The carrier scattering, polarization effects and high density defects interface of EG-CFRC are attributed to the enhancement of thermoelectric properties in the case of higher moisture content.     

关于碳纤维及其复合材料测试方法的标准化

论述了国内外碳纤维及其织物、预浸料、复合材料的测试方法及标准化,供国内有关测试单位及专业技术人员参考。     

NMR a critical tool to study the production of carbon fiber from lignin

The structural changes occurring to hardwood Alcell™ lignin as a result of fiber devolatilization/extrusion, oxidative thermo-stabilization and carbonization are investigated in this study by solid-state and solution nuclear magnetic resonance (NMR) spectroscopy techniques. Solution based ¹H–¹³C correlation NMR of the un-spun Alcell™ lignin powder and extruded lignin fiber detected modest changes occurring due to fiber devolatilization/extrusion in the type and proportion of aliphatic side-chain carbons or monolignol inter-unit linkages. Molecular weight analysis by gel permeation chromatography (GPC), along with an additional ³¹P NMR method used to indicate changes in terminal hydroxyl functionality, suggest fiber devolatilization/extrusion causes both chain scission and condensation reactions. ¹H CRAMPS (combined rotation and multiple-pulse spectroscopy) and ¹³C cross-polarization/magic angle spinning (CP/MAS) spectra of extruded and stabilized lignin fibers indicate stabilization severely reduces the proportion of methoxy groups present, while also increasing the relative proportion of carbonyl and carboxyl-related structures, typically associated with cross-linking chemistries. ¹³C direct-polarization/magic angle spinning (DP/MAS) analysis of stabilized and carbonized fibers shows an increased relative amount of carbon–carbon bonds on aryl structures and a relative decrease of aryl ethers. DP/MAS dipolar dephasing experiments suggest that a majority of non-protonated carbons convert from carbonyl to aryl and condensed aryl structures during carbonization.     

The pull-out and failure of a fiber bundle in a carbon fiber reinforced carbon matrix composite

The interfacial failure is examined for a unidirectionally reinforced carbon fiber/carbon matrix composite. A novel tensile test is conducted which realizes the processes of interfacial debonding and subsequent pull-out of a fiber bundle from the surrounding composite medium. The critical stress at the onset of delamination cracking is related to the fracture energy (the critical energy release rate for mode II cracking). A force-balance equation of a fiber bundle, which is quasi-statically pulled-out of the composite socket, is formulated in terms of the inter- and intra-laminar shear strengths of the composite. This equation is successfully used to estimate the delamination crack length along the debonded fiber bundle, as a function of the stress applied to the bundle.