不同合成过程对溶胶-凝胶法制备的ZnO/Ag纳米复合材料光催化性能的影响

以乙酸锌、硝酸银为前驱体,二乙醇胺作为稳定剂,利用溶胶-凝胶法分别采用一步法和两步法制备得到ZnO以及ZnO/Ag纳米复合粉体。所有ZnO/Ag复合物中Ag的含量均为3%(摩尔分数)。对所制备样品的结构和光学性质通过XRD、SEM、TEM、XPS、PL、UV-vis进行了表征,进而以甲基橙为模拟污染物进行了光催化测试。结果表明,不同方法制备得到的ZnO/Ag纳米粉体晶粒均匀,无明显团聚现象,面心立方结构的金属Ag吸附在纤锌矿结构的ZnO表面形成异质结。与纯ZnO相比,掺Ag极大地改善了样品在紫外光下的光催化活性。对不同合成工艺的比较表明,用溶胶-凝胶一步法制备的ZnO/Ag复合物的光催化活性最高,经紫外光照射70min可完全降解甲基橙。     

Effect of friction stir processing and hybrid reinforcements on copper

In this research, a copper based surface composite was fabricated through dispersing hybrid composite particles onto its surface through friction stir processing (FSP) technique. Optical micrographs and scanning electron microscopy images indicates finer refinement of grains and particles dispersion into matrix along with its bonding and particle separation. As per the outcomes of microhardness analysis, hardness of the developed surface composite shows increment with increase in dispersion of volume fraction of hybrid particles. Strength of the developed copper surface composite exhibited a positive trend with introduction of hybrid reinforcement particle onto the surface of the composite but yet again ductility reduced. Wear resistance of the composite increased with reinforcement addition and the same was supported through worn out surface morphology. Fluctuations in friction coefficient value reduced with increase in particles, as for the presence in BN particles while the average frictional coefficient value was observed increasing. A reduction in corrosion rate was observed with increase in reinforcement particle dispersion onto copper matrix through FSP.     

On the effect of tool offset in hybrid-FSW of copper-aluminium alloy

Tool offset is one the most significant parameters in joining of dissimilar materials by friction stir welding (FSW) process. An investigation is carried out on the effect of tool offset toward thermal history, material flow pattern, mechanical properties, welding force, and weld joint morphology. It was found that offsetting toward aluminum side along with a plasma-assisted heat source is an efficient approach to address one of the most important apprehensions in aluminum-copper solid-state welding process. The offset influences the amount of intermetallic at the joint interface and in-effect impacts on final strength and material flow behavior. The optimum and continuous layer of intermetallic produces the maximum weld joint strength. The specimen welded with optimum tool offset shows the highest strength using 55 A plasma current in hybrid friction stir welding process.     

Investigation of magnetic field-assisted EDM of composites

The Electrical Discharge Machining (EDM) technique was performed under the magnetic field influence to determine the material removal mechanism as well as surface roughness (SR) of nonmagnetic material. This study presents an exploration of the hybrid EDM technique assisted by magnetic field, with an aim to improve process performance. Herein, magnetic field intensity, peak current, duration of pulse-on/off, tool electrode material, and SiC percentage distribution were opted as the machining parameters. The chosen parameters were analyzed for their effects on the material removal rate (MRR) and SR while machining of SiC-reinforced aluminum-based metal matrix composites. Taguchi methodology was adopted for optimization of process parameters to achieve better MRR and lower SR. The experimental results witnessed improved surface finish and enhanced material removal ability of the process and also inferred that the magnetic field-assisted EDM facilitated the process stability.     

Laser–arc hybrid welding of high-strength steel and aluminum alloy joints with brass filler

The laser–tungsten inert gas hybrid welding method was adopted to realize the welding process between Q460 high-strength steel and 6061 aluminum alloy. The influence of the dual heat source on the mechanical properties and microstructure of the welded joints are discussed. In addition, the effects of including a copper–zinc interlayer on the microstructure, elemental distribution, and mechanical properties of welded joints are also studied. The results show that the mechanical properties of the welded joints are influenced by the relative heat inputs of the two heat sources and the Cu-Zn interlayer. The braze welded joint fabricated without a Cu-Zn interlayer fractured at an Al-Fe intermetallic compound (IMC) layer formed at the interface, whereas the braze welded joint fabricated with a Cu-Zn interlayer fractured at an Al-Cu IMC layer formed at the interface. Comparisons show that the maximum tensile shear load of the brazed welded joint with the Cu-Zn interlayer was increased by about 20% relative to that formed without the interlayer. The formation of Al-Fe IMC layer in the deep penetration joint was inhibited by the combined effect of the dual heating sources and the Cu-Zn interlayer.     

Light‐Activated,Multi‐Semiconductor Hybrid Microswimmers

Using a dynamic fabrication process, hybrid, photoactivated microswimmers made from two different semiconductors, titanium dioxide (TiO₂) and cuprous oxide (Cu₂O) are developed, where each material occupies a distinct portion of the multiconstituent particles. Structured light‐activated microswimmers made from only TiO₂ or Cu₂O are observed to be driven in hydrogen peroxide and water most vigorously under UV or blue light, respectively, whereas hybrid structures made from both of these materials exhibit wavelength‐dependent modes of motion due to the disparate responses of each photocatalyst. It is also found that the hybrid particles are activated in water alone, a behavior which is not observed in those made from a single semiconductor, and thus, the system may open up a new class of fuel‐free photoactive colloids that take advantage of semiconductor heterojunctions. The TiO₂/Cu₂O hybrid microswimmer presented here is but an example of a broader method for inducing different modes of motion in a single light‐activated particle, which is not limited to the specific geometries and materials presented in this study.     

Surface integrity of Inconel 718 by hybrid selective laser melting and milling

ABSTRACT

While selective laser melting (SLM) offers design freedom of metal parts with much less material consumption, there exist several limitations, including high surface roughness, low-dimensional accuracy, and high tensile residual stresses. To make functional parts with high form accuracy and superior surface integrity, an as-SLM part needs finishing to remove the deposited surface material. The integration of machining and SLM creates a hybrid manufacturing route to overcome the inherited limitations of SLM. However, little study has been done to characterise surface integrity of an as-SLM part followed by machining (e.g. hybrid SLM-milling). In this paper, surface, integrity including surface roughness, microstructure, and microhardness, have been characterised for IN718 samples processed by the hybrid process. It has been found that microhardness varies with the scan direction and the use of coolant in the subsequent milling, and surface integrity can be significantly improved by the hybrid SLM-milling route.     

基于马尔可夫的锂电池组充电均衡控制研究

针对动力锂离子电池组充电后期过程中因单体电池性能差异而造成的可用容量不均衡、使用寿命缩短等问题,改进了一种结构较为简单、能量转移灵活的无损能量转移型均衡电路;提出了基于马尔可夫决策算法的动力锂电池组充电均衡控制方案,对单体电池间能量转移方向进行预测,决策出最优转移路径;通过实验结果分析,均衡效率、均衡效果均明显提高,实现了动力锂离子电池组充电后期过程中的充电均衡,证明了该均衡电路及均衡控制方案的可行性。     

引入扰动补偿的多电机滑模协同控制研究

目的 解决多电机协同控制时容易受到非线性和外界扰动等不定因素的影响。方法 基于多电机偏差耦合控制结构,与引入扰动补偿的混合非奇异终端滑模变结构控制相结合,并与传统PI(Proportional Integral)调节器控制效果做仿真对比。结果 本文所提控制算法通过计算机仿真软件进行验证分析,该算法能够使得电机在启动时效果较好,转速误差在受到扰动时效果优于传统PI控制约8.50%;电机转矩在受到扰动后控制效果更加理想,几乎不存在迟滞时间就能达到新的负载转矩值;在受到负载扰动时转速误差波动较小,优于传统PI控制约8.83%。结论 通过计算机仿真验证得出,引入扰动补偿后的混合非奇异终端滑模变结构控制系统的响应时间和收敛速度、控制性能和鲁棒性都要优于传统PI控制的。