carbon fibre-reinforced silicon carbide composites (c/Sic) are a type of high-temperature structural ceramics that can be widely applied in aerospace, hypersonic aircraft, and military fields. However, the practical a...
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carbon fibre-reinforced silicon carbide composites (c/Sic) are a type of high-temperature structural ceramics that can be widely applied in aerospace, hypersonic aircraft, and military fields. However, the practical application of such materials in some complex high-temperature environments is still limited owing to drawbacks such as the bulging problem. In this study, the bulging of a c/Siccoating in a high-temperature wind tunnel is investigated. The surface data of specimens in the high-temperature arc wind tunnel were obtained using optical visualisation equipment, and the entire process of the formation of coating bulges, and their evolution and fusion is illustrated. Then, a fully coupled thermal fluid-solid simulation model is established, and the influence of defects on the internal heat transfer of materials is analysed. Further, the thermal fluid-solid coupling simulation technology is also used to analyse the bulging process of the coating to understand the mechanism of chemical reactions in defects between the coating and substrate. This work can serve as a guide for the screening and improvement of the material coating process.
作者：
Huang, WenkaiXu, FuhuaLiu, XiangChina Three Gorges Univ
Engn Res Ctr Ecoenvironm Three Gorges Reservoir R Key Lab Inorgan Nonmetall Crystalline & Energy Co Coll Mat & Chem EngnMinist Educ Yichang 443002 Hubei Peoples R China
Sodium borohydride has been widely regarded as a promising hydrogen carrier owing to its greatly hydrogen storing capability (10.8 wt%), high weight density and excellent stability in alkaline solutions. Herein, we fi...
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Sodium borohydride has been widely regarded as a promising hydrogen carrier owing to its greatly hydrogen storing capability (10.8 wt%), high weight density and excellent stability in alkaline solutions. Herein, we first design and synthesize a series of bimetallic M-Ru/c nanocomposites (including Fe-Ru/c, co-Ru/c, Ni-Ru/c and cu-Ru/c), via simply alloying of commercial Ru/c with nonprecious metal, for superior H2 evolution from the NaBH4 hydrolysis. The result exhibits that H2 generation is synergetically improved by alloying Ru/ c with co or Ni, while it is hindered by alloying Ru/c with Fe or cu. Indeed, co-Ru/c presents the highest efficient catalytic activity for H2 generation, with the TOF of 117.69 mol(H2)center dot molRu-1 center dot min-1, whereas Ru/c is only 57.08 mol(H2)center dot molRu-1 center dot min-1. In addition, the TOF of co-Ru/c reaches to 436.51 mol(H2)center dot molRu-1 center dot min-1 (96.7 L(H2)center dot gRu-1 center dot min-1) in the presence of NaOH. (c) 2021 Hydrogen Energy Publications LLc. Published by Elsevier Ltd. All rights reserved.
An environment-friendly oxidation-reduction method was used to prepare Pd/c hybrid nanocomposites (Ncs) using carbon as host and Pd nanoparticles (NPs) as surface loading, and sodium citrate was used as a reducing age...
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An environment-friendly oxidation-reduction method was used to prepare Pd/c hybrid nanocomposites (Ncs) using carbon as host and Pd nanoparticles (NPs) as surface loading, and sodium citrate was used as a reducing agent. The structures and morphologies of the Pd/c hybrid Ncs were characterized by X-ray diffraction, transmission (high-resolution) electron microscopy (TEM, HRTEM), X-ray photoelectron spectroscopy and so on. The results demonstrated that the Pd NPs were deposited on the surface of the c sphere beads, and the Pd NPs were homogeneous and monodispersed. The results also indicated that the diameter of the Pd NPs was 3 +/- 0.5 nm and the Pd/c Ncs were 197 +/- 6.5 nm. In addition, the Pd/c Ncs showed improved electrocatalytic activity for formic acid oxidation in comparison with commercial Pd NPs through controlling the surface structures. So, the environment-friendly preparation method provided developmental direction to fabricate all kinds of metal/c hybrid Ncs architectures.
Sicceramiccoating, for prevention of c/ccomposites against oxidation, was prepared by pressure-less reactive sintering to investigate the oxidation behaviour in an oxidising environment containing water vapour at 1...
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Sicceramiccoating, for prevention of c/ccomposites against oxidation, was prepared by pressure-less reactive sintering to investigate the oxidation behaviour in an oxidising environment containing water vapour at 1773 K. The experimental results demonstrated that the oxidation behaviour of porous Sicceramics could be divided into two stages, following the parabolic model, which was attributed to the variation in the contact area involved in the oxidation reactions. During the entire oxidation process, water vapour could accelerate the oxidation of the Sicceramics, according to the weight change. By first-principle calculations, the accelerated oxidation rate of the Sicceramics was attributed to weakened Si?O and Al?O bonds in the formed glassy scale, which were caused by hydroxide radicals from the water. Atomic thermal motions at high temperature could lead to the breakage of the network structure, promoting the diffusion and solution of oxidising gases. When the as-prepared Sicceramics were applied as anti-oxidative coatings for the c/ccomposites, the Sicceramiccoating and c/c matrix could be sealed and protected faster per unit time, because water vapour was beneficial to the formation of a glassy layer. The weight loss of the c/c matrix could be attributed to unsealed microcracks inside the Siccoating in the initial stage.
Silicon (Si) material, with high specificcapacity (4200 mAh/g) and low discharge voltage, is considered as one of the most ideal, promising, and alternative anode materials in next-generation lithium-ion battery (LIB...
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Silicon (Si) material, with high specificcapacity (4200 mAh/g) and low discharge voltage, is considered as one of the most ideal, promising, and alternative anode materials in next-generation lithium-ion battery (LIBs). In order to resolve the internal drawbacks of Si and reduce the process cost, the Si recycled from the kerf waste of photovoltaic industry was used as raw material. A silane-coupling agent 3-2 (2-sminoethylamino) propyltrimethoxysilane (DAMO) and a binder (PAA) was used to prepare Si@DAMO composite material with cross-linked net structure. Then, the polyvinyl pyrrolidone (PVP) containing N element was coated on the Si@DAMO. After carbonization, the c/Si@DAMO composite material with cross-linked net structure was obtained. The as-prepared c/Si@DAMO anode delivered an initial capacity of around 2841.6 mAh/g, and it remained a reversible capacity of 2066.7 mAh/g after 200 cycles at the current density of 0.1 c. At the rate testing from 0.1 to 1 c, the discharge capacities were 2593.39 mAh/g, 2362.95 mAh/g, 2082.08 mAh/g, 1882.44 mAh/g, 1704.57 mAh/g, and 1545.32 mAh/g, respectively. It retained 2084.88 mAh/g when back to 0.1 ccharge rate after 60 cycles. Therefore, it suggests that the as-prepared c/Si@DAMO is a potential anode material for LIBs.
In this work, we adopted PIP technology to introduce Sicceramics into the carbon fiber bundles of c/c-Siccomposites. The obtained c/c-Siccomposites containing PIP-Sic exhibited improved flexural strength. Meanwhile...
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In this work, we adopted PIP technology to introduce Sicceramics into the carbon fiber bundles of c/c-Siccomposites. The obtained c/c-Siccomposites containing PIP-Sic exhibited improved flexural strength. Meanwhile, the strength difference was reduced in in-plane and vertical directions. Fracture morphology revealed that the introduction of Sic into the fiber bundles broadened available toughening mechanism of the prepared composites. The braking performance of the materials was tested on an MM-1000 dynamometer. After braking at different speeds, we analyzed wear rates, variations in friction coefficient, and the morphological evolution of the friction surface. The results indicated that the introduction of Sic into the fiber bundles enhanced the abrasive resistance of local c/c regions, which yielded a significant reduction of the wear rates.
The impact of the organiccarbon to nitrate ratio (c/N ratio) on mixotrophic denitrification rate has been scarcely studied. Thus, this work aims to investigate the effect of the c/N ratio on the mixotrophic denitrifi...
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The impact of the organiccarbon to nitrate ratio (c/N ratio) on mixotrophic denitrification rate has been scarcely studied. Thus, this work aims to investigate the effect of the c/N ratio on the mixotrophic denitrification when methanol is used as a source of organic matter and elemental sulfur as an electron donor for autotrophic denitrification. For this, two initial concentrations of NO3--N (50 and 25 mg/L) at a stoichiometric ratio of S-0/N, and four initial c/N ratios (0, 0.6, 1.2, and 1.9 mg cH3OH/mg NO3- -N) were used at 25 (+/- 2) degrees c. The results showed that when using a c/N ratio of 0.6, the highest total nitrogen removal was obtained and the accumulation of nitrites was reduced, compared to an autotrophic system. The most significant contribution to nitrate consumption was through autotrophic denitrification (AuDeN) for a c/N ratio of 0.6 and 1.2, while for c/N = 1.9 the most significant contribution of nitrate consumption was through heterotrophic denitrification (HD). Finally, organic supplementation (methanol) served to increase the specific nitrate removal rate at high and low initial concentrations of substrate. Therefore, the best c/N ratio was 0.6 since it allowed for increasing the removal efficiency and the denitrification rate.
This study analyzed the influence of the sample volume, number of tested specimen, and testing method on the flexural strength of fabric-reinforced ceramic matrix composites. For this purpose, seven different batches ...
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This study analyzed the influence of the sample volume, number of tested specimen, and testing method on the flexural strength of fabric-reinforced ceramic matrix composites. For this purpose, seven different batches of c/cSic were prepared with four different sample thicknesses to determine the flexural strengths and Weibull moduli by three-and four-point flexural tests. The result showed that c/c-Sic exhibits a size effect of strength under bending load because a decrease of measured flexural strength with increased specimen size was observed. This size effect was discussed regarding the Weibull weakest link approach and the concept of quasi-brittle materials. The determined Weibull moduli were comparable for the same load condition but dissimilar for the identical material if the load condition were changed from three-to four-point bending. Hence, the Weibull modulus was found to be not an inherent material constant for c/c-Sic and the Weibull weakest link approach seems not appropriate.
carbon/silicon carbide (c/Sic) composites are usually regarded as thermal protective system materials and widely applied in hypersonic vehicles or ramjet. However, poor thermal conductivity of c/Siccomposites, leadin...
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carbon/silicon carbide (c/Sic) composites are usually regarded as thermal protective system materials and widely applied in hypersonic vehicles or ramjet. However, poor thermal conductivity of c/Siccomposites, leading to severe heat concentration and thermal stress during the high-speed operation of hypersonic vehicle, limits their broad-range of practical applications. Modification with high thermal conductive fillers is an optional method;however, controllable dispersion and orientation of the fillers to construct continuous and ordered heat conductive channel has been proven to be a challenging task. Herein, based on high thermal conductivity fibers, a three-dimensional micro-pipeline preform was developed for the preparation of structure-function integrated c/Siccomposites. The technical feasibility of the method, the characteristics of microstructures, and the thermal conductivity and bending strength of the as-obtained composites were systematically studied. Results revealed that the thermal conductivities of as-obtained composites reached 150.2 and 46.7 W m-1 K-1 for in-plane and out-of-plane direction, respectively. The bending strength obtained herein is 264.4 MPa, which is lower than that of polyacrylonitrile c/Siccomposites. However, the fine control over the component and microstructure or densification could provide a higher value in the future research. In sum, the proposed method provides a convenient and feasible approach to prepare high thermal conductive c/Siccomposites.
Bamboos are productive grasses that currently yield a high-quality wood and potentially an abundance of lignocellulose for bioenergy. All are c-3 grasses of warm habitats, where they are prone to significant photoresp...
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Bamboos are productive grasses that currently yield a high-quality wood and potentially an abundance of lignocellulose for bioenergy. All are c-3 grasses of warm habitats, where they are prone to significant photorespiratory inhibition and competitive suppression by c-4 grasses. Here, we investigate whether three bamboo species from the Brazilian cerrado (Dendrocalamus asper, Guadua angustifolia, and Guadua magna) exhibit unique adaptations that suppress photorespiratory costs and enhance photosynthetic efficiency. We evaluated photosynthetic efficiency of the bamboos and rice (Oryza sativa) by measuring c-*, the cO2 compensation point in the absence of mitochondrial respiration. At 25celcius, c-* averaged 2.81 Pa in each of the bamboo species, which is closer to a c-2 plant (2.71 Pa) than the c-3 plant rice (3.31 Pa). Assuming a chloroplast cO2 concentration of 200 mu mol mol(-1), this represents an 18% lower cost of apparent photorespiration in bamboo than rice. Light and transmission electronic microscopy of the bamboo leaves exhibited few organelles in the bundle and mestome sheath cells, and mesophyll (M) cells are deeply lobed with 99% of the cell periphery adjacent to intercellular air space covered by chloroplast and stromules. The chloroplast layer in bamboo M cells is thick, with mitochondria adjacent to or engulfed by chloroplasts. This arrangement slows cO2 efflux and facilitates refixation of photorespired cO2, which could explain the low c-* in the bamboos. The bamboos also had higher water use efficiency than rice, which may reflect efficient refixation of photorespired cO2.
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