化学溶液沉积法制备WO3•2H2O薄膜及其电致变色性能

目的研究具有不同微观结构的WO_3·2H_2O薄膜的电致变色性能。方法采用化学溶液沉积法在FTO玻璃上制备WO_3·2H_2O薄膜,通过加入不同的形貌控制剂(柠檬酸或草酸铵),制备不同纳米结构的WO_3·2H_2O薄膜。采用X射线衍射仪(XRD)和扫描电子显微镜(SEM)分析薄膜的成分结构和微观形貌,利用紫外可见光分光光度计对薄膜在波长为200～1000nm范围内的透光性进行研究,并通过电化学工作站对薄膜进行电化学性能分析。结果采用柠檬酸作为形貌控制剂制备的WO_3·2H_2O薄膜的透光性高达82%左右,其在着色和褪色状态的透过率差值为36.2%。通过添加柠檬酸或草酸铵作为形貌控制剂制备的WO_3·2H_2O薄膜均呈现出纳米片状结构,纳米片的厚度分别为5～15 nm和50～60 nm,但是采用柠檬酸制备的WO_3·2H_2O具有较多的间隙和裂缝,使其表现出了较好的电致变色性能。结论具有间隙和裂缝的纳米WO_3·2H_2O薄膜增加了薄膜与电解质的接触面积,减少了离子扩散的路径距离,更小的纳米结构可以提供更多的化学活性位点,从而表现出较好的电致变色性能。     

Synthesis and characterization of ceria quantum dots using effective surfactants

The stable and crystalline phase of different surfactants (CTAB, PEG and SDS) capped CeO₂ nanoparticles were directly synthesized by chemical precipitation method at room temperature. The effects of surfactants on the structural and optical properties of nanoparticles are characterized. The optical properties of the nanoparticles were investigated by UV–visible and PL spectroscopy. The effects of surfactants with observed band shifts are due to quantum confinement effect. The optical band gap values are determined by simple energy wave equation and Tauc plot method. The observed particle sizes are very closer to the Bohr exitonic radius. The emission bands such as violet, blue, green and orange are observed in PL spectra. The PL integrated intensity ratio of the UV emission to the deep-level green emission (I_UV/I_DLE) for CTAB, PEG and SDS capped CeO₂ nanoparticles are observed. The XRD measurement shows that CeO₂ has cubic fluorite structure having the particle size 6–10 nm. The lattice strains were detected by Williamson–Hall plot method. The surface morphology of the nanoparticles is studied by SEM and FESEM analysis. TEM images show that the particles are nearly spherical in shape with diameter of 5–10 nm. Using FTIR spectra, the functional groups of the ceria are identified.     

Molecular dynamics simulation of mechanical properties of Ni–Al nanowires

We employed molecular dynamics simulations to study mechanical properties of Ni–Al nanowires by calculating the stress–strain response of the wires under various loading conditions. For this purpose, nanowires were subjected to uniaxial strain at different strain rates and temperatures using embedded atom model potential. The behaviour of the wires at lower and higher strain rates was investigated, and the yield and rupture strain values and also Young’s Modulus were obtained which are essential factors for the ductility of the wires. This work indicates that how the stress–strain response of the nanowires are affected by varying strain rates and temperatures.     

W6Mo5Cr4V2/A100复合材料的制备及摩擦性能

为了提高A100钢的摩擦学性能,采用气雾化法制备纯A100钢粉末及分别添加10%、17%、23% W6Mo5Cr4V2高速钢的W6Mo5Cr4V2/A100合金粉末,再利用粉末冶金工艺制备W6Mo5Cr4V2/A100复合材料。研究不同含量W6Mo5Cr4V2钢对复合材料力学性能和摩擦性能的影响,并探讨其磨损机理。结果表明,随着W6Mo5Cr4V2钢含量的增加,复合材料的硬度先上升后下降,且摩擦因数和磨损率都有不同程度的降低,但是材料的密度和韧性都略微下降。当W6Mo5Cr4V2钢含量为17%时,复合材料的摩擦性能最优,这与其优异的微观结构和力学性能有着密不可分的关系。     

Effects of water-gas shift reaction on simulated performance of a molten carbonate fuel cell

A molten carbonate fuel cell (MCFC) is simulated. In order to determine the effects of the water-gas shift reaction, the calculated results such as temperature distribution, voltage distribution, conversion and performance, are compared with those calculated excluding the shift reaction. Uniformity in the temperature profile is deteriorated due to the shift reaction. At the entrance, hydrogen is consumed rapidly in order to reach the equilibrium state of the shift reaction. The conversion of hydrogen decreases along the direction of gas flow because of hydrogen generated by the shift reaction. Therefore, when the shift reaction is excluded, the conversion of hydrogen is higher than that in a practical cell. Additionally, at the same current density, the voltage calculated without the shift reaction would be higher than the real value. The effect of the shift reaction on the voltage distribution and cell performances is quite small.     

Study on the role of niobium in corrosion mechanism of low-alloy pipeline steel in H2S-saturated solution

In this study, the role of Nb addition on the corrosion behavior of low-alloy steel exposed to H₂S solution is studied by means of microstructure, macro/microsurface morphology characteristics, type of corrosion product, cross-sectional structure and elemental distribution. The addition of Nb is a route to refine grains and improve corrosion resistance. The surface formation process of iron sulfides changes from homogeneity to dispersion at the initial corrosion stage when Nb is added to steel. However, the transformation process and crystal structure of iron sulfides are not affected by the addition of Nb. The elemental distribution of corrosion products is not affected by Nb addition although thick and compact corrosion products are formed on the specimen surface of Nb steel. A schematic model is proposed to clarify the difference of the corrosion mechanism in atomic and molecular level.     

固溶处理对Cr23Ni7Mo2Cu0.6双相不锈钢组织与性能的影响

利用XSL-4-12箱式热处理炉、ZEISS金相显微镜、HRS-150数显洛氏硬度计及拉伸试验机研究了固溶处理对Cr23Ni7Mo2Cu0.6双相不锈钢组织与性能的影响。结果表明,铁素体含量随着固溶温度的升高而增加,在930~960 ℃之间铁素体与奥氏体面积比达到1∶1,σ相的含量随着固溶温度的升高而逐渐减少,在960 ℃时仅有少量σ相存在于相界处,1020 ℃时由于锻造造成的奥氏体相分布不均的情况也得到了改善。合金硬度与抗拉强度随着固溶温度的上升呈现先下降后上升的趋势,分别在1020 ℃和1050 ℃达到最小值94.4 HRB和547 MPa,伸长率则随着固溶温度的升高呈现先上升后下降的趋势,在990 ℃时达到峰值41.5%。综合钢丝拉拔变形过程中材料的硬度、塑韧性及组织均匀性对材料成形性能的影响,Cr23Ni7Mo2Cu0.6双相不锈钢的固溶温度宜选择1020 ℃。     

A two-dimensional optical cross-connect with integrated waveguides and surface micromachined crossbar switches

The design, fabrication and test results of an all-optical cross-connect, which uses electrostatically actuated micromechanical digital mirrors to steer optical signals in a network of planar waveguides, are presented. The substrate consists of a network of spliced planar waveguides on silica substrates. The switches, located at the waveguide intersections, are formed with an electroplated T-structure consisting of a horizontal perforated square plate suspended by four elastic beams. When operated, the horizontal plate is pulled up making the mirror move out of the optical path thus steering the beam. An 8×8 switch array has been fabricated and tested. Actuation and relaxation switching times near 3 ms have been demonstrated with an actuation voltage of 120 V. The optical insertion loss for the array typically varied from 2.3 dB for a single trench in the optical path (shortest optical path) to 8 dB for 15 trenches in the optical path (longest optical path).     

Evaluation of the impact of the physical dimensions and material of the semiconductor chip on the reliability of Sn3.5Ag solder interconnect in power electronic module: A finite element analysis perspective

This paper primarily focuses on an evaluation study for the temperature cycling capability of tin silver solder interconnect in power electronic applications by the impact of die dimensions and die material properties. The study was investigated on finite element analysis perspective on chip/solder/substrate structure. A commercially available chip was chosen in the finite element analysis (FEA) as the nominal base die. Two thermal cycle profiles were utilised. The effect of die area, die thickness and material properties (Si and SiC) on the thermal cycling capability of the solder layer was investigated from FEA perspective. From the FEA, it was concluded that decrease in die thickness resulting in increment of thermal cycling capability of solder layer for both material (Si and SiC). Increase in die area increases the thermal cycling capability of solder. For higher ΔT thermal cycle, solder under SiC die perform better than solder under Si die in terms of thermal cycling capability. When the die thickness become smaller than a threshold value of the thermal cycle regime, solder under Si die have better thermal cycling capability than solder under SiC die. Additionally a parametric study was undertaken for a SiC chip/substrate structure under high ∆ T temperature cycling profile for solder layer geometric parameter (wetting angle, titling angle and thickness). From the parametric study which utilised design of experiments (DoE), a wavelet radial basis surrogate model was generated. A sensitivity analysis was performed on surrogate model in order to identify the most influencing parameter. From the sensitivity analysis, it was concluded that wetting angle and solder layer thickness of solder layer have significant impact on the thermal cycling capability of the solder layer.     

Durability evaluation of hexagonal WO3 electrode for lithium ion secondary batteries

We evaluated the durability of a hexagonal tungsten oxide (h-WO₃) electrode for use as the negative electrode in lithium ion secondary batteries (LIBs). H-WO₃ has attracted attention as an electrode for LIBs owing to its large hexagonal tunnels, in which Li ions can be inserted. However, when a charge-discharge cycling test was carried out in the voltage range 2.5–1.0 V (vs LiCoO₂) for 500 cycles, its discharge capacity decreased by 73% compared with the initial value. To clarify the reasons for the degradation, various types of analysis were performed. The deposited layer on the electrode and changes in both the crystalline structure and the electrolyte composition are considered to be the main reasons for the degradation. The observed changes in the valence of W also affected the degradation. We also report that the voltage range plays an important role in increasing the durability.