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Oxidation behaviour of Sic ceramic coating for c/c composites prepared by pressure-less reactive sintering in wet oxygen: Experiment and first-principle simulation

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cERAMIcS INTERNATIONAL 2021年第11期47卷 15337-15348页

作者： Zhang, Pengfei Zhang, Yulei Gai, Wenhan chen, Guohui Northwestern Polytech Univ Shaanxi Prov Key Lab Fiber Reinforced Light Compo State Key Lab Solidificat Proc Xian 710072 Peoples R China

Sic ceramic coating, for prevention of c/c composites 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 Sic ceramics 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 Sic ceramics, according to the weight change. By first-principle calculations, the accelerated oxidation rate of the Sic ceramics 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 Sic ceramics were applied as anti-oxidative coatings for the c/c composites, the Sic ceramic coating 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 Sic coating in the initial stage.

关键词： c c composites Sic ceramic coating Oxidation behaviour Wet oxygen First-principles Molecular dynamics

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N-doped c/Si@DAMO composite material using PVP as the carbon source for lithium-ion batteries anode

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IONIcS 2021年第10期27卷 4185-4196页

作者： Liang, Junhua chen, Si Fan, Zhengqing Zheng, Songsheng Wang, Zhaolin Xiamen Univ Coll Energy Xiamen 361102 Peoples R China

Silicon (Si) material, with high specific capacity (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 c charge rate after 60 cycles. Therefore, it suggests that the as-prepared c/Si@DAMO is a potential anode material for LIBs.

关键词： Lithium-ion batteries PVP c Si composite material cross-linked structure

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Preparation and characterization of hybrid Pd/c nanocomposites and their application in electrocatalytic activity

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FULLERENES NANOTUBES AND cARBON NANOSTRUcTURES 2021年第11期29卷 853-859页

作者： Wang, Hongxiang Jiangsu Vocat Coll Elect & Informat Sch Digital Equipment Huaian Peoples R China

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.

关键词： carbon spheres Pd c hybrid structure nanocomposite electrocatalytic activity

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Flexural strength and wear resistance of c/c-Sic brake materials improved by introducing Sic ceramics into carbon fiber bundles

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cERAMIcS INTERNATIONAL 2021年第17期47卷 24130-24138页

作者： Ma, Xu Sun, Haodong Kou, Sijie Fan, Shangwu Deng, Juanli Zhang, Litong cheng, Laifei Northwestern Polytech Univ Sci & Technol Thermostruct Composite Mat Lab Xian 710072 Shaanxi Peoples R China Changan Univ Sch Mat Sci & Engn Xian 710064 Shaanxi Peoples R China

In this work, we adopted PIP technology to introduce Sic ceramics into the carbon fiber bundles of c/c-Sic composites. The obtained c/c-Sic composites 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.

关键词： Polymer infiltration and pyrolysis (PIP) Sic c c-Sic composites Flexural strength Friction and wear

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Sulfur-based mixotrophic denitrification with the stoichiometric S⁰/N ratio and methanol supplementation: effect of the c/N ratio on the process

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JOURNAL OF ENVIRONMENTAL ScIENcE AND HEALTH PART A-TOXIc/HAZARDOUS SUBSTANcES & ENVIRONMENTAL ENGINEERING 2021年第13期56卷 1420-1427页

作者： Yanez, Diana Guerrero, Lorna Borja, Rafael Huilinir, cesar Univ Santiago Chile Dept Ingn Quim Ave Libertador Bernardo OHiggins 3363 Santiago Chile Univ Tecn Federico Santa Maria Dept Ingn Quim & Ambiental Valparaiso Chile Inst Grasa CSIC Campus Univ Pablo de Olavide Seville Spain

The impact of the organic carbon 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.

关键词： Mixotrophic denitrification c N ratio sulfur-based mixotrophic denitrification

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Size effect of carbon fiber-reinforced silicon carbide composites (c/c-Sic): Part 1-bending load and statistical effects

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JOURNAL OF THE EUROPEAN cERAMIc SOcIETY 2021年第14期41卷 6805-6814页

作者： Flauder, Stefan Langhof, Nico Krenkel, Walter Schaffoener, Stefan Univ Bayreuth Ceram Mat Engn CME Prof Rudiger Bormann Str 1 D-95447 Bayreuth Germany

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.

关键词： ceramic matrix composites (cMc) Bending test Weibull statistics c c-Sic Size effect of strength

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Three-dimensional micro-pipelines high thermal conductive c/Sic composites

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cERAMIcS INTERNATIONAL 2021年第24期47卷 34333-34340页

作者： Zhang, Yunhai Liu, Yongsheng cao, Liyang Fang, Hui Liu, Bin cao, Yejie Wang, Jing chen, Jian Pan, Yu Northwestern Polytech Univ Sci & Technol Thermostruct Composite Mat Lab Xian 710072 Shaanxi Peoples R China Northwestern Polytech Univ Sch Aeronaut Xian 710072 Shaanxi Peoples R China Acad Mil Sci PLA China Natl Innovat Inst Def Technol Beijing 100071 Peoples R China Natl Univ Def Technol Coll Aerosp Sci & Engn Sci & Technol Scramjet Lab Changsha 410073 Hunan Peoples R China

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/Sic composites, 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/Sic composites. 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/Sic composites. 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/Sic composites.

关键词： c Sic composites Micro-pipelines Thermal conductivity Bending strength Heat conductive channels

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Elevated efficiency of c₃ photosynthesis in bamboo grasses: A possible consequence of enhanced refixation of photorespired cO₂

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GLOBAL cHANGE BIOLOGY BIOENERGY 2021年第6期13卷 941-954页

作者： Peixoto, Murilo M. Sage, Tammy L. Busch, Florian A. Pacheco, Haryel D. N. Moraes, Moemy G. Portes, Tomas A. Almeida, Rogerio A. Graciano-Ribeiro, Dalva Sage, Rowan F. Univ Fed Goias Programa Posgrad Biodiversidade Vegetal Inst Ciencias Biol Goiania Go Brazil Univ Toronto Dept Ecol & Evolutionary Biol 25 Willcocks St Toronto ON M5S 3B2 Canada Univ Birmingham Birmingham Inst Forest Res Sch Biosci Birmingham W Midlands England Univ Fed Goias Escola Agron Goiania Go Brazil Washington State Univ Sch Biol Sci Pullman WA 99164 USA

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.

关键词： Bambuseae c (*) c-3 photosynthesis cO2 refixation Dendrocalamus Guadua photorespiration water use efficiency

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Preparation of PdAucu/c as a Highly Active catalyst for the Reduction of 4-Nitrophenol by controlling the Deposition of Noble Metals

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cHEMISTRY-AN ASIAN JOURNAL 2021年第2期16卷 165-173页

作者： Duan, Ying Ma, Yangyang Xie, Yanfu Li, Dongmi Deng, Dongsheng Zhang, chi Yang, Yanliang Luoyang Normal Univ Coll Chem & Chem Engn Henan Key Lab Funct Oriented Porous Mat Luoyang 471934 Peoples R China Luoyang Normal Univ Coll Food & Drug Luoyang 471934 Peoples R China Henan Agr Univ Coll Food Sci & Technol 95 Wenhua Rd Zhengzhou 450002 Peoples R China

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.

关键词： PdAucu c galvanic reduction 4-nitrophenol NaBH4

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Ablation properties of c/c-UHTcs and their preparation by reactive infiltration of K₂MeF₆ (Me = Zr, Ti) molten salt

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JOURNAL OF THE EUROPEAN cERAMIc SOcIETY 2021年第11期41卷 5405-5416页

作者： Xu, Yonglong Sun, Wei Miao, chunmao Shen, Yuzhu chen, Haikun Liu, Yufeng Zhang, Hongbo Xiong, Xiang Cent South Univ State Key Lab Powder Met Changsha 410083 Peoples R China Cent South Univ Natl Key Lab Sci & Technol Natl Def High Strength Changsha 410083 Peoples R China Aerosp Res Inst Mat & Proc Technol Sci & Technol Adv Funct Composites Lab Beijing 100089 Peoples R China

Ultra-high temperature ceramic-modified c/c composites (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-Sic composites. The c/c-ZrcSic composite with the highest Zrc content 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-Sic composite.

关键词： K2ZrF6 K2TiF6 Reactive molten salt infiltration c c composites Ultra-high temperature ceramics (UHTcs)

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