Response time and mechanism of Pd modified TiO2 gas sensor

In this work, gas response properties of Pd modified TiO₂ sensing films are discussed when exposed to H₂ and O₂. TiO₂ films are surface modified in PdCl₂-containing solution by the dipping method and treated for different treatment times to get different surface states. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Kröger–Vink defect theory are used to characterize the sensing films. The gas response properties indicate that the sensor response time which related to the rate of change of sensor resistance is affected by the activation energy (E). In particular, the sensor treated at 900 °C for 2 h exhibits a response time of about 20–240 ms when exposed to H₂ and 40–130 ms when exposed to O₂ at 500–800 °C.     

矿井主要通风机变频系统改造

针对我国煤炭行业风机系统的应用现状,开发了基于高压变频器的风机自动控制系统.系统采用“二拖二,互为备用”方案,利用高压变频器对风机进行调速控制,实现了系统根据实际所需的风量来调节电机转速,提高了可靠性,获得了较好的控制性能和良好的节能效果.     

基于转镜运动补偿的弹丸同步摄影技术研究

弹丸的空间飞行姿态是武器性能的一项重要指标。为了使数字摄影相机实现对高速运动弹丸运行轨迹的成像,设计了一种基于转镜运动补偿的弹丸同步摄影装置。在高速数字相机前设置一面反射转镜,当弹丸进入跟踪视场时,利用转镜的旋转补偿弹丸的空间运动,使得由转镜反射到相机像面的弹丸图像偏移在许可范围内,实现同步摄影过程。实验证明该方法能够满足常规弹丸同步摄影的需求。     

纳米金属粉在火炸药中应用进展

高活性、高热值纳米金属粉的应用是提高火炸药产品性能的重要途径.综述了纳米金属粉对推进剂、凝聚相炸药、云爆炸药、铝热剂的性能提高作用,总结了纳米金属粉的几种改性方法,如纳米金属/聚合物复合、纳米金属/炭复合、小分子助剂表面包覆、高分子聚合物表面接枝、气相沉积、颗粒微观整形等,指出了纳米金属粉应用研究的重点方向:纳米硼粉、...     

利用支持向量机补偿温度对光纤光栅传感的影响

不同于以往温度、应变与光纤Bragg光栅(FBG)峰值波长偏移量之间的数学模型,本文提出利用支持向量机(SVM,support vector machine)补偿温度的影响,并以FBG压力传感器为例,利用标定的压力传感器数据对SVM模型的惩罚系数C和径向基核函数(RBF)核参数γ进行优化,得到SVM温度补偿模型,选择核参数γ为100、惩罚系数C为16。经过补偿后,压力传感器的零位温度系数和灵敏度温度系数由补偿前的34.5%/℃和34.2%/℃减小到1.7×10-5%/℃和7.7×10-5/%/℃。充分说明,利用SVM补偿温度对FBG压力传感器的影响是有效的。     

用数字散斑法测量铜/铝复层板拉伸变形

提出了一种基于数字散斑相关法和双目立体视觉技术的全场三维变形测量方法,实现了对爆炸焊接制备的铜/铝复层材料的变形测量。研究了该方法所涉及的数字散斑相关算法、三维坐标、位移和应变计算等关键技术,借助于VC++6.0开发环境,研制并开发了用于铜/铝复层板全场变形测量的试验系统及其软件。为了验证本文所述测量方法的可行性,进行了精度验证实验和铜/铝复层板单向拉伸试验,且对复层板拉伸试验结果与有限元软件Abaqus数值模拟结果进行了对比分析。结果表明:本文方法的应变测量精度优于0.5%,与引伸计测得的结果基本相当;测得的应变极值分布与有限元模拟结果很吻合;在板料发生颈缩前,塑性应力-应变模拟曲线与试验结果很吻合;整个变形过程中位移-载荷模拟曲线的变化趋势与试验结果一致,模拟得到的极限载荷的相对误差为0.06%～2.25%。实验结果说明,数字散斑方法是一种精确获得复层板料全场应变的有效手段。     

基于SOM网的风电变流器故障诊断

我国新疆、甘肃、宁夏、内蒙、浙江、黑龙江、江苏、广东等都在大规模建设风电场,这些风电场建成后,其故障维护就有了很大市场.以新疆风电场为基础,尝试开发用于风力机故障智能诊断的系统.首先介绍了风力机及其变频器系统的结构,分析了变频器的故障机理.使用SOM神经网络对风机变流器进行了诊断,用数据验证了诊断结果.把传统的电力电子设备故障诊断技术与新疆风力机变频器的故障诊断相结合,为风电大面积推广应用产生了积极作用.     

Pd-doped TiO2@polypyrrole core-shell composites as hydrogen-sensing materials

A core-shell composite consisting of polypyrrole (PPy) nanofibers and TiO₂ was synthesized by using PPy nanofibers as the core and TiO₂ as the shell. The TiO₂@PPy composite substrate was doped with Pd nanoparticles via chemical reduction. The resulting Pd–TiO₂@PPy nanocomposite was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Brunauer–Emmett–Teller (BET) adsorption analysis before it was utilized to fabricate a hydrogen sensor. Compared with sensors based on TiO₂@PPy or PPy, the Pd–TiO₂@PPy sensor was highly sensitive and selective to hydrogen gas, exhibiting a fast response time in air at room temperature. The Pd–TiO₂@PPy-based sensor exhibited a sensitivity of 8.1% toward 1 vol% of H₂ gas, which is much larger than the sensitivities of sensors based on only TiO₂@PPy and PPy nanofibers. The excellent reproducibility, stability and selectivity of the Pd–TiO₂@PPy nanocomposite make it a high potential candidate for hydrogen sensors.     

Enhanced H2S sensing performance of TiO2-decorated α-Fe2O3 nanorod sensors

Pristine and TiO₂ nanoparticle-decorated Fe₂O₃ nanorods were synthesized via thermal oxidation of Fe thin foils, followed by the solvothermal treatment with titanium tetra isopropoxide (TTIP) and NaOH for TiO₂ nanoparticle-decoration. Subsequently, gas sensors were fabricated by connecting the nanorods with metal conductors. The structure and morphology of the pristine and TiO₂ nanoparticle-decorated Fe₂O₃ nanorods were examined via X-ray diffraction and scanning electron microscopy, respectively. The gas sensing properties of the pristine and TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensors with regard to H₂S gas were examined. The TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensor showed a stronger response to H₂S than the pristine Fe₂O₃ nanorod sensor. The responses of the pristine and TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensors were 2.6 and 7.4, respectively, when tested with 200 ppm of H₂S at 300 °C. The TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensor also showed a faster response and recovery than the sensor made from pristine Fe₂O₃ nanorods. Both sensors showed selectivity for H₂S over NO₂, SO₂, NH₃, and CO. The enhanced sensing performance of the TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensor compared to that of the pristine Fe₂O₃ nanorod sensor might be due to enhanced modulation of the conduction channel width, the decorated nanorods’ increased surface-to-volume ratios and the creation of preferential adsorption sites via TiO₂ nanoparticle decoration. The dominant sensing mechanism in the TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensor is discussed in detail.