共查询到20条相似文献,搜索用时 15 毫秒
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F. MontillaE. Morallón J.L. VázquezJ. Alcañiz-Monge D. Cazorla-Amorós A. Linares-Solano 《Carbon》2002,40(12):2193-2200
Carbon-ceramic composites have been prepared and characterised by different techniques (electron microscopy, X-ray microanalysis, X-ray diffraction and cyclic voltammetry). The effect on the conductivity of the thermal treatment temperature of the composites and the structure of the starting ceramic has been analysed. The results demonstrate that the layered structure of the clay determines their conductivity. The composites prepared are conductors and the conductivity goes through a maximum with increasing thermal treatment. Platinum has been successfully deposited on the carbon-ceramic composite by chemical and electrochemical methods. A better distribution of platinum and smaller particle sizes are obtained by the electrochemical method. The direct electrooxidation of methanol in acid medium has been studied on platinum-modified carbon-ceramic electrodes. 相似文献
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Thermokinetic analysis of three pitch samples was carried out: coal tar pitch obtained from light coke oven tar (P), mesophase pitch after 10.5 h (MP1), and mesophase pitch after 12 h (MP2) thermopreparation at 410 °C. The process was realized in a continuous system with a 10 kg mass being charged to the reactor. It was demonstrated using Kissinger’s law that the temperature criterion, the first-order thermokinetics and the calculated Arrhenius law parameters fulfill the isokinetic effect when the classical routes of thermokinetic analysis of the samples prepared under dynamic conditions (at three heating rates) are used, which makes the qualitative interpretation of differences between these samples difficult. An alternative solution was proposed using the relative rate of thermal decomposition. The temperature ranges of the chemical reactions leading to the formation of mesophase structures, as well as the temperature ranges of the coking processes of the Fixed Carbon phase, were determined. 相似文献
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Analysis and modeling of mesophase sphere generation, growth and coalescence upon heating of a coal tar pitch 总被引:2,自引:0,他引:2
The present study has been undertaken aiming: (1) to provide an experimental procedure for measurement of characteristics of mesophase sphere formation from a coal tar pitch upon heating at 673-723 K in terms of the time-dependent changes in the population density and the radius distribution of the spheres and (2) to prove that the nucleation, growth and coalescence of the spheres are essential for quantitative explanation of the time-dependent changes. In regard to (1), this paper describes the conditions that are required in microscopic analysis of cross-sections of the bulk of heat-treated pitch for the conversion of the population density and the radius distribution of the cross-sectional circles into those of spheres on volume basis. Regarding (2), a model analysis demonstrates that the change in the radius distribution with time, as well as that in the population density of spheres, can quantitatively be predicted. The analysis also reveals that the spheres grow without undergoing coalescence in the early period, and the sphere coalescence commences after termination of sphere generation while the growth continues. 相似文献
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Different oxidation treatment was used for the increase of the softening point of a commercial coal tar pitch. H2SO4, HNO3, H2O2 and air are selected as treatment reagents. These preliminary investigations show that the oxidation treatment of commercial coal tar pitch with different reagents at 160 °C and heat treatment to 250 °C causes considerable changes in the chemical composition of obtained pitches. This leads to increase of TI and QI fraction, and results in considerable increase in the softening point of the pitches. The yield of modified pitches is considerable in the case of treatment with H2SO4, H2O2, and HNO3 and lesser in the case of air blowing. The data obtained also indicate some differences in the composition and softening point of pitches obtained after modification with different reagents. These differences could influence the applicability of the obtained pitches in the various areas of carbon material production. 相似文献
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E. A. Dawson G. M. B. Parkes P. A. Barnes M. J. Chinn L. A. Pears C. J. Hindmarsh 《Carbon》2002,40(15):974-2903
The rate of evolution of CO2 or CO was used to control the low temperature activation of carbon fibres in O2 mixtures via a feedback loop operated by a PC and in-house software. The CO2 or CO concentration was monitored by a mass spectrometer and its level kept constant by varying the O2 concentration using mass flow controllers. Experiments were carried out at the same evolution rates for identical times at temperatures of 500–800 °C. It was found that the rate of carbon burn off was not constant and varied with the temperature, especially where the rate of CO2 evolution was controlled. The proposed reason for this was the high temperature gas phase oxidation of CO. However, surface areas of up to 1500 m2 g−1 were produced by these methods and thermal runaway was avoided. 相似文献
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Modified characteristics of mesophase pitch prepared from coal tar pitch by adding waste polystyrene
The toluene soluble of coal tar pitch was carbonized with waste polystyrene. The properties of mesophase pitches were characterized using polarized light optical microscope, apparent viscometer, FT-IR, 1H NMR and X-ray diffractometer. After adding the waste polystyrene into the toluene soluble of coal tar pitch, the soluble mesophase were was increased from about 9% to 52% and the mesophase pitches were changed from 74% with coarse mosaic texture to 100% with flow domain texture. The mesophase pitches were transformed from thixotropy to unthixotropy. By waste polystyrene added into the toluene soluble of coal tar pitch, the methylene group was increased a lot. The presence of more alkyl groups modified the characteristics of mesophase pitches and improved the assembly of mesophase pitch molecules. 相似文献
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以煤沥青为原料,采用直接热聚合工艺制备出优质中间相沥青。研究了热聚合温度及保温时间对中间相沥青族组成及光学组织结构等性能的影响,并对反应机理进行了深入研究,得到了制备中间相沥青的最佳工艺条件。研究表明,在一定条件下,通过热聚合,在低温、长时间或高温、短时间都能制备优质中间相沥青。在360℃、5 h条件下制备的中间相球晶较小,分布较分散;而在380℃、4 h条件下制备的球晶较大,分布较集中。制备的中间相可作为高级炭材料的优质前躯体,为制取高质量的新型炭材料提供了一条新的途径,对煤炭资源的综合利用具有十分重要的意义。 相似文献
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《Carbon》2002,40(14):2719-2725
The isotropic phase isolated from a thermally treated coal-tar pitch was studied as a possible precursor for carbon fibres. Extraction with different solvents was performed in order to increase its softening point and so enable higher stabilisation temperatures to be used, with a significant reduction in time. The extraction conditions were selected studying the softening temperatures of the residues, the results of their thermogravimetric analysis and reactivity in air studied by means of differential scanning calorimetry. The residue obtained with a mixture of 40% acetone-60% acetonitrile was found to be the most suitable precursor for the fibres. The carbonised fibres showed a homogeneous surface and diameter, and had tensile properties comparable to other isotropic fibres described in the literature. 相似文献
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Fibrous porous materials (FPMs) have been prepared by coating a glass fiber with an aqueous solution of poly(vinyl alcohol) (PVA) and H3PO4, followed by stabilization and heat treatment in air. The H3PO4 was then removed by washing with deionised water and NaOH. The results show that H3PO4 acts as a dehydration agent to promote pyrolytic and thermal crosslinking of PVA at a much lower temperature of 170 °C, leading to FPMs having much higher char yields and surface areas. The activation in air is of benefit to achieve higher surface areas as compared to using N2. Utilizing a fiberglass mat to support coatings of PVA activated with H3PO4 results in much higher specific surface areas. The activation temperature, activation time and concentration of H3PO4 have strong effects on the surface area, pore size distribution and coating content of FPMs. 相似文献
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A new approach is provided to resolve the large-scale applications of coal tar pitch. Carbon foams with uniform pore size are prepared at the foaming pressure of normal pressure using coal tar pitch as raw materials. The physical and chemical performance of high softening point pitch(HSPP) can be regulated by vacuumizing owing to the cooperation of vacuumizing and polycondensation. Results indicate that the optimum softening point and weight ratio of quinoline insoluble are about 292℃ and 65.7%, respectively. And the optimum viscosity of HSPP during the foaming process is distributed in the range of 1000-10000 Pa·s. The resultant carbon foam exhibits excellent performance, such as uniform pore structure, high compressive strength(4.7 MPa), low thermal conductivity(0.07 W·m~(-1) ·K~(-1)), specially, it cannot be fired under the high temperature of 1200 ℃.Thus, this kind of carbon foam is a potential candidate for thermal insulation material applied in energy saving building. 相似文献
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Thanh X. Nguyen 《Carbon》2005,43(4):775-785
In this paper, we present results of the internal structure (pore size and pore wall thickness distributions) of a series of activated carbon fibers with different degrees of burn-off, determined from interpretation of argon adsorption data at 87 K using infinite and finite wall thickness models. The latter approach has recently been developed in our laboratory. The results show that while the low bun-off samples have nearly uniform pore size (<0.6 nm), the pore size distribution of the high burn-off samples becomes broader, with a significant increase in proportion of larger pores. The results of pore wall thickness distribution are generally consistent with development of porosity with increasing degree of burn-off. Further they show good correspondence with X-ray diffraction. 相似文献
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《Ceramics International》2020,46(17):27232-27237
SiC-SiOx nanowires (NWs) with core-shell and chain-bead structures were synthesized via a catalyst-free chemical vapor deposition (CVD) route without Ar gas, using silicon and coal tar pitch powders as raw materials. The SiC-SiOx NWs with sharp tips formed by solid-vapor between Si (s) and CO (g) or C (s) and SiO (g), liquid-vapor between Si (l) and CO (g), and vapor-vapor between SiO (g) and CO (g) growth process along the [111] direction. The NWs were several millimeters in length, and the average diameters of the chains and beads were 40–90 nm and 325 nm, respectively. The obtained NWs had good blue-green photoluminescence property owing to the stacking faults and amorphous SiOx. This novel CVD route is simple, low cost and suitable for large-scale production. 相似文献
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A study of the characteristics of activated carbons produced by steam and carbon dioxide activation of waste tyre rubber 总被引:3,自引:0,他引:3
Guillermo San Miguel 《Carbon》2003,41(5):1009-1016
This paper presents a study into the effect of different activation conditions on the porosity and adsorption characteristics of carbon adsorbents produced from waste tyre rubber. For the purpose of this work, three carbon series were produced using different activation temperatures (between 925 and 1100 °C) and oxidising agents (steam or carbon dioxide). Carbons produced to different degrees of burn off were characterised using gas (nitrogen) and liquid phase (phenol, methylene blue and Procion Red H-E2B) adsorption. Total micropore volumes and BET surface areas increased almost linearly with the degree of activation to 0.554 ml/g and 1070 m2/g, respectively, while the development of external surface area was particularly rapid at degrees of activation above 50 wt% burn off. Steam was observed to generate a narrower but more extensive microporosity than carbon dioxide. However, carbon dioxide produced carbons of slightly larger external surface areas. Activation at higher temperatures resulted in pores of slightly larger dimensions, although this was only evident in highly activated samples. Porosity characteristics were reflected in the capacity of the carbons to adsorb species of different molecular size from solution. In this respect, steam-activated carbons presented greater capacities for the adsorption of smaller molecular size compounds (phenol), while carbon dioxide-activated carbons adsorbed larger textile dyes more effectively. 相似文献