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.
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.
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.
The reasonable control of the dispersion of noble metals is an important topic for heterogeneous catalysts. In this manuscript, Pdcu/c, Aucu/c and PdAucu/c were prepared by the galvanic reduction method to ensure that...
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The reasonable control of the dispersion of noble metals is an important topic for heterogeneous catalysts. In this manuscript, Pdcu/c, Aucu/c and PdAucu/c were prepared by the galvanic reduction method to ensure that Pd and Au follow the distribution of cu nanoparticles. The catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), energy-dispersive spectrometer elemental mappings and lines scans. Both the Pd and Au had very high dispersion no matter whether they were introduced individually or simultaneously. The Pd and Au were distributed mainly on the cu nanoparticles as evidenced by the energy-dispersive spectrometer elemental mappings and lines scans. The reduction of 4-nitrophenol was used as a model reaction for the prepared catalysts. Pdcu/c and Aucu/c showed high activity for this reaction compared to the literature, and the activity could be further increased by the introduction of Pd and Au in an appropriate ratio at the same time. The normalized reaction rate reached 2.005 s(-1) mM(-1) for the PdAucu/c-2.0, in which the mole ratio of Pd to Au was 2.0.
Ultra-high temperature ceramic-modified c/ccomposites (c/c-UHTcs) were prepared by the reactive infiltration of K2MeF6 (Me = Zr, Ti) mixed with Si and Zr-Si powders. Molten salt infiltration can be divided into two s...
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Ultra-high temperature ceramic-modified c/ccomposites (c/c-UHTcs) were prepared by the reactive infiltration of K2MeF6 (Me = Zr, Ti) mixed with Si and Zr-Si powders. Molten salt infiltration can be divided into two stages: salt ion melt and Me-Si alloy melt. In the temperature range below 1400 degrees c, Zr and Si dissolve in the molten salt, are carried by the ion melt, and precipitate at the Pyc interface to form carbides. Above 1400 degrees c, a large amount of molten salt volatilises and thermally decomposes. The Me-Si alloy forms a melt and infiltrates the c/c matrix, and finally forms c/c-Zrc-Sic, c/c-Ti3Sic2-Sic, and c/c-Zrc-Tic-Siccomposites. The c/c-ZrcSiccomposite with the highest Zrccontent exhibited the lowest mass rate (2.6 +/- 0.02 mg/s) and linear ablation rate (0.82 +/- 0.04 mu m/s), which were reduced by 43.5 and 50.8 %, respectively, compared to the unmodified c/cZrc-Siccomposite.
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