Pressure‐Induced Structural Transition in WO3 Nanowires

Raman spectroscopic analysis is performed on WO₃ nanowires at room temperature at pressures from ambient conditions to 45 GPa. Linear dependence of the first‐order Raman signal on various high‐pressure (HP) sections is observed. Upon increasing the applied pressure, the WO₃ nanowires undergo four phase transitions at pressures around 1.7, 4.6, 21.5, and 26.2 GPa, which are all less than that reported for bulk WO₃. When the pressure is up to 42.5 GPa, a new high‐pressure phase (HP5) appears. This phase has never been reported and is not reversible while unloading the pressure.     

Decomposition of 1,1‐dimethyl‐1‐silacyclobutane on a tungsten filament—evidence of both ring C?C and ring Si?C bond cleavages

The decomposition of 1,1‐dimethyl‐1‐silacyclobutane (DMSCB) on a heated tungsten filament has been studied using vacuum ultraviolet laser single photon ionization time‐of‐flight mass spectrometry. It is found that the decomposition of DMSCB on the W filament to form ethene and 1,1‐dimethylsilene is a catalytic process. In addition, two other decomposition channels exist to produce methyl radicals via the Si? CH₃ bond cleavage and to form propene (or cyclopropane)/dimethylsilylene. It has been demonstrated that both the formation of ethene and that of propene are stepwise processes initiated by the cleavage of a ring C? C bond and a ring Si? C bond, respectively, to form diradical intermediates, followed by the breaking of the remaining central bonds in the diradicals. The formation of ethene via an initial cleavage of a ring C? C bond is dominant over that of propene via an initial cleavage of a ring Si? C bond. When the collision‐free condition is voided, secondary reactions in the gas‐phase produce various methyl‐substituted 1,3‐disilacyclobutane molecules. The dominant of all is found to be 1,1,3,3‐tetramethyl‐1,3‐disilacyclobutane originated from the dimerization of 1,1‐dimethylsilene. Copyright © 2010 John Wiley & Sons, Ltd.     

Towards the Accurate Calculation of 183W NMR Chemical Shifts in Polyoxometalates: The Relevance of the Structure

DFT calculations were carried out to study ¹⁸³W NMR chemical shifts in the family of the Keggin anions with formula α‐[XW₁₂O₄₀]^q? (X=B, Al, Si, P, Ga, Ge, As, Zn), in the β‐ and γ‐[SiW₁₂O₄₀]^4? geometric isomers, in the derivative Dawson anion [P₂W₁₈O₆₂]^6?, and in the most symmetrical Lindqvist [W₆O₁₉]^2? anion and its derivative [W₁₀O₃₂]^4?. In this article, we show that the geometry employed in the calculation of NMR chemical shifts in polyoxotungstates is extremely important if we want to be quantitative. Using very large basis sets of QZ4P quality and taking into account the conductor‐like screening model (COSMO) to account for solvent effects (aqueous and organic solutions), good geometries were found for the polyoxoanions. From these optimal geometries the ¹⁸³W NMR chemical shifts were computed with the more standard basis sets of TZP quality and including spin–orbit corrections inside the zero‐order regular approximation (ZORA) to describe the relativistic effects of the internal electrons. With this strategy the mean absolute error between experimental and theoretical values was found to be less than 10 ppm, which is similar to the experimental error. We also discuss how the geometry of the polyoxoanion influences on the shielding.     

TiO2-Al2O3载体的制备及Ni2P/TiO2-Al2O3催化剂上的同时加氢脱硫和加氢脱氮反应

 以溶胶-凝胶法制备的 TiO2-Al2O3 复合氧化物为载体, 采用浸渍法制备了 Ni2P/TiO2-Al2O3 催化剂, 并用 X 射线衍射、N2 吸附脱附、红外和 X 射线光电子能谱等技术对催化剂进行了表征, 考察了载体中 TiO2 含量、焙烧温度及其制备方法对 Ni2P/TiO2-Al2O3 催化剂上同时进行噻吩加氢脱硫和吡啶加氢脱氮反应的影响. 结果表明, 以 Ni/P 摩尔比为 1/2 的前驱体制备的催化剂表面仅出现 Ni2P 物相; 当载体中 TiO2 的含量为 80%, 焙烧温度为 550 oC 时, Ni2P/TiO2-Al2O3 催化剂上加氢脱硫和加氢脱氮的活性最高. 在 360 oC, 3.0 MPa, 氢/油体积比 500, 液时体积空速 2.0 h?1 的条件下, 噻吩和吡啶转化率分别为 61.3%和 64.4%.     

碳化物修饰的有序介孔炭的制备及其催化肼分解性能

 以间苯二酚和甲醛为炭源, F127 (EO₁₀₆PO₇₀EO₁₀₆) 为结构导向剂, 在酸性水/乙醇溶液中引入 (NH₄)₆Mo₇O₂₄•4H₂O 或 (NH₄)₂WO₄ 溶液, 经静置自组装形成凝胶, 再于 N₂ 中焙烧即合成出金属碳化物修饰的有序介孔炭材料. 结果表明, 金属离子的种类和用量对碳化物的分散度和介孔炭的有序度影响很大. 通过控制金属离子的用量可制备出粒径为 3~5 nm 且高度分散在介孔炭骨架中的碳化物粒子. 与分步浸渍法相比, 一步法制备的碳化物具有更高的分散度和催化肼分解活性.     

基于溴钨灯和LED积分球光源的可调谐光谱分布及光谱匹配

采用溴钨灯和恒流驱动的LED混合作为积分球内部光源,提出了模拟退火算法作为光谱匹配算法,研究了光谱分布可调谐积分球光源的光谱匹配技术.仿真实验表明,该混合光源完全能够定量地模拟CIE-D65和等能光谱分布,且在辐射功率优于LED模拟结果的前提下,LED的数量分别减少79.8％和82.9％,平均相对误差分别减小10％和4...     

Porous WO3 from anodized sputtered tungsten thin films for NO2 detection

In this paper, porous WO₃ films were prepared by anodic oxidation of metallic tungsten (W) films deposited on alumina substrates. The structural and morphological properties of the porous WO₃ films were investigated using field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD). A large number of cracks appeared on the surface of films after anodization, which makes the films porous. The porous WO₃ sensors achieved their maximum response values to NO₂ at a low operating temperature of 150 °C. The porous WO₃ sensors showed high response values, great stability and fast response-recovery characteristics to different concentration of NO₂ gas due to the high specific surface area and special structural and morphological properties.     

Characterization of polyether‐poly(methyl methacrylate)‐lithium perchlorate blend electrolytes

Solid polymer electrolyte (SPE) systems based on interpenetrating blends of poly(ethylene oxide‐co‐propylene oxide) and poly(methyl methacrylate) host matrices, with lithium perchlorate as guest salt, were prepared. These electrolytes were presented as free‐standing films, and their thermal and electrochemical properties were characterized by conductivity and electrochemical stability measurements. The properties of the interpenetrating blends of poly(ethylene oxide‐co‐propylene oxide) and poly(methyl methacrylate) host matrices as the electrolyte component of a solid‐state electrochromic device are reported and the results obtained suggest that this electrolyte provides an encouraging performance in this application. The most conducting electrolyte composition of this SPE system is the formulation designated as SPE2‐0PC (5.01 × 10^?4 S cm^?1 at about 57°C). The lowest decomposition temperature was registered with the SPE6‐15PC composition (233°C). The average transmittance in the visible region of the spectrum was above 41% for all the samples analyzed. After coloration the device assembled with 71 wt% PC presented an average transmittance of 15.71% and an optical density at 550 nm of 0.61. Copyright © 2010 John Wiley & Sons, Ltd.     

Barium Sodium Niobate Powders and Thin Films: Preparation and Ferroelectric Behavior

Powders and thin films of barium sodium niobate, Ba₄Na₂Nb₁₀O₃₀, of filled tungsten bronze type ferroelectric were processed by a sol-gel route using barium metal, niobium ethoxide and sodium methoxide as precursors. Polycrystalline powder resulted after heat treating the gel powder at or above 650°C. Thin films of Ba₄Na₂Nb₁₀O₃₀ showed no preferred orientation on Si(100), Pt/Si(100) and sapphire substrates. Hysteresis measurements at 1 kHz for the thin films annealed at 750°C, obtained using a prehydrolyzed precursor solution, and gave remanent polarization of 17.34 µC/cm² and coercive field of 62.5 kV/cm. Microstructural investigation of surface morphology of these films revealed grains about 0.3 µm in size. Prehydrolysis of the precursor solution was found to be necessary to achieve dense films with ferroelectric properties.