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2015, 30(2): .

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Advances in the ablation resistance of C/C composites

FU Qian-gang, ZHANG Jia-ping, LI He-jun

2015, 30(2): 97-105.

Abstract(1596)

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Carbon/carbon (C/C) composites are considered the most promising materials for high-temperature structural applications owing to their excellent properties at high temperature. However, oxidation and ablation limits their applications in oxygen-containing environments at ultrahigh temperatures and high-speed gas flows. How to improve oxidation and ablation resistance of the C/C composites has become a critical issue. The methods for improving oxidation and ablation resistance of the C/C composites are reviewed, which mainly focus on optimizing the carbon fiber weave structure, controlling the pyrolytic carbon texture, modifying the matrix, and coating with anti-ablative ceramic layers. Matrix modification and coating technology have been proved to be the two effective ways of dealing with the problem. Development directions on producing oxidation and ablation resistive C/C composites are concentrated on decreasing preparation cost, controlling pyrolytic carbon texture, optimizing compositions of the doped ceramics used in the matrix and the coating layer, and combining matrix modification with an anti-ablation coating.

A review of carbon-carbon composites for engineering applications

SU Jun-ming, ZHOU Shao-jian, LI Rui-zhen, XIAO Zhi-chao, CUI Hong

2015, 30(2): 106-114.

Abstract(1839)

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Five kinds of carbon-carbon composites used in aerospace, aircraft, photovoltaics, powder metallurgy and high temperature furnaces are reviewed, whose preforms were fabricated by needle piercing, orthogonal three-direction weaving, radial weaving, axial weaving and puncture. The physical, mechanical, thermal, ablation, and wear properties and service life were compared with corresponding materials from overseas manufacturers. Correlations between the performance, type of preform and carbon matrix, and interfacial bonding state was obtained. These analyses and comparisons can lay a foundation for the construction of a database-sharing platform for C/C composites in engineering applications. Research efforts need to be focused on the fine structure and gradient design of preforms and the optimum combination of different carbon matrices for the improvement of C/C composites.

Preparation and characterization of a polyimide coating on the surface of carbon fibers

YUAN Hao-jie, LU Chun-xiang, ZHANG Shou-chun, Wu Gang-ping

2015, 30(2): 115-121. doi: 10.1016/S1872-5805(15)60179-2

Abstract(1057)

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Organic, solvent-free polyamic acid sizing was coated onto T300 grade carbon fibers (3k) to prepare a polyimide (PI) coating having a high thermal stability and oxidative resistance. The surface of PI-coated carbon fibers was characterized by FTIR and SEM. The mechanical strength of the carbon fibers, thermal stability and oxidative resistance of the coating were also investigated. Results indicate that a continuous and uniform PI coating is formed on the surface of the carbon fibers. Compared to a carbon fiber coating with epoxy, the PI coating produces excellent thermal stability with onset decomposition and a 5% weight-loss temperatures of 567 and 619 ℃, respectively. The tensile strength of PI-coated carbon fibers after thermal oxidation in air at 400 ℃ for 1 h has only a slight decrease of 6%, which is significantly lower than the decrease of 22% for epoxy-coated fibers.

Effect of boron-catalyzed graphitization on the mechanical properties and microstructure of carbon fibers

WANG Hui-qi, GUO Quan-gui, LIU Zhan-jun, HAN Tao, FENG Zhi-hai, LIU Lang

2015, 30(2): 122-127.

Abstract(804)

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Boron-catalyzed graphitization of carbon fibers was conducted in a boron-doped graphite crucible at 2 000 ℃, in which boron diffused from the crucible to the carbon fibers to act as the catalyst. The microstructures, boron contents and mechanical properties of the resulting carbon fibers were characterized by Raman spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy and mechanical tests. Results indicate that boron has a significant impact on the fiber microstructure. Raman spectra indicate the presence of distortions in the graphitic layers. The tensile modulus of boron-doped carbon fibers obviously increases with boron content and the tensile strength is also higher than that of the original carbon fibers at boron concentrations between 0.58 to 0.68 at.%.

A graphene/carbon black hybrid material: a novel binary conductive additive for lithium-ion batteries

LI Yong, LU Xiao-hui, SU Fang-yuan, HE Yan-bing, LI Bao-hua, YANG Quan-hong, KANG Fei-yu

2015, 30(2): 128-132.

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A novel graphene(GN)/carbon black(CB) binary conductive additive has been developed, which is characterized by a unique microstructure and excellent performance for lithium ion batteries (LIBs). It was fabricated using a hydrothermal process, followed by heat treatment. The introduction of CB particles prevents GN from agglomerating and hence improves the electronic conductivity of the resulting additive. CB particles can also enhance the Li⁺ ion diffusion, owing to a reduction of the GN fraction and an increase in electrolyte adsorption. Therefore, the rate performance of the LIB is improved to some extent. Experimental data shows that the specific capacity of LiFePO₄ containing 5% of this binary conductive additive (after 900 ℃ treatment) is 73 mAh/g at 10 C, which is superior to that of LiFePO₄ with 10% of CB (62 mAh/g). Compared with the latter, the former has a specific capacity increase of 25% based on the mass of the whole electrode and shows superior cycle stability.

Structure and optical property of functionalized reduced graphene oxides as electron acceptors in polymer solar cells

QU La-qin, YANG Wei-jia, HAO Ya-min, YANG Yong-zhen, LIU Xu-guang

2015, 30(2): 133-140.

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Graphene oxide (GO) prepared by the Hummers method was hydrothermally reduced for 5 and 10 h to obtain 5-RGO and 10-RGO, respectively. The GO and RGOs reacted with phenyl isocyanate to obtain three solution-processable functionalized graphenes (SPFGO, 5-SPFRGO and 10-SPFRGO), which were used as electron acceptors to prepare composite films with poly 3-hexylthiophene (P3HT) as an electron donor in polymer solar cells. Results indicate that GO consists of about 3-5 layers, and the RGOs still have some oxygen-containing functional groups such as —COOH and CO after the reduction. Functionalized GOs have good dispersibility in dichlorobenzene and exhibit energy levels matching P3HT, indicating that they can be used as the electron acceptor materials of polymer solar cells. A5-SPFRGO/P3HT composite film exhibits good compatibility, strong light absorption and obvious fluorescence quenching, suggesting that 5-SPFRGO is an excellent electron acceptor material.

Nanoporous carbons from oxidized green needle coke for use in high performance supercapacitors

WANG Jiu-zhou, WANG Li-qun, CHEN Ming-ming, WANG Cheng-yang, ZHANG Cui, HE Fei

2015, 30(2): 141-149. doi: 10.1016/S1872-5805(15)60180-9

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Green needle coke was oxidized by a mixture of HNO₃ and H₂SO₄ (3:7 vol/vol) acids. The resultant oxidized coke was separated into water dispersible and non-dispersible fractions, which were then activated by KOH using the same KOH/coke weight ratio to obtain two kinds of nanoporous carbons with different pore structures. The oxidized coke and the nanoporous carbons were characterized by XPS, XRD, TEM, N₂ adsorption and electrochemical tests. Results indicate that, at the same KOH/coke ratios, the nanoporous carbons derived from the water-dispersible oxidized coke have higher mass specific capacitances and capacitance retention ratios, and lower resistances than those from the non-dispersible ones when used as an electric double layer capacitor electrode in 6 mol/L KOH, but the former have a lower volumetric specific capacitance than the latter.

Spontaneous reduction of palladium chloride on surface of carbon materials to produce electrochemical catalysts for ethanol oxidation

SUN Li-zhi, YI Qing-feng

2015, 30(2): 150-155.

Abstract(723)

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Pd nanoparticles (Pd-NPs) were deposited on the surface of Vulcan XC-72 carbon black (CB), multi-walled carbon nanotubes (MWCNTs) and carbon spheres (CSs) by the spontaneous reduction of PdCl₂ with oxygen-functional groups on the carbon surfaces to produce catalysts for the electrochemical oxidation of ethanol. These carbons were also modified with a cationic surfactant (hexadecyltrimethyl ammonium bromide, CTAB) and subsequently used as supports for the deposition of Pd nanoparticles using the spontaneous reduction method. SEM, TEM and XRD were used to characterize their structures. Pd-NPs with a size of ca. 9 nm were obtained on the surface of the CTAB-modified MWCNTs. The amount of Pd-NPs spontaneously deposited on the CTAB-MWCNTs is much larger than that on the MWCNTs, CB or CSs. The Pd/CTAB-MWCNTs exhibit a higher anodic peak current density of 44.2 mA·cm^-2 in cyclic voltammetry, indicating a better electrocatalytic activity for ethanol oxidation than the other catalysts.

Effect of micropore and mesopore structure on CO₂ adsorption by activated carbons from biomass

SONG Tao, LIAO Jing-ming, XIAO Jun, SHEN Lai-hong

2015, 30(2): 156-166. doi: 10.1016/S1872-5805(15)60181-0

Abstract(879)

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Activated carbons (ACs) were produced by a one step process with CO₂ as the physical activation agent at 800 ℃. The ACs were further activated chemically using KOH, HNO₃ or CH₃COOH and heat-treated at 300 or 600 ℃ for 1 or 2 h to modify their properties. The effect of CO₂ concentration, activation time, types of chemical agents and the post heat-treatment conditions on CO₂ capture were investigated. Results showed that the optimum conditions for AC production from corn stalks was at 800 ℃ for 30 min with a CO₂ concentration of 20% during the physical activation. Chemical agents and further heat-treatment modified the pore structure of the ACs, resulting in a performance improvement for CO₂ adsorption. The BET surface area of one sample (HNO₃ activation +100 ℃ water bath 1 h + post heat-treatment at 600 ℃ for 2 h) was 639. 8 m²/g. The maximum CO₂ adsorption capacity of the sample was 7.33%, which is higher than that of a commercial AC (6.55%). The CO₂ adsorption is dominantly dependent on the mesopore volume when the BET surface area is smaller than 500 m²/g while the adsorption is closely associated with micropore area when the BET surface area is larger than 500 m²/g. The adsorption kinetics agreed well with the Bangham kinetic model.

Preparation of rubber wood sawdust-based activated carbon and its use as a filler of polyurethane matrix composites for microwave absorption

Azizah Shaaban, Sian-Meng Se, Imran Mohd Ibrahim, Qumrul Ahsan

2015, 30(2): 167-175. doi: 10.1016/S1872-5805(15)60182-2

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Activated carbons were prepared from rubber wood sawdust by chemical activation using ZnCl₂ as an activation agent at 500 ℃ for 60 minutes with ZnCl₂/dried rubber wood sawdust mass ratios from 1.0 to 2.0. Flat polyurethane (PU) composites filled with the activated carbons were prepared by a chemical foaming method using different loading amounts of the activated carbons to investigate their complex permittivity and the microwave absorption properties for use in electromagnetic interference (EMI) shielding. It was found that the best activated carbon is obtained at a ratio of 1.5, which has the highest Brunauer-Emmett-Teller surface area and a micropore volume of 1 301 m²/g and 0.37 cm³/g, respectively. With increasing activated carbon content, the dielectric constant (ε') and the return loss increase in the frequency range of 1-3 GHz. The composite filled with 8% activated carbon has a maximum dielectric constant of 3.0 and its return loss is above 10 dB at the global system mobile phone frequency of 1.8 GHz. Its EMI shielding efficiency is in the useful range of approximately 3 dB over a wide frequency range of 1-2.5 GHz. Compared with conventional materials such as polyethelene and polyester filled with metal additives, this composite is suitable for microwave absorption and is a potential candidate for EMI shielding applications.

Rheological properties of mesophase pitch investigated by the Giseeler fluidity method

JIN Ming-lin, CHENG Jie-ling, WANG Lian-xing, JIN Shuang-ling, ZHANG Rui

2015, 30(2): 176-180. doi: 10.1016/S1872-5805(15)60183-4

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The Giseeler fluidity method was used to investigate the rheological properties of pitch with and without heat treatment from room temperature to 520 ℃. Results show that the fluidity has a good repeatability at different temperatures under different heating rates. The fluidity of the raw pitch slowly increases from 253 to 282 ℃, then increases exponentially from 282 to 311 ℃ near the softening temperature, and finally remains unchanged from 311 to 498 ℃. This changing pattern of fluidity with temperature has also been found for heat-treated mesophase pitch and can be formulated by the Arrhenius equation, from which the viscous flow activation energy can be obtained. The toluene-insoluble fraction increases from 67.3% to 88.7% with heat-treatment time and the flow activation energy of the treated mesophase pitch in the Newtonian fluid region at low temperature range is between 203.6 and 294 kJ/mol.

Preparation of a nanodiamond colloid from nanodiamond powder resulting from explosive detonation

YANG Yu-dong, XU Jing-hua, YANG Lin-mei

2015, 30(2): 181-185.

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Nanodiamond powder obtained by explosive detonation with an average particle size of 360nm was oxidized by an acid mixture containing concentrated H₂SO₄ (98%) and H₃NO₃ (70%) with a volume ratio of 3:1, then dispersed with sonication in a polyethylene glycol solution(PEG200), and finally irradiated with a 1 064 nm laser for 1 h to prepare a stable nanodiamond colloidal solution. TEM, XRD, FTIR, VSM and PL spectroscopy were used to characterize the properties of the nanodiamond particles, such as morphology, particle size, microstructure, luminescence and magnetic properties. Results show that the acid oxidation introduces surface functional groups on the nanodiamond powder, but there are still amorphous carbon and secondary aggregates in the stable nanodiamond suspension in PEG200 before the laser irradiation. Amorphous carbon is removed and the aggregates in the nanodiamond suspension are broken into primary nanoparticles of 5 nm with the laser irradiation. The well-dispersed nanodiamond colloid in PEG200 solution after laser irradiation shows strong ferromagnetism and a high concentration of CC and C—OH bonds that favors the formation of the stable colloidal solution.

Synergistic flame retardant effects of composites containing organic montmorillonite, Nylon 6 and 2-cyclic pentaerythritoloctahydrogen tetraphosphate-4,6-benzene sulfonic acid sodium ammion-triazine

WANG Chao, LI Ying-chun, HU Guo-sheng, CAO Dong-hao

2015, 30(2): 186-192. doi: 10.1016/S1872-5805(15)60184-6

Abstract(786)

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A novel P-N containing intumescent flame retardant, 2-cyclic pentaerythritoloctahydrogen tetraphosphate-4,6-benzene sulfonic acid sodium ammion-triazine (CTOB) was synthesized and used as an additive in intumescent flame retardant composites containing organic montmorillonite (OMMT) and Nylon 6. The thermal stability and flammability properties of Nylon 6, CTOB, OMMT and their composites were investigated by TGA, limiting oxygen index (LOI) and cone calorimeter tests. Synergistic effects between CTOB and OMMT in the Nylon 6/CTOB/OMM composite were observed. A combination of CTOB and OMMT improved the thermal stability and the flammability properties of Nylon 6 and increased the LOI value to 28.0%. The average and peak heat release rates of the ternary composite were reduced by about 65.7 and 49.3%, respectively, compared with those of Nylon 6. The residue generated after the cone calorimeter tests upon combustion of the ternary composite was a compact and dense char as revealed by SEM, which is critically important for an excellent flame retardant.

2015 Vol. 30, No. 2

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