Reaction coupling preparation of high sintering activity boron carbide nano-powders

Large scale B₄C nano-powders were synthesized via a novel ball milling assisted reaction coupling self-propagating high temperature synthesis method using Mg, B₂O₃ and CH₂H₃Cl as the starting materials. The XRD, FTIR, Raman, EDX, FSEM, TEM, HRTEM and SAED were used to characterize the B₄C samples. The optimum endothermic rate was 35%, when the samples presented fine and uniform regular morphology with an average particle diameter of about 100 nm. In addition, the reaction coupling principle, possible chemical reaction mechanism and the effects of the endothermic reaction rate were also discussed. Moreover, the commercial B₄C (C-B₄C) and homemade B₄C (H-B₄C) ceramics were prepared by spark-plasma sintering method at 1700 °C under 30 Mpa. Compared with the C-B₄C ceramic, the values of relative density, vickers hardness and fracture toughness of the H-B₄C ceramic were increased by 2.1%, 9.2% and 20.1%, respectively, demonstrating high sintering activity of the homemade B₄C nano-powders.     

A Note on the Effect of Microwave Heating on Iodine-Catalyzed Acetylation of Wood

The effect of microwave heating on the iodine-catalyzed acetylation of rubberwood with acetic anhydride has been investigated. Microwave radiation was used as the heating source for modifying specimens saturated with acetic anhydride in bulk solution (excess of reagent) and impregnated specimens (limited supply of anhydride). Extent of modification of wood was expressed in terms of weight percent gain (WPG) and modification was characterized using FTIR spectroscopy. In bulk solution, microwave radiations were primarily absorbed by anhydride solutions for heating purposes and a moderate WPG was obtained. However, when microwave heating was used to modify impregnated wood specimens under no excess of anhydride, a significant enhancement in degree of modification was achieved within a few minutes. The modified wood exhibited good anti-swelling efficiency.     

综述与展望 丙烷直接氨氧化制丙烯腈生产工艺及催化剂研究进展

概述丙烯腈的生产方法及特点,分析丙烷直接氨氧化生产丙烯腈的工艺特点和优势,对丙烷直接制备丙烯腈的催化剂体系Sb-V-O催化剂、Mo-V-Te-Nb-O催化剂、钒-铝氮氧化物及分子筛类催化剂等进行介绍,并建议我国尽快实现以丙烷为原料生产丙烯腈。     

Roll bonding of AA5052 and polypropylene sheets: Bonding mechanisms,microstructure and mechanical properties

Structural, microstructural and mechanical properties in roll bonding of AA5052 and polypropylene sheets have been evaluated in this study. The surface roughness of the AA5052 sheets, rolling temperature and the surface energy of polymer were selected as the bonding variables. The findings indicated that an increase in the surface energy of polypropylene by grafting maleic anhydride would result in higher bonding strength due to chemical interaction between the AA5052 and the maleic anhydride grafted polypropylene (PP-g-MAH). In fact, this reaction caused the formation of an interphase layer at the polymer side of the interface and the diffusion of aluminum into the PP-g-MAH layer. It was also observed that an increase in the rolling temperature increases bonding strength because the polymer penetrates the AA5052 surface irregularities more easily, the PP-g-MAH molecules move more smoothly toward the AA5052 surface, and finally there are more chemical interactions among the layers. An Increase in the bonding strength through increasing the AA5052 surface roughness was attributed to an increase of the van der Waals force and more interaction surface among the layers along with higher mechanical interlocking in the shear tension test.     

High Hole Mobility of GaSb Relaxed Epilayer Grown on GaAs Substrate by MOCVD through Interfacial Misfit Dislocations Array

The structural property of GaSb epilayers grown on semi-insulator GaAs (001) substrate by metalorganic chemical vapor deposition (MOCVD) using Triethylgallium (TEGa) and trimethylantimony (TMSb),was investigated by variation of the Sb:Ga (V/III) ratio.An optimum V/III ratio of 1.4 was determined in our growth conditions.Using transmission electron microscopy (TEM),we found that there was an interfacial misfit dislocations (IMF) growth mode in our experiment,in which the large misfit strain between epilayer and substrate is relaxed by periodic 90 deg.IMF array at the hetero-epitaxial interface.The rms roughness of a 300 nm-thick GaSb layer is only 2.7 nm in a 10 μm×10 μm scan from atomic force microscopy (AFM) result.The best hole density and mobility of 300 nm GaSb epilayer are 5.27×10 6 cm 3 (1.20×10 6) and 553 cm 2 ·V 1 ·s 1 (2340) at RT (77 K) from Hall measurement,respectively.These results indicate that the IMF growth mode can be used in MOCVD epitaxial technology similar to molecular beam epitaxy (MBE) technology to produce the thinner GaSb layer with low density of dislocations and other defects on GaAs substrate for the application of devices.     

Chemical composition,antioxidative capacity and interactive antimicrobial potency of Satureja khuzestanica Jamzad essential oil and antimicrobial agents against selected food‐related microorganisms

This study aimed to determine the chemical composition, antimicrobial and antioxidative activity of Satureja khuzestanica Jamzad essential oil. The oil was analysed by GC and GC/MS. Twenty‐eight constituents were identified. The oxygenated monoterpenes (78.22%) were the principal compound group. Among them, carvacrol (53.86%) and thymol (19.84%) were the most abundant constituents. The oil exhibited an acceptable antimicrobial activity against most of the tested microorganisms. The checkerboard method was applied to determine fractional inhibitory concentration indices (FICIs) to interpret the synergetic, additive, indifference or antagonistic interactions between essential oil and each of antimicrobials (lysozyme, ciprofloxacin, fluconazole and amphotericin B) against food‐related microorganisms. The synergetic phenomenon (FICI ≤ 0.5) was observed in majority of combinations with the exception of the essential oil and lysozyme. The oil exhibited good 1,1‐diphenyl‐2‐picrylhydrazyl radical scavenging activity (IC₅₀ = 28.71 μg mL^?1). Also, the oil had strong antioxidative activity in β‐carotene‐linoleic acid assay relative antioxidant activity (RAA% = 95.45). This study demonstrated that the essential oil has beneficial biological properties and its simultaneous application with standard antimicrobials against food‐related microorganisms result in reduction in inhibitory doses of the antimicrobials in vitro.     

A new wide area information based power system out-of-step oscillation detecting and oscillation center tracking scheme

A new out-of-step oscillation detecting and oscillation center tracking scheme based on the wide area information obtained from phasor measurement units (PMU) is proposed in this paper. In this scheme, the out-of-step oscillation is detected by the change rate of phase angle difference between bus voltage and system current, and the oscillation center tracking is completed by analyzing the phase angle relation between terminal bus voltages of electrical components and the system current. The scheme is easy to implement, and the tracking result is not affected by the changes of system structure and operation modes. Even in the complicated situations that the impedances of the whole system are nonuniform and the equivalent system potential amplitudes are not equal, it can still work well. The simulation results on PSCAD prove it is efficient. Utilizing the tracking results, a new out-of-step splitting criterion is given with which the splitting section can be determined dynamically according to the real-time operation state of power system.     

Degradation mechanisms in Li‐ion batteries: a state‐of‐the‐art review

One of the most prominent energy storage technologies which are under continuous development, especially for mobile applications, is the Li‐ion batteries due to their superior gravimetric and volumetric energy density. However, limited cycle life of Li‐ion batteries inhibits their extended use in stationary energy storage applications. To enable wider market penetration of Li‐ion batteries, detailed understanding of the degradation mechanisms is required. A typical Li‐ion battery comprised of an active material, binder, separator, current collector, and electrolyte, and the interaction between these components plays a critical role in successful operation of such batteries. Degradation of Li‐ion batteries can have both chemical and mechanical origins and manifests itself by capacity loss, power fading or both. Mechanical degradation mechanisms are associated with the volume changes and stress generated during repetitive intercalation of Li ions into the active material, whereas chemical degradation mechanisms are associated with the parasitic side reactions such as solid electrolyte interphase formation, electrolyte decomposition/reduction and active material dissolution. In this study, the main degradation mechanisms in Li‐ion batteries are reviewed. Copyright © 2017 John Wiley & Sons, Ltd.