2018 Vol. 33, No. 2

Graphical Contents
2018, 33(2): .
Abstract(129) PDF(327)
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Carbon materials in a high temperature gas-cooled reactor pebble-bed module
ZHOU Xiang-wen, YANG Yang, SONG Jing, LU Zhen-ming, ZHANG Jie, LIU Bing, TANG Ya-ping
2018, 33(2): 97-108. doi: 10.1016/S1872-5805(18)60328-2
Abstract(416) PDF(312)
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Compared with the long use of carbon materials in human history, the debut of carbon materials in the Chicago Pile-1 nuclear reactor took place only 70 years ago. Since then, carbon materials have played important roles in nuclear reactors, especially in high temperature gas-cooled reactors (HTRs) because of their many excellent properties. As the most promising candidate for Generation IV reactors, a demonstration plant for HTRs, an HTR pebble-bed module (HTR-PM) is currently under construction in China. In the HTR-PM, carbon materials act as the core structural material, reflector, fuel matrix, moderator, and thermal and neutron shields. Because the dimensions and properties of the carbon are generally influenced by the high temperature and neutron irradiation in the HTR-PM, there are rigorous requirements for their performance. Since the precursor materials such as cokes and natural graphite, and the subsequent forming method play a critical role in determining the structure, properties and performance of the material under irradiation, a judicious selection of the raw materials and forming method is required to obtain the desired structure and properties. This paper introduces the detailed property requirements of different carbon materials in the HTR-PM and their fabrication processes. In addition, the current status and future commercialization of the HTR-PM in China and abroad are presented. In order to meet the requirement of full local production in a commercial HTR, long-term considerations such as the sustainable and stable supply of the raw materials, optimization of the manufacturing process in the local production of nuclear graphite for structural graphite and graphite pebbles, and the stable production and reduced cost of the precursor materials are discussed. Finally, current progress and future arrangements for the irradiation testing of Chinese nuclear graphite at the Oak Ridge National Laboratory (USA) are presented. This manuscript is intended to act as a reference for carbon material producers who intend to develop nuclear graphite and carbon materials for use in future commercial HTRs. Meanwhile, a great deal of information introduced in the manuscript is also useful for scientific researchers of carbon materials.
Fabrication of a Ru-NiAl layered double hydroxide-oxidized CNT hybrid catalyst for the selective oxidation of benzyl alcohol to benzaldehyde
SHAN Yuan-yuan, YU Chang, ZHANG Xu, ZHANG Meng-di, DONG Qiang, QIU Jie-shan
2018, 33(2): 109-115.
Abstract(428) PDF(415)
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A NiAl layered double hydroxide-oxidized CNT (NiAl-LDH-o-CNT) hybrid was synthesized by a mild hydrothermal method using o-CNTs, Al(NO3)3·9H2O and Ni(NO3)2·6H2O as the precursors. It was impregnated with RuCl3 as a catalyst for the oxidation of benzyl alcohol to benzaldehyde and its activity compared with NiAl-LDHs and o-CNTs. The crystal structure and morphological characteristics of the NiAl-LDH-o-CNTs hybrid were characterized by XRD and TEM. The characteristics of emulsions of NiAl-LDHs, o-CNTs and the hybrid in a water-toluene system were investigated by optical microscopy. It was found that among these supports, the hybrid was best emulsified with the narrowest and smallest droplet size distribution (ca. 90 μm) and the largest fraction (95%) of droplet volume. The activity and selectivity for benzyl alcohol oxidation to benzaldehyde increased with interface area for all the emulsions. The Ru/NiAl-LDH-o-CNTs hybrid had the best catalytic performance with the highest values of conversion and selectivity of 96% and 99.9%, respectively.
Nd-doped TiO2-C hybrid aerogels and their photocatalytic properties
SHAO Xia, PAN Feng, ZHENG Li, ZHANG Rui, ZHANG Wen-ya
2018, 33(2): 116-124. doi: 10.1016/S1872-5805(18)60329-4
Abstract(368) PDF(307)
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Nd-doped TiO2-C hybrid aerogels with different Nd doping levels were prepared by a combined sol-gel and impregnation method. The microstructure, morphology and photocatalytic activities of the samples were investigated by XRD, SEM, FTIR, XPS, nitrogen adsorption and the photocatalytic degradation of methylene blue (MB) under UV irradiation. Results showed that the samples are composed of irregular-shaped nanoparticles and the Nd dopant inhibits their growth. The TiO2 in the samples is anatase, the carbon is amorphous and Nd3+ is in a Ti-O-Nd bond form. The samples had strong absorption in the ultraviolet region and exhibited good degradation activity for MB in aqueous solutions under UV light. The best activity was achieved when the ratio of Nd to Ti is 3-4 wt%, in which case MB was completely degraded under UV irradiation for 160 min.
Preparation and properties of electrospun GO/PEO nanofibers
LENG Xiang-xing, CHIANG Sum-wai, DU Hong-da, KANG Fei-yu
2018, 33(2): 125-130.
Abstract(631) PDF(569)
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Bulk polymers have a very low thermal conductivity of about 0.2 W/m·K. Polymer nanofibers prepared by electrospinning have a much higher thermal conductivity along the fiber axis. Graphene oxide (GO) was dispersed in a polyethylene oxide (PEO) solution and the resulting dispersion was electrospun into GO/PEO nanofibers. The fiber with 0.5 wt% GO had a thermal conductivity of 22.9 W/m·K, which is two-orders of magnitude higher than bulk PEO. Polarized FT-IR shows that the PEO fibers had different spectra in directions parallel and perpendicular to polarized IR. The intensity ratio of the peak at 1 099 cm-1 between the parallel and perpendicular directions to the polarized IR was calculated. The curves of thermal conductivity and the intensity ratio against GO content are very similar, which suggests that molecular alignment is a key factor determining the thermal conductivity of the nanofibers. GO at low contents inhibits the movement of PEO chains because hydrogen bonds are formed between GO and a PEO chain during electrospinning and this improves the orientation degree of the PEO chain in the resulting GO/PEO nanofibers. With increasing GO content, the viscosity of the solution increases, which is unfavorable for the alignment of the PEO chain during electrospinning.
Synthesis and properties of a silane and copolymer-modified graphene oxide for use as a water-reducing agent in cement pastes
WANG Qin, LI Shi-yu, PAN Shuo, GUO Zi-wei
2018, 33(2): 131-139. doi: 10.1016/S1872-5805(18)60330-0
Abstract(626) PDF(536)
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The addition of graphene oxide (GO) to cement paste significantly increases its toughness, however its fluidity is adversely affected. GO was first reacted with vinyltrimethoxysilane to produce a silane-modified graphene oxide (S-GO), which was then copolymerized with acrylic acid and a water reducing agent, isobutaenol polyoxyethylene ether (molecular mass 2400), to obtain a silane and copolymer-modified GO (P-S-GO) which acted as a water-reducing agent of the cement paste. A copolymer without GO was prepared under the same conditions for comparison. The structure, elemental composition and dispersibility of GO, S-GO and P-S-GO in a simulated cement environment (saturated lime water) were investigated by FTIR, XRD and a sedimentation test. The fluidity and rheology of the cement pastes with added GO, copolymer or P-S-GO were investigated. Results showed that vinyltrimethoxysilane reacted with the -OH group on the GO sheets to form an ether bond and the copolymer was grafted onto a vinyl group of S-GO by an addition reaction to produce the P-S-GO. The P-S-GO has a better dispersibility in saturated lime water with a negligible amount of aggregation compared to GO and a significant agglomeration occurs for GO. The addition of the P-S-GO to the cement pastes improves the fluidity and rheological properties compared with GO, offsetting the negative impact of GO and increasing the toughness of the resulting cements.
Piezoresistive response of carbon nanotube yarns under tension: Parametric effects and phenomenology
Jude C. Anike, Kalayu Belay, Jandro L. Abot
2018, 33(2): 140-154. doi: 10.1016/S1872-5805(18)60331-2
Abstract(329) PDF(272)
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Carbon nanotubes (CNTs) are inherently sensitive to mechanical strain, making them ideal for sensing in composites. Because of this they were purposefully spun into macroscopic yarns to permit their utilization in structural components. This experimental study aims to determine the effect of quasi-static strain rate, mechanical properties and geometry of the CNT yarns on their piezoresistivity. Strain rates affect the failure mechanisms and electromechanical properties of CNT yarns, with high strain rates showing increased tensile strength and a positive piezoresistivity with low strain rates favoring a higher strain-to-failure and a negative piezoresistivity. The sensitivity or gauge factor (GF) of the free CNT yarn remains relatively unchanged with varying strain rates (GFs between 0.12-0.20 at 2.5% strain) but is strongly dependent on the strain level (GFs:0.2, 0.5, 0.4 and 0.2 at 0.5, 1, 1.5 and 2.5% strains, respectively) and diameter (GFs:0.16 and 0.29 at 3% strain for~25 μm and 50 μm diameter yarns, respectively). The linearity needed for a robust sensor is favored at higher strain rates with correlation coefficients more than 0.995 compared to values less than 0.832 at lower strain rates.
Preparation of C/C-Cu composites from C/C by first modifying the precursor with Mo2C
ZHOU Wen-yan, PENG Ke, RAN Li-ping, GE Yi-cheng, YI Mao-zhong
2018, 33(2): 155-161.
Abstract(488) PDF(310)
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Two C/C preforms were prepared by the chemical vapor infiltration of pyrocarbon into needle-punctured carbon fiber felts to a density of 1.5 g/cm3, followed by or without graphitization at 2300℃. The two preforms were first treated in a KCl-LiCl molten salt mixture (mol/mol=59:41) containing 10 wt% ammonium molybdate at 1000℃ for 1 h to form a Mo2C layer on pore walls of the preforms, then leached with deionized water to remove the KCl and LiCl, and finally vacuum-infiltrated with liquid copper at 1200℃ for 1 h to obtain C/C-Cu composites. Results indicate that the thicknesses of the Mo2C layers are 2.5 and 3 μm for the preforms with and without graphitization, respectively. The Mo2C layer improves the wetting of the pore walls by copper, which makes the copper infiltration complete. Local Raman spectroscopy shows that the intensity ratio of the G and D bands of the pyrocarbon is higher near carbon fibers while this trend is reversed after the molten salt treatment, indicating that the Mo2C layer causes catalytic and stress-induced graphitization effects for the pyrocarbon in both preforms.
Synthesis of a biocompatible nanoporous carbon and its conjugation with florescent dye for cellular imaging and targeted drug delivery to cancer cells
S. Yallappa, Shoriya Aruni Abdul Manaf, Gurumurthy Hegde
2018, 33(2): 162-172. doi: 10.1016/S1872-5805(18)60332-4
Abstract(332) PDF(249)
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A nanoporous carbon (NPC) was synthesized from Oil palm leaves (OPL) by pyrolysis at 600℃ in a N2 atmosphere, oxidized by a mixture of sulfuric and nitric acids (3:1 vol/vol) and conjugated with coumarin-6 as a fluorescence dye for cellular imaging and drug delivery to cancer cells. The structure, morphology and dispersion stability of NPC in aqueous media before and after the conjugation were investigated by XRD, FT-IR, Raman spectroscopy, SEM, TEM and zeta potential measurement. Cell uptake for the conjugated NPC was investigated by fluorescence microscopy. Results indicate that the cellulose, hemicelluloses and lignin in OPL convert to a graphitic structure by pyrolysis. NPC consists of spherical nanoparticles with diameters of 30-50 nm and has a high graphitic content with an ID/IG ratio of 0.7. The coumarin-6 is successfully conjugated to NPC by forming a complex. Both NPC and the conjugated NPC have a high dispersion stability in aqueous media. NPC is biocompatible with a negligible cytotoxicity. The conjugated NPC exhibits a high cell uptake, is highly biocompatible for normal cells and toxic for tested human cancer cells. NPC is a good candidate for cellular imaging and targeted drug delivery.
Effects of a natural flake graphite addition to mesophase pitch on the structure and properties of unidirectional C/C composites
LI You, YUAN Guan-ming, LI Xuan-ke, DONG Zhi-jun, CONG Ye, ZHANG Zhong-wei, WANG Jun-shan
2018, 33(2): 173-182.
Abstract(331) PDF(369)
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Unidirectional carbon/carbon composites were prepared by hot-pressing mesophase pitch-based carbon fibers as the conductive filler phase and mesophase pitch containing natural flake graphite as the binder/matrix at 500℃ followed by carbonization at 1000℃ for 1 h and graphitization at 2900℃ for 1 h. The morphology and microstructure of cross-sections of the samples were characterized by polarized-light microscopy and scanning electron microscopy. The effect of adding natural flake graphite to the mesophase pitch on the thermal conductivity of the composites was investigated. Results show that the graphite addition has little effect on the bulk densities of the composites, but has a significant impact on the thermal conductivities in different directions. With increasing the graphite content and particle size, the thermal diffusivity of the composites in the longitudinal direction of the fibers decreases while that in the perpendicular direction increases. With a graphite addition of 16 vol% and an average graphite particle size of 60 μm, the longitudinal thermal diffusivity of the composite decreases from 650.5 to 510.9 mm2/s while the perpendicular thermal diffusivity increases from 22.4 to 48.9 mm2/s. The flexural strength of the composites perpendicular to the fibers is also increased by 29% by adding graphite.
Preparation of a biochar with a high calorific value from chestnut shells
JIANG Ke-mao, CHENG Chao-ge, RAN Min, LU Yong-gen, WU Qi-lin
2018, 33(2): 183-187. doi: 10.1016/S1872-5805(18)60333-6
Abstract(388) PDF(298)
Abstract:
The recovery of biomass provides a solution for solving the energy shortage problem. Chestnut shells consist of cellulose, hemicellulose and lignin, and have a low calorific value. We propose a method to produce a biochar with a high calorific value from chestnut shells by catalytic pre-oxidation and pyrolysis with sulfuric acid and urea. The pyrolysis behavior and the changes in structure and properties were investigated. Results indicate that the catalysts slow the pyrolysis reaction, leading to a high-quality char. The carbon content and calorific value are related to the pyrolysis temperature. When the chestnut shells are pyrolyzed at 750℃, the yield and calorific value of the char are 44.31 wt% and 35.48 MJ/Kg, respectively. The calorific value of the char is higher than that of first-level cleaned coal (30.00 MJ/Kg).
Improved decontamination performance of biofilm systems using carbon fibers as carriers for microorganisms
AN Yong-zhen, WANG Chun-hua, MIAO Peng, WANG Xiao-xu, LIANG Jie-ying, LIU Jie
2018, 33(2): 188-192. doi: 10.1016/S1872-5805(18)60334-8
Abstract(377) PDF(367)
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Biofilm carriers and effective microorganisms (EMs) are both important to improve the decontamination performance of biofilms for wastewater. The decontamination performance of biofilms using polyester (PET), polyvinyl alcohol (PVA), carbon fibers (CFs) and electrochemically-treated CFs as biofilm carriers for EMs were investigated by comparing the concentrations of the chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) of wastewater at different stages of decontamination. The use of all carriers efficiently prevents the loss of mobile EMs. The use of CFs increases the decontamination efficiency. Electrochemically-treated CFs perform best, and the corresponding biofilm has a strong resistivity to the surrounding environment and achieves 97.1, 92.5 and 96.0% removal rates for COD, TN and TP, respectively, which are 5%-67% higher than those obtained using PET and PVA as carriers.