共查询到20条相似文献,搜索用时 31 毫秒
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《Fuel》2003,82(15-17):2045-2049
Carbon molecular sieves (CMS) are valuable materials for the separation and purification of gas mixtures. In this work, plasma deposition was used aiming to the formation of pore constrictions, by narrowing the surface pore system of commercial activated carbon fibers (ACF). For this reason propylene/nitrogen or ethylene/nitrogen discharges of 80 and 120 W were used. The molecular sieving properties of the plasma treated ACF were evaluated by measuring the adsorption of CO2 and CH4. The CO2/CH4 selectivity was significantly improved and depended on plasma treatment conditions (discharge gas and power). The optimum CO2/CH4 selectivity (26) was observed for C2H4/N2 plasma treated ACF at 80 W. Sample scanning electron microscopy (SEM) analysis after plasma treatment revealed an external film formation and X-ray photoelectron spectroscopy (XPS) analysis showed the incorporation of nitrogen functional groups in the film, which probably interact with CO2, thereby altering CO2/CH4 selectivity. 相似文献
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Teresa Gumula Jerzy Michalowski Marta Blazewicz Stanislaw Blazewicz 《Ceramics International》2010,36(2):749-753
Porous multidirectional carbon/carbon composite obtained by pulse chemical vapour infiltration (PCVI) was impregnated with silicon carbide (SiC) derived from pyrolysis of polymethylsiloxane resin (PMS). The impregnation process was made to improve oxidation resistance and mechanical properties of MD C/C composite. The resin was used as a source of silicon carbide component of the composite forming after heat treatment above 1000 °C. During this process SiC thin filaments were formed inside the porous carbon phase. The aim of this work was to investigate the structure and microstructure of the constituents of carbon composite obtained after pyrolysis of SiC PMS precursor. Microscopic observations revealed that during careful heat treatment of crosslinked polymethylsiloxane resin up to 1700 °C, the filaments (diameter 200–400 nm) crystallized within porous carbon phase. The filaments were randomly oriented on the composite surface and inside the pores. FTIR spectra and XRD analysis of the modified C/C composite showed that filaments had silicon carbide structure with the crystallite size of silicon carbide phase of about 45 nm. The Raman spectra revealed that the composite contains two carbon components distinctly differing in their structural order, and SiC filaments present nanocrystalline structure. 相似文献
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《Diamond and Related Materials》1999,8(8-9):1659-1676
Hydrogen free diamond-like carbon (DLC) films have been the subject of investigation all over the world during the past 25 years due to the unique combination of their properties that can be found between those of diamond and those of graphite. Intensive work throughout the world in the past 10 years has led to a much better understanding of the complicated mechanisms involved in the deposition of these films. This led to a significant improvement in the deposition processes in the variety of systems employed, enabling fabrication of films with better properties. The present work gives the author's assessment of the current status of DLC film deposition. Topics addressed include: deposition systems; characterization methods; film properties; and possible applications. 相似文献
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《Ceramics International》2015,41(6):7677-7686
Ablation behavior of ZrB2–SiC protective coating for carbon/carbon composites during oxyacetylene flame test at 2500 °C was investigated by analyzing the microstructure differentiation caused by the increasing intensity of ablation from the border to the center of the surface. After ablation, a continuous SiO2 scale, a porous SiO2 layer inlaid with fine ZrO2 nuclei, and a continuous ZrO2 scale respectively emerged in the border region, the transitional region, and the center region. In order to investigate the ablation microstructure in the initial stage, the sub-layer microstructure was characterized and found to be mainly formed by coral-like structures of ZrO2, which showed huge difference with the continuous structure of ZrO2 on the surface layer. A kinetic model concerning the thickness change induced by volatilization and oxidation during ablation was built to explain the different growth mechanisms of the continuous ZrO2 scale and the coral-like ZrO2 structure. 相似文献
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《Carbon》2013
An asymmetric supercapacitor with high energy and power densities has been fabricated using MnO2/carbon nanofiber composites as positive electrode and activated carbon nanofibers as negative electrode in Na2SO4 aqueous electrolyte. Both electrode materials are freestanding in nature without any conductive additives or binders and exhibit outstanding electrochemical performances. The as-assembled asymmetric supercapacitor with optimal mass ratio can be operated reversibly over a wide voltage range of 0–2.0 V, and presents a maximum energy density of 30.6 Wh kg−1, which is much higher than those of symmetric supercapacitors. Moreover, the supercapacitor exhibits excellent rate capability (high power density of 20.8 kW kg−1 at 8.7 Wh kg−1) and long-term cycling stability with only 6% loss of its initial capacitance after 5000 cycles. These attractive results make these freestanding materials promising for applications in aqueous electrolyte-based asymmetric supercapacitors with high energy and power densities delivery. 相似文献
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As the booming wind energy industry turns to bigger, more powerful turbines, blade manufacturers must develop the composite materials and processing technology to keep pace. George Marsh reports. 相似文献
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《Fuel Processing Technology》2002,79(3):239-244
During granular carbon–carbon composites manufacturing, the binder (a pitch) is carbonized while surrounded by solid filler particles. This geometrical limitation imposed on the carbonization medium results in constraints responsible for textural modifications of the pitch-based coke. We studied the consequences of geometrical limitation on pitch carbonization, and also the influence of the as-formed composites multiscale organization on their mechanical properties and carboxyreactivity behavior. The micrometer scale is relevant to understand composite reactivity while the submillimeter scale enables a better comprehension of the mechanical properties. 相似文献
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To improve the oxidation protective ability of carbon/carbon composites, ZrB2–SiC gradient coating was prepared on the surface of C/C composites by an in-situ reaction method. The ZrB2–SiC gradient coating consisted of an inner ZrB2–SiC layer and an outer ZrB2–SiC–Si coating. The phase composition and microstructures of the multiphase coating were characterized by XRD, EDS and SEM. Results showed that the inner coating is mainly composed of ZrB2 and SiC, while the outer multiphase coating is composed of ZrB2, SiC and Si. The multilayer coating is about 200 μm in thickness, which has no penetration crack or big hole. The oxidation behavior of the coated C/C composites at 1773 K in air was investigated. Results show that the gradient ZrB2–SiC oxidation protective coating could protect C/C from oxidation for 207 h with only (4.56±1.2)×10−3 g/cm2 weight loss, owing to the compound silicate glass layer with the existence of thermally stable phase ZrSiO4. 相似文献
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In order to improve the oxidation resistance of C/C composites, a ZrB2–SiC/SiC oxidation protective dual-layer coating was prepared by a pack cementation combined with the slurry paste method. The phase and microstructure of the coating were characterised by X-ray diffraction, scanning electron microscope and energy-dispersive spectrometer analyses. The anti-oxidation and thermal shock resistance of the coating were also investigated. It was found that the ZrB2–SiC/SiC coating could effectively improve the oxidation resistance of the C/C composites. The weight loss of the coated samples was only 1.8% after oxidation at 1773?K for 18?h in air. The coating endured 20 thermal shock cycles between 1773?K and room temperature with only 4.6% weight loss. 相似文献
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《Ceramics International》2020,46(13):21233-21242
In this study, high-temperature oxidations and indentations on silicon carbide (SiC)- and hafnium carbide (HfC)-coated carbon–carbon (C/C) composites were investigated to prevent the oxidation of C/C composites in air. The SiC and HfC layers were coated to protect the composite from oxidizing in air at a high temperature. High-temperature oxidation tests were performed at 500 °C, 1,000 °C, 1,350 °C, and 1,500 °C for 1 h in air and then cooled to room temperature by thermal shock. This cycle was repeated until the coating layer was damaged. As a result of measuring the weight change according to the thermal cycle and observing the fiber damage in the C/C composites, the oxidation resistance of HfC was evaluated to be superior to that of SiC. The change of the mechanical behavior was investigated using an indentation test with a tungsten carbide ball with a radius of either 3.18 or 7.93 mm before and after the high-temperature oxidation test by thermal shock. The relative elastic modulus was predicted based on the slope of the indentation load–displacement curve during loading or that of the curve during unloading. The relative hardness was also analyzed based on residual displacement after indentation. The hardness and elastic modulus of the HfC and SiC coating were higher than those of C/C composites and the mechanical properties of the HfC-coated C/C composite were relatively good compared with those of the SiC-coated composites prior to the thermal shock test. In particular, in this study, it was found that the mechanical behaviors of HfC-coated C/C composites exposed to temperatures >1,000 °C in air were transferred from elastic to quasi-plastic. The quasi-plasticity of the HfC coating layer was evaluated to be excellent regarding its resistance to mechanical damage as the coating layer was not easily delaminated or damaged even by oxidation. 相似文献
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《Journal of the European Ceramic Society》2000,20(9):1397-1402
Composite samples were obtained from hydroxyapatite powder and carbon fibres by hot pressing at 1100°C and 25 MPa for 15 min in argon atmosphere. Two types of cut carbon fibres produced in a carbonisation process of polyacrylonitrile (PAN) precursor were used both in non-coated or coated form. The coatings of calcium phosphate were applied by sol–gel technique. The highly sintered composite with the best strength properties was obtained from coated carbon fibres with basic character of the surface. The existence of hydroxyl groups on fibre surface makes possible formation of bonds with the calcium phosphate layer formed as a result of polycondensation following the sol–gel procedure. 相似文献
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Carbon nanotubes are demonstrated as a good support for the immobilization of -Glucosidase. This is an enzyme with high molecular weight (ca. 135 kDa). A high enzyme loading of 630 mg per gram of support was achieved in 12 h. The link between the enzyme and the carbon nanotubes surface was by electrostatic interactions due to the different charges of the enzyme and the support at the pH of the immobilization. Immobilized -Glucosidase showed a catalytic activity above 400 U/g on the hydrolysis of 4-nitrophenyl--D-glucopyranoside (p-NPG). 相似文献