Evaluating the Thermal Hazard of Double-Base Propellant SQ-2 by Using Microcalorimetry Method

The thermal decomposition behavior of double‐base rocket propellant SQ‐2 was studied by a Calvet microcalorimeter at four different heating rates. The kinetic and thermodynamic parameters were obtained from the analysis of the heat flow curves. The critical temperature of thermal explosion (T_b), the self acceleration decomposition temperature (T_SADT), the adiabatic decomposition temperature rise (ΔT_ad), the time‐to‐explosion of adiabatic system (t), critical temperature of hot‐spot initiation (T_cr), critical thermal explosion ambient temperature (T_acr), safety degree (SD) and thermal explosive probability (P_TE) were presented to evaluate the thermal hazard of SQ‐2.     

Highly Efficient Oxidative Bromination of Alkanes with the HBr-H2O2 System in the Presence of Catalyst

Various cycloalkanes and straight‐chain alkanes were efficiently brominated with an aqueous HBr‐H₂O₂ system. This oxidative brominating process was promoted by catalysis and irradiation with light. The cycloalkanes were converted to the corresponding bromo‐cycloalkanes in moderate yields and the straight‐chain alkanes produced dominantly secondary bromides. This simple but effective bromination method of alkanes is characterized by high atom efficiency, inexpensive reagents and the absence of organic waste, which make it a good alternative to the existing method for C? H activation through bromination.     

pH-Dependent Assembly of Two Novel Organic–inorganic Hybrids Based on Vanadoantimonate Clusters

Two novel organic–inorganic hybrid vanadoantimonate compounds, [Zn₂(dien)₃][{Zn(dien)}₂V₁₆Sb₄O₄₂(H₂O)]·4H₂O (1) and [Zn(dien)₂]₂ [{Zn(dien)}₂(V₁₄Sb₈O₄₂)₂(H₂O)]·4H₂O (2) (dien = Diethylenetriamine), have been synthesized hydrothermally at different pH value, and structurally characterized by elemental analyses, FT-IR, XPS, TGA and single crystal X-ray diffraction analysis. Compound 1 is composed of the rare [V₁₆Sb₄O₄₂]⁸⁻ cluster covalently linked by two [Zn(dien)]²⁺ coordination cations to yield a novel one-dimensional linear chain. Compound 2 exhibits a one-dimensional zigzag chain constructed from the [V₁₄Sb₈O₄₂]⁴⁻ cluster and [Zn(dien)]²⁺ coordination polymer. The two examples represent the first one-dimensional assemblies based on vanadoantimonate cluster and the metal–organic complex moieties.     

Experimental study of infrared nanosecond laser ablation of silicon: The multi-pulse enhancement effect

Experimental study has been performed on nanosecond (ns) laser ablation of silicon at 1064 nm, through which a so-called “multi-pulse enhancement effect” has been revealed, which has been rarely reported in literature. The major features of this effect are: (1) for multi-pulse laser ablation at the same spatial location, the ablation efficiency increases as the pulse number increases and the pulse-to-pulse temporal distance decreases; (2) for multi-pulse ablation performed sequentially at a group of locations, the ablation quality and efficiency starting from the second location can be significantly enhanced if the distance between adjacent locations is sufficiently small. Further study is needed to confirm and understand the underlying physical mechanism for the multi-pulse enhancement effect, which can be utilized to significantly improve the quality and efficiency of laser silicon micromachining using the low-cost and low-energy-consumption infrared ns lasers. This may decrease the cost and energy consumption of many relevant areas, such as the solar cell industry.     

Solution-combusting preparation of mono-dispersed Mn3O4 nanoparticles for electrochemical applications

Manganese oxide (Mn₃O₄) nanoparticles with average diameter of 15 nm were prepared using alcohol solution of manganese chloride as starting material via a facile solution-combusting method. The flame core zone was chosen to prepare mono-dispersed and high crystalline products, which were employed to modify glassy carbon electrode and detect dopamine via cyclic voltammetry. The results exhibited excellent electrochemical sensitivity. A linear relationship between the concentration of dopamine and its oxidation peak current was obtained by differential pulse voltammetry, which will find wide application in the biological detection.     

Bis(β‐ketoamino)copper(II)/methylaluminoxane systems for homo‐ and copolymerizations of methyl acrylate and 1‐hexene

Two bis(β‐ketoamino)copper [ArNC(CH₃)CHC(CH₃)O]₂Cu ( 1 , Ar = 2,6‐dimethylphenyl; 2 , Ar = 2,6‐diisopropylphenyl) complexes were synthesized and characterized. Homo‐ and copolymerizations of methyl acrylate (MA) and 1‐hexene with bis(β‐ketoamino)copper(II) complexes activated with methylaluminoxane (MAO) were investigated in detail. MA was polymerized in high conversion (>72%) to produce the syndio‐rich atactic poly(methyl acrylate), but 1‐hexene was not polymerized with copper complexes/MAO. Copolymerizations of MA and 1‐hexene with 1 , 2 /MAO produced acrylate‐enriched copolymers (MA > 80%) with isolated hexenes in the backbone. The calculation of reactivity ratios showed that r(MA) is 8.47 and r(hexene) is near to 0 determined by a Fineman‐Ross method. The polymerization mechanism was discussed, and an insertion‐triggered radical mechanism was also proposed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1113–1121, 2010     

3D visualization of the microstructure of Quedius beesoni Cameron using micro-CT

The investigation of the internal morphology of insects is usually performed using classical microtomy yielding optical micrographs of stained thin sections. The achievement of high-quality cross sections for microtomy is time-consuming and the risk of damaging sections is unavoidable. Moreover, the approach is impractical, in particular when quick acquisition of 3D structural information is required. Recently, X-ray computed microtomography (micro-CT) with a high spatial resolution was considered as a potential tool for the morphological classification of insects. We used micro-CT to investigate Quedius beesoni Cameron at the cellular length scale. This method provides a new powerful and nondestructive approach to obtain 3D structural information on the biological organization of insects. The preliminary images presented in this contribution clearly reveal the endoskeleton and the muscles of the head and the thorax with a full 3D structure. We also reconstructed the 3D structure of the brain of Quedius beesoni Cameron, and this is the first reconstruction in Staphylinidae, which will be a great advancement for morphological and phylogenic research. We claim that both the spatial resolution and the contrast characteristic of micro-CT imaging may fulfill the requirements necessary for zoological insect morphology and phylogeny, in particular, when a classification of a rare and unique insect specimen is required.     

Densification mechanism of polyacrylonitrile-based carbon fiber during heat treatment

Polyacrylonitrile (PAN)-based carbon fibers were heat treated at various temperatures for varying durations to simulate the graphitization process in the manufacture of C/C composites. Densification of the resulting fibers was confirmed by density measurement. The composition and structure of the fibers were investigated by means of elemental analysis, X-ray diffraction and Raman spectroscopy. For specified isothermal heat treatment time, the structural parameters depended strongly on heat treatment temperature. The nitrogen content decreased with increased heat treatment temperature and extended time at constant temperature. Nitrogen loss was complete at temperatures above 1900 °C. The graphite crystallite size increased rapidly with increasing heat treatment temperature, and slowly with extended isothermal heat treatment time. At 2100 °C a more ordered graphitic structure appeared. Denitrogenation induced “puffing”, which made the fibers expand. Decrease in density in the heat treatment temperature range 1500-1900 °C originated from the abrupt evolution of nitrogen, and above 1900 °C the graphitization transition induced steadily increasing density. Densification of the carbon fibers was determined both by the rate of denitrogenation and the rearrangement of carbon atoms.