CERAMICS INTERNATIONAL
·
2022
·
IF 5.532
Xiumei Wu,Shu Yu,Yunping Li
Silicon oxycarbide (SiOC) films on C/C composite substrate were prepared by isothermal chemical vapor deposition (CVD) with hexamethyldisilazane (HMDSN) as precursor. The deposition rate, microstructure, composition and mechanical properties of films prepared at deposition temperature ranging from 1300 K to 1576 K were investigated in details. With increasing deposition temperature, deposition rate increased gradually and reached a maximum value of 42.9 μm/h at 1513 K and then decreased; concurrently, the surface morphology of SiOC film changed from a smooth-dense to a coarse cauliflower, and then into a needle-like granular morphology. The SiOC films were composed of dominant SiC and a few other phases at all temperatures. In addition, the contents of oxygen-enriched units SiO 3 C and SiO 2 increased with deposition temperature due to redistribution reaction of Si –O and Si –C bonds and oxidation . SiOC films prepared at 1373 K showed the highest hardness and elastic modulus for 28.8 GPa and 234.2 GPa, respectively. SiOC films also contained small amounts of Si 3 N 4 and SiCN at all conditions.
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高影响因子
CEMENT AND CONCRETE RESEARCH
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2021
·
IF 10.933
Xueyu Pang,Lijun Sun,Fang Sun,Ge Zhang,Shenglai Guo,Yuhuan Bu
The heat evolution during the hydration of cement was examined by multiple calorimetric methods: isothermal , oscillating isothermal, as well as temperature scanning tests in the temperature range from 15 °C to 95 °C. The apparent activation energy ( E a ) of several different types of cements were all found to decrease significantly with temperature. Type of additives and water to cement ratio had little influence on the temperature dependence of E a . The correlation between E a and temperature may be mathematically simplified to a step function, where E a is a nonzero constant below a critical temperature ( T cr ) and reduces to zero above that temperature. The proposed model of E a was combined with a scale factor model to simulate the influence of curing temperature on the hydration kinetics of cement with significantly improved accuracy compared to an earlier model.
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高影响因子
CERAMICS INTERNATIONAL
·
2021
·
IF 4.527
Fuhai Liu,Maozhong Yi,Liping Ran,Yicheng Ge,Ke Peng
In this study, with 2.5D needle punched carbon felt as reinforcement, hexagonal boron nitride (h-BN) was introduced through chemical vapor infiltration (CVI) and slurry impregnation (SI) methods, and then pyrocarbon was deposited through CVI to convert the BN-containing preform into carbon fiber reinforced carbon-boron nitride binary matrix composites (C/C-BN). The microstructure and mechanical properties of C/C-BN(P) composites prepared by SI combined with CVI were compared with those of C/C-BN(CVI) composites prepared by CVI. The tribological behavior of C/C-BN(P) composites containing different contents of h-BN fillers and C/C-BN(CVI) composites with and without heat treatment was investigated by the ball-on-disk technique in dry sliding conditions using GCr15 steel balls and Si 3 N 4 balls as sliding counterparts at two different sliding speeds (v = 0.2 and 0.8 m/s), and compared with the C/C composites used as a reference. C/C-BN(P) composites exhibit improved tribological behavior, which can be explained by the combined effect of SI and CVI on the microstructure and mechanical properties, leading to changes in the wear mechanism of the C/C-BN composites. The excellent reinforcement is attributed to the integrity structure of the C/C-BN(P), which can make the self-lubricating friction layer stably exist on the surface of the material and significantly reduce the friction coefficient and wear loss of the C/C-BN(P) composite. Furthermore, the mechanical and tribological properties of C/C-BN(P) composites can be adjusted by using different volume content of h-BN. The present work shows that C/C-BN(P) composites have wide application prospects as anti-friction and wear-resistant materials.
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Nature Communications
·
2020
·Vol. 11
·期 1
·1-11
·
IF 12.121
Cao Wenbo,Cheng Simin,Yang Jing,Feng Jiaxin,Zhang Wenpeng,Li Zishuai,Chen Qinhua,Xia Yu,Ouyang Zheng,Ma Xiaoxiao
Lipids play a pivotal role in biological processes and lipid analysis by mass spectrometry (MS) has significantly advanced lipidomic studies. While the structure specificity of lipid analysis proves to be critical for studying the biological functions of lipids, current mainstream methods for large-scale lipid analysis can only identify the lipid classes and fatty acyl chains, leaving the C=C location and sn -position unidentified. In this study, combining photochemistry and tandem MS we develop a simple but effective workflow to enable large-scale and near-complete lipid structure characterization with a powerful capability of identifying C=C location(s) and sn -position(s) simultaneously. Quantitation of lipid structure isomers at multiple levels of specificity is achieved and different subtypes of human breast cancer cells are successfully discriminated. Remarkably, human lung cancer tissues can only be distinguished from adjacent normal tissues using quantitative results of both lipid C=C location and sn -position isomers.
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PubMed
高影响因子
ACS Catalysis
·
2019
·
IF 12.221
Huifang Liu,Hongji Li,Nengchao Luo,Feng Wang
Lignin is the largest carrier of aromatics on earth, and its depolymerization can afford value-added aromatic products. Direct cleavage of the C–C bonds in lignin linkages is significant, but it is challenging to obtain low-molecular-weight aromatic monomers. Herein, using vanadium catalysts under visible light, we selectively cleave the C–C bonds in β-1 and β-O-4 interlinkages occluded in lignin models and extracts by an oxidative protocol. Visible light irradiation triggered single electron transfer between the substrate and the catalyst, which further induced the selective Cα–Cβ bond cleavage and generated the final aromatic products through radical intermediates. Using this photocatalytic chemistry, the reactivity of lignin models and the selectivity of Cα–Cβ bond cleavage were significantly improved. More importantly, this protocol affords aromatic monomers through the fragmentation of organosolv lignins even at room temperature, indicating the potential of photocatalytic C–C bond cleavage of lignin linkages under ambient conditions.
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高影响因子
JOURNAL OF THE EUROPEAN CERAMIC SOCIETY
·
2023
·
IF 5.7
Zhenxiao Tang,Yuanming Zhou,Ruizhi Liu,Maozhong Yi,Ke Peng
The preparation of a ZrB 2 -SiC coating-matrix integrated C/C composite was achieved by a slurry method and precursor infiltration and pyrolysis. The obtained composites consisted of a SiC outer layer, a ZrB 2 -SiC inner layer and a C/C-ZrB 2 -SiC substrate. Compared with a composite without the ZrB 2 -SiC layer, the mass ablation rates of the composite were reduced by 14.8 %, 12.0 %, and 19.4 %, and the linear ablation rates were reduced by 41.3 %, 28.2 %, and 14 %, respectively, after ablation under an oxyacetylene flame with a heat flux of 4.18 MW/m 2 for 60 s, 120 s, and 300 s. During the ablation process, the SiC outer layer played a role in reducing the heating rate and surface temperature and promoting the sintering of ZrO 2 so that the oxide layer avoided peeling off under large thermal stress. The ZrB 2 -SiC inner layer acted as an oxygen, heat and flow barrier, reducing the oxidation rate of the substrate.
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高影响因子
APPLIED SURFACE SCIENCE
·
2018
·
IF 4.439
Ji Ying Long,Zhi Shuo Yan,Yun Gong,Jian Hua Lin
Based on a meta-organic framework (MOF) formulated as [Co 4 (phen) 4 Cl 8 ] (phen = 1, 10-phenanthroline) as precursor, Cl/O doped C/CoO material (C/CoO-200) was synthesized by a one-step calcining method at a low temperature of 200 °C. In C/CoO-200, CoO nanoparticles with an average size of 25 nm were linked by carbon matrix into particles with the diameter of 200 nm ∼ 1 μm. The sample possessed a very low atomic percentage of CoO (CoO: 1.9%; C: 86.8%) due to the large amount of carbon from the organic ligand, phen in the precursor. However, it still exhibited a large specific capacitance of 1052 F g −1 at 0.5 A g −1 in 2 M KOH electrolyte with a 79.6% capacitance retention at 10 A g −1 . After successive etched in acid, Cl/O doped carbon nanoparticles were obtained. C-300 was composed by individual nanoparticles with size of 100–500 nm, it showed a specific capacitance of 207 and 164 F g −1 in 2 M KOH at a current density of 0.5 and 1 A g −1 , respectively, which was comparable to the commercial activated carbon (AC) (199 and 179 F g −1 for AC at 0.5 and 1 A g −1 , respectively). An asymmetric supercapacitor based on the positive electrode of C/CoO-200 and the negative electrode of C-300 exhibited a stable performance with a 61% retention of specific capacitance after 10,000 charging-discharging cycles at 1.5 A g −1 .
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高影响因子
ISIJ INTERNATIONAL
·
2017
·Vol. 57
·期 1
·62-67
·
IF 1.11
Zijian Su,Yuanbo Zhang,Yingming Chen,Guanghui Li,Tao Jiang
A considerable amount of works were focused on the formation mechanism of calcium ferrite phases during the iron ore sintering process, especially under various O2 content atmospheres at temperatures higher than 1100°C. But little attention has been paid on reactions between CaO and iron oxides in CO–CO2 atmospheres at lower temperatures. In this study, the solid state reaction mechanisms between CaO and Fe3O4 under CO–CO2 atmospheres at 800°C–1100°C were revealed by using XRD, VSM, etc. The results indicated that Ca2Fe2O5 was easily formed under 5–50 vol% CO/(CO+CO2) atmosphere above 850°C via the reaction of 6CaO + 2Fe3O4 +CO2 = 3Ca2Fe2O5 + CO and the reaction would be promoted with increasing the roasting temperature. In the CO–CO2 atmosphere, Fe3O4 is easily oxidized to Fe2O3 in the presence of CaO because CO2 components act as oxidative medium for the oxidation of Fe2+ to Fe3+.
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高影响因子
MONATSHEFTE FUR CHEMIE
·
2014
·Vol. 145
·期 12
·1925-1931
·
IF 1.347
Tu Xingzhao,Zhou Lihong,Li Zhijie,Lei Ning,Zeng Qingle
Abstract The carbon-heteroatom bond formation is an important research field. Transition-metal-free synthesis of medicinally important heterocycles avoids products of transition metal contamination, and thus it is an environmentally friendly and cost-saving process. A transition-metal-free domino C-S/C-N formation for the synthesis of imidazobenzothiazines from 2-mercaptobenzimidazoles and 2-halobenzyl bromides is developed. The desired products were obtained in good to excellent yields. The mechanism of domino nucleophilic substitution (S N 2) and nucleophilic aromatic substitution (S N Ar) is proposed. Graphical abstract
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高影响因子
Catalysis Science & Technology
·
2024
·Vol. 14
·期 4
·973-979
·
IF 4.4
Peidong Ren,Lei Shi,Ziwang Kan,Jiaxiao Bai,Yunyi Liu,Shucheng Yang,Siqi Li,Song Liu
The electrochemical conversion of lignin for the production of high-value aromatic compounds holds immense potential. However, the process of depolymerizing lignin faces significant challenges due to its intricate structure, particularly the existence of C–C bonds, resulting in low conversion and product yields. In this work, we report the successful synthesis of a molecular palladium catalyst and its inaugural application in the electrochemical conversion of lignin model compounds. This catalyst with well-defined coordination structure demonstrates exceptional efficacy and achieves a remarkable 99% conversion rate for the lignin model compound 2-phenoxy-1-phenylethanol with a yield of 32% of the benzaldehyde product while valuable hydrogen is produced at the electrode under ambient conditions. Furthermore, employing radical trapping and EPR test point that the tBuO˙ radical was the key to inducing C–C cleavage for high conversion and enabled a comprehensive elucidation of the possible reaction pathways involving radical/radical cross-coupling. Based on this study, we believe that molecular catalysts will open a new chapter in the electrocatalytic conversion of lignin.
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高影响因子
ACS Sustainable Chemistry & Engineering
·
2019
·
IF 6.97
Wenwen Qiang,Xiang Liu,Teck-Peng Loh
The first example of a heterogeneous catalyst based on hydrotalcite-derived Mg–Al oxides supported iridium (Ir/MgxAlO) for activation of methanol in the synthesis of bis(indolyl)methanes (BIMs) is reported. In this clean and reusable iridium-based catalytic system, a variety of substituted indoles were selectively converted to their corresponding BIMs in moderate to good yields with high tolerance to reducible functional groups by using methanol as a bridging methylene (−CH2−) donor. The high catalytic activity and selectivity of the reaction benefit from the delicate cooperation of redox/acid–base surface sites on this artificially designed multifunctional Ir/MgxAlO catalyst. The overall simplicity, chemoselectivity and sustainability of the catalytic system make this approach a valuable and step-economical tool to construct C–C bond directly from methanol in the synthesis of more complex molecules.
研究领域:
化学
·
催化材料科学
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CHEMICAL ENGINEERING JOURNAL
·
2025
·
IF 13.2
Yun Tang,Jingqi Ruan,Yalou Xin,Xiaohu Ren,Hudie Yuan,Xianhu Liu,Qiang Chen
The development of metal–organic frameworks (MOFs)-derived magnetic carbon-based materials for high-efficiency electromagnetic wave (EMW) absorption has attracted widespread attention. While these MOFs-derived composites have shown exceptional performance in absorbing EMWs within the X and Ku bands, the pursuit of effective absorption at lower frequencies remains a challenge. Herein, we demonstrate a novel strategy to synthesize hollow Co@C/C rods with excellent C-band EMW absorption via acetic acid etching and pyrolysis of core–shell ZIF-8@ZIF-67. Based on acetic acid etching, ligand-deficient ZIF-8@ZIF-67 rods with abundant mesoporous structures are constructed, enabling precise control over the Co nanoparticles content, graphitization degree, and pyridinic N doping in the derived Co@C/C. This simple fine-tuning approach simultaneously reduces dipole polarization by lowering the pyridinic N doping concentration, suppresses interfacial polarization and conduction loss through reducing the number of graphitic carbon layer, and enhances magnetic loss by increasing the Co content. These combined effects collectively improve the impedance matching of Co@C/C for low-frequency absorption. Notably, as the volume of acetic acid solution increases, the absorption frequency band of Co@C/C gradually shifts from the Ku-band to the C-band, while sustaining superior EMW absorption performance. At the filling ratio of merely 11 %, the RL min values for Co@C/C-20 and Co@C/C-30 achieve −49.8 dB and −34.7 dB at 7.2 GHz and 6.8 GHz, respectively. This study offers a valuable approach to the development of lightweight materials with excellent EMW absorption in C-band.
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