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991.
Petr Brázda Eva Večerníková Eva Pližingrová Adriana Lančok Daniel Nižňanský 《Journal of Thermal Analysis and Calorimetry》2014,117(1):85-91
Thermal behavior of highly crystalline ε-Fe2O3 nanoparticles of different apparent crystallite sizes was characterized using thermogravimetry, differential thermal analysis, and analysis of evolved gas by mass spectrometry. Phase composition of the samples was monitored ex situ by X-ray powder diffraction. The results show that the thermal stability of this metastable iron oxide polymorph decreases with increasing particle size. For the particle diameter of 19(2) nm, the transformation temperature was equal to 794(5) °C, while for 28(2) nm only 755(10) °C. Surface of the nanoparticles contained adsorbed water and carbon dioxide. Elimination of these species proceeds in two steps. Water is removed at temperatures below 200 °C and CO2 in the temperature range between 200 and 450 °C. 相似文献
992.
Lan Yu Hui Ren Xue-yong Guo Xia-bing Jiang Qing-jie Jiao 《Journal of Thermal Analysis and Calorimetry》2014,117(3):1187-1199
A novel ε-HNIW-based explosive formula with low sensitive and high energy was developed by systematically researching the processes of recrystallization, granularity gradation, and coating of ε-HNIW and option of energetic deterrents. The grain size and morphology of HNIW crystals were modified by solvent/antisolvent recrystallization. The ε-HNIW particles were graded and coated by emulsion polymerization method with 551 glue. The binder reduced the mechanical sensitivity of ε-HNIW significantly and showed good compatibility with ε-HNIW, but also weakened the decomposition enthalpy. With the purpose of developing new energetic deterrents in insensitive high explosive formulations, novel carbon materials graphene oxide (GO) and reduced graphene oxide (rGO) were prepared and incorporated in plastic-bonded explosive (PBX) formulations. For comparison, the effects of conventional deterrent flake graphite were also involved. It turned out that the mechanical sensitivities of ε-HNIW/551 glue have all reduced to some extent with the incorporation of graphite, GO, and rGO. Flake graphite induced the PBX decompose earlier slightly and weaken the heat output. The addition of GO resulted in noticeable antedating decomposition of ε-HNIW/551 glue although remarkably increased the decomposition heat. The formula of ε-HNIW/551 glue/rGO provided a moderate growth in decomposition heat and best thermal stability. In slow cook-off tests, the formulas of ε-HNIW/551 glue and ε-HNIW/551 glue/rGO showed good thermal stability and might be qualified to apply safely under 200 °C. Comprehensively considering the mechanical sensitivity, thermals stability, energy performance, and practical application, ε-HNIW/551 glue/rGO is supposed to be an eligible insensitive high-energy PBX formula. 相似文献
993.
Dongrui Chen Benzhen Li Youhao Liao Hongwei Lan Haibin Lin Lidan Xing Yating Wang Weishan Li 《Journal of Solid State Electrochemistry》2014,18(7):2027-2033
Three samples, LiNi0.5Mn1.5O4, LiNi0.4Mn1.4Co0.2O4, and LiNi0.4Mn1.4Cr0.15Co0.05O4, were prepared by sol–gel method and characterized by powder X-ray diffraction, Fourier transformed infrared spectroscope, scanning electron microscopy, Brunauer–Emmett–Teller surface area, four-probe resistance, cyclic voltammetry, electrochemical impedance spectroscopy, and charge–discharge test. It is found that the co-doped sample LiNi0.4Mn1.4Cr0.15Co0.05O4 exhibits an improved performance compared with the Co-doped sample LiNi0.4Mn1.4Co0.2O4 and the undoped sample LiNi0.5Mn1.5O4, especially at elevated temperature. At 25 °C, the discharge capacity of LiNi0.4Mn1.4Cr0.15Co0.05O4 is 130 mAh g?1 at 0.1 C and 103 mAh g?1 at 10 C. At an elevated temperature (55 °C), its 1 C discharge capacity is 136 mAh g?1 and maintains 95.6 % of its initial capacity after 100 cycles. Compared with the reported results of LiNi0.4Mn1.4Co0.2O4 and LiNi0.475Mn1.475Co0.05O4, the co-doped sample LiNi0.4Mn1.4Cr0.15Co0.05O4, with least content of Co, 0.05, possesses not only the high C-rate capacity but also the structural stability. The mechanism on the electrochemical performance improvement of LiNi0.5Mn1.5O4 by the co-doping was discussed. 相似文献
994.
Guishan Zou Xiukang Yang Xianyou Wang Long Ge Hongbo Shu Yansong Bai Chun Wu Haipeng Guo Liang Hu Xin Yi Bowei Ju Hai Hu Di Wang Ruizhi Yu 《Journal of Solid State Electrochemistry》2014,18(7):1789-1797
The Li-rich Li1.3[Ni0.35Mn0.65]O2+x microspheres are firstly prepared and subsequently transferred into the Al2O3-coated Li-rich Li1.3[Ni0.35Mn0.65]O2+x microspheres by a simple deposition method. The as-prepared samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge/discharge tests. The results reveal that the Al2O3-coated Li-rich Li1.3[Ni0.35Mn0.65]O2+x sample has a typical α-NaFeO2 layered structure with the existence of Li2MnO3-type integrated component, and the Al2O3 layer is uniformly coated on the surface of the spherical Li-rich Li1.3[Ni0.35Mn0.65]O2+x particles with a thickness of about 4 nm. Importantly, the Al2O3-coated Li-rich sample exhibits obviously improved electrochemical performance compared with the pristine one, especially the 2 wt.% Al2O3-coated sample shows the best electrochemical properties, which delivers an initial discharge capacity of 228 mAh g?1 at a rate of 0.1 C in the voltage of 2.0–4.6 V, and the first coulombic efficiency is up to 90 %. Furthermore, the 2 wt.% Al2O3-coated sample represents excellent cycling stability with capacity retention of 90.9 % at 0.33 C after 100 cycles, much higher than that of the pristine one (62.2 %). Particularly, herein, the typical inferior rate capability of Li-rich layered cathode is apparently improved, and the 2 wt.% Al2O3-coated sample also shows a high rate capability, which can deliver a capacity of 101 mAh g?1 even at 10 C. Besides, the thin Al2O3 layer can reduce the charge transfer resistance and stabilize the surface structure of active material during cycling, which is responsible for the improvement of electrochemical performance of the Li-rich Li1.3[Ni0.35Mn0.65]O2+x . 相似文献
995.
Lan Liu Ruisong Guo Chao Wang Chao Zhang Yuexia Yang Shanshan Wang 《Journal of Solid State Electrochemistry》2014,18(10):2771-2779
Nickel-substituted layered perovskite PrBaCo2 ? x Ni x O5 + δ (PBCN) powders with various proportions of nickel (x?=?0, 0.1, 0.2, and 0.3, abbreviated as PBCN-0, PBCN-1, PBCN-2, and PBCN-3, respectively) are investigated as potential cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) based on the yttria-stabilized zirconia (YSZ) electrolyte. It is found that PBCN-1 has the highest electrical conductivity of 1,397 S cm?1 at 400 °C. Substitution of Co by Ni decreases the thermal expansion coefficient (TEC) clearly. The average TEC at the temperature range of 35–900 °C decreases from 22.8?×?10?6 K?1 for PBCN-0 to 18.9?×?10?6 K?1 for PBCN-3. The polarization resistances of PBCN samples on YSZ electrolyte at 800 °C are 0.053, 0.048, 0.052, and 0.042 Ω cm2 for PBCN-0, PBCN-1, PBCN-2, and PBCN-3, respectively. The single fuel cell with the configuration of PBCN-3/YSZ/Pt delivers the highest power densities of 100, 185, 360, 495, and 660 mW cm?2 at 600, 650, 700, 750, and 800 °C, respectively. 相似文献
996.
Biosynthesis of Streptolidine Involved Two Unexpected Intermediates Produced by a Dihydroxylase and a Cyclase through Unusual Mechanisms
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Dr. Chin‐Yuan Chang Syue‐Yi Lyu Dr. Yu‐Chen Liu Ning‐Shian Hsu Dr. Chih‐Chung Wu Dr. Cheng‐Fong Tang Kuan‐Hung Lin Dr. Jin‐Yuan Ho Dr. Chang‐Jer Wu Dr. Ming‐Daw Tsai Dr. Tsung‐Lin Li 《Angewandte Chemie (International ed. in English)》2014,53(7):1943-1948
Streptothricin‐F (STT‐F), one of the early‐discovered antibiotics, consists of three components, a β‐lysine homopolymer, an aminosugar D ‐gulosamine, and an unusual bicyclic streptolidine. The biosynthesis of streptolidine is a long‐lasting but unresolved puzzle. Herein, a combination of genetic/biochemical/structural approaches was used to unravel this problem. The STT gene cluster was first sequenced from a Streptomyces variant BCRC 12163, wherein two gene products OrfP and OrfR were characterized in vitro to be a dihydroxylase and a cyclase, respectively. Thirteen high‐resolution crystal structures for both enzymes in different reaction intermediate states were snapshotted to help elucidate their catalytic mechanisms. OrfP catalyzes an FeII‐dependent double hydroxylation reaction converting L ‐Arg into (3R,4R)‐(OH)2‐L ‐Arg via (3S)‐OH‐L ‐Arg, while OrfR catalyzes an unusual PLP‐dependent elimination/addition reaction cyclizing (3R,4R)‐(OH)2‐L ‐Arg to the six‐membered (4R)‐OH‐capreomycidine. The biosynthetic mystery finally comes to light as the latter product was incorporation into STT‐F by a feeding experiment. 相似文献
997.
Spectroscopic and Computational Study of a Nonheme Iron Nitrosyl Center in a Biosynthetic Model of Nitric Oxide Reductase
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Dr. Saumen Chakraborty Julian Reed Matthew Ross Dr. Mark J. Nilges Igor D. Petrik Dr. Soumya Ghosh Prof. Dr. Sharon Hammes‐Schiffer Prof. Dr. J. Timothy Sage Prof. Dr. Yong Zhang Prof. Dr. Charles E. Schulz Prof. Dr. Yi Lu 《Angewandte Chemie (International ed. in English)》2014,53(9):2417-2421
A major barrier to understanding the mechanism of nitric oxide reductases (NORs) is the lack of a selective probe of NO binding to the nonheme FeB center. By replacing the heme in a biosynthetic model of NORs, which structurally and functionally mimics NORs, with isostructural ZnPP, the electronic structure and functional properties of the FeB nitrosyl complex was probed. This approach allowed observation of the first S=3/2 nonheme {FeNO}7 complex in a protein‐based model system of NOR. Detailed spectroscopic and computational studies show that the electronic state of the {FeNO}7 complex is best described as a high spin ferrous iron (S=2) antiferromagnetically coupled to an NO radical (S= 1/2) [Fe2+‐NO.]. The radical nature of the FeB‐bound NO would facilitate N? N bond formation by radical coupling with the heme‐bound NO. This finding, therefore, supports the proposed trans mechanism of NO reduction by NORs. 相似文献
998.
Candy Haley Yi Xuan Lim Milos Nesladek Prof. Kian Ping Loh 《Angewandte Chemie (International ed. in English)》2014,53(1):215-219
Using IR spectroscopy, high‐pressure reactions of molecules were observed in liquids entrapped by graphene nanobubbles formed at the graphene–diamond interface. Nanobubbles formed on graphene as a result of thermally induced bonding of its edges with diamond are highly impermeable, thus providing a good sealing of solvents within. Owing to the optical transparency of graphene and diamond, high‐pressure chemical reactions within the bubbles can be probed with vibrational spectroscopy. By monitoring the conformational changes of pressure‐sensitive molecules, the pressure within the nanobubble can be calibrated as a function of temperature and it is about 1 GPa at 600 K. The polymerization of buckministerfullerene (C60), which is symmetrically forbidden under ambient conditions, is observed to proceed in well‐defined stages in the pressurized nanobubbles. 相似文献
999.
Photochemically Engineering the Metal–Semiconductor Interface for Room‐Temperature Transfer Hydrogenation of Nitroarenes with Formic Acid
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Dr. Xin‐Hao Li Yi‐Yu Cai Ling‐Hong Gong Dr. Wei Fu Dr. Kai‐Xue Wang Dr. Hong‐Liang Bao Dr. Xiao Wei Dr. Jie‐Sheng Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(50):16732-16737
A mild photochemical approach was applied to construct highly coupled metal–semiconductor dyads, which were found to efficiently facilitate the hydrogenation of nitrobenzene. Aniline was produced in excellent yield (>99 %, TOF: 1183) using formic acid as hydrogen source and water as solvent at room temperature. This general and green catalytic process is applicable to a wide range of nitroarenes without the involvement of high‐pressure gases or sacrificial additives. 相似文献
1000.
Dr. Valentine K. Johns Dr. Ping Peng Joseph DeJesus Zhuozhi Wang Dr. Yi Liao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(3):689-692
A new photoacid that reversibly changes from a weak to a strong acid under visible light was designed and synthesized. Irradiation generated a metastable state with high C?H acidity due to high stability of a trifluoromethyl‐phenyl‐tricyano‐furan (CF3PhTCF) carbanion. This long‐lived metastable state allows a large proton concentration to be reversibly produced with moderate light intensity. Reversible pH change of about one unit was demonstrated by using a 0.1 mM solution of the photoacid in 95 % ethanol. The quantum yield was calculated to be as high as 0.24. Kinetics of the reverse process can be fitted well to a second‐order‐rate equation with k=9.78×102 M ?1 s?1. Response to visible light, high quantum yield, good reversibility, large photoinduced proton concentration under moderate light intensity, and good compatibility with organic media make this photoacid a promising material for macroscopic control of proton‐transfer processes in organic systems. 相似文献