泡沫铝连接件焊接工艺的应用现状与展望

泡沫铝兼具结构与功能特性,为充分发挥泡沫铝的各种性能,常将其与致密金属进行复合得到三明治结构,以提高其综合力学性能并降低成本。三明治结构的连接方法众多,而焊接手段是最可靠的连接方式。首先介绍了泡沫铝的性能特点及焊接难点,综述了其焊接方法,包括常规电弧焊、激光焊、钎焊、扩散焊、搅拌摩擦焊、等离子焊以及超声波焊,再对各工艺的局限性进行阐述,最后对泡沫铝连接件焊接工艺的发展方向进行浅析。     

Challenges of Diffusion Bonding of Different Classes of Stainless Steels

Solid state diffusion bonding is used to produce monolithic parts exhibiting mechanical properties comparable to those of the bulk material. This requires diffusion of atoms across mating surfaces at high temperatures, accompanied by grain growth. In case of steel, polymorphy helps to limit the grain size, since the microstructure is transformed twice. The diffusion coefficient differs extremely for ferritic and austenitic phases. Alloying elements may shift or suppress phase transformation until the melting range. In this paper, diffusion bonding experiments are reported for austenitic, ferritic, and martensitic stainless steels possessing varying alloying elements and contents. Passivation layers of different compositions are formed, thus affecting the local diffusion coefficient and impeding diffusion across faying surfaces. As a consequence, different bonding temperatures are needed to obtain good bonding results, making it difficult to control the deformation of parts, since strong nonlinearities exist between temperature, bonding time, and bearing pressure. For martensitic stainless steel, it is shown that it is very easy to obtain good bonding results at low deformation, whereas ferritic and austenitic stainless steels require much more extreme bonding parameters.

     

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.     

全组分木质活性炭球的制备及其乙烯吸附性能研究

目的 制备全组分木质活性炭球,应用于乙烯吸附,筛选出乙烯吸附效果最好的活性炭球制备工艺。方法 以木材液化物为原料,探究不同的固化时间对制备的全组分木质活性炭球微观形貌的影响,利用场发射扫描电子显微镜观察其微观结构,通过氮气吸附-解析等温线计算样品孔径分布及其比表面积;使用气相色谱仪,结合乙烯吸附标准曲线,分析时间及吸附剂用量对4种活性炭球吸附乙烯性能的影响。结果 随着固化时间的增加,碳球表面趋于光滑、内部结构越来越致密,石墨化程度逐渐提高,比表面积和孔容逐渐减小。当固化时间为0.5 h时,比表面积高达2 073 m²/g,乙烯吸附量高达197.99 mg/g,约3 h达到吸附平衡。结论 全组分木质活性炭球能有效吸附乙烯气体,固化时间太长,活性炭球内部孔隙减少,不利于吸附乙烯气体。活性炭球孔容越大,乙烯吸附效果越好。     

Improved Tribocorrosion Properties of Ti6Al4V Alloy by Anodic Plasma Electrolytic Oxidation

Ti6Al4V alloy has good corrosion resistance due to the formation of the passive oxide films on the surface of Ti6Al4V alloy. However, Ti6Al4V alloy has poor tribocorrosion resistance in the seawater environment. Herein the present work, plasma electrolytic oxidation (PEO) with the electrolyte of glycerol and sodium borate is used to generate PEO coatings on the surface of Ti6Al4V alloy to improve its tribocorrosion properties. The microstructure and tribocorrosion properties of PEO coatings are investigated by using scanning electron microscopy, X-ray diffraction, and tribometer, respectively. The growth kinetics and the tribocorrosion mechanisms of PEO coatings are discussed in detail. It is shown in the results that PEO coatings deposited on the surface of Ti6Al4V alloy are composed of rutile and anatase phases. The surface hardness and thickness of PEO coatings are enhanced with the increase of the voltage and time. The wear rate of Ti6Al4V alloy with PEO coatings is significantly reduced in artificial seawater.     

A Perspective on Emerging and Future Sintering Technologies of Ceramic Materials

Novel sintering methods have emerged in the recent past years, which have raised great interest in the scientific community. Relying on electric field effects, high heating rates, the use of mechanical pressure, or hydrothermal conditions, they offer fundamental advantages compared to conventional sintering routes like minimizing the energy consumption and enhancing the process efficiency. This perspective aims at explaining these effects in a general way and presenting the status quo of using them for the processing of high-performing ceramic materials. In detail, this work focuses on flash sintering, ultrafast high-temperature sintering, spark plasma sintering, cold sintering, and photonic sintering methods based on different light sources. The specificities, potentials, and limitations of each method are compared, especially in the light of a possible industrialization.     

Vic-dioximes: A new class of sensitive materials for chemical gas sensing

Vic-dioximes, a class of organic chemical compounds, are proposed and characterized for the first time as sensitive materials for volatile organic compound sensing with sorption based chemical gas sensors. Their peculiar sensing properties described in this work originate in the oxime functional group which is a powerful H bond donor interacting strongly but reversibly with H bond acceptors. These specific interactions result in a high preferential enrichment of analyte molecules with H bonding acceptor capabilities in the sensitive material. Accordingly, sensitivity and selectivity for these compounds of vic-dioxime based sensors are high. The advantageous sensing properties are demonstrated in this work with quartz crystal microbalance sensors using 11 selected volatile organic compounds and a set of vic-dioximes varied in their substituents. Vic-dioximes with short alkylthiol substituents were found highly sensitive to such H bond acceptors as organic amines, alcohols, and esters with partition coefficients up to 26,000. At the same time they showed low affinity for aromatic compounds and chlorocarbons. Vic-dioximes are considered powerful sensing materials and interesting for practical use in chemical gas sensor arrays.     

Factors responsible for the aggregation behavior of hydrophobic polyelectrolyte PEA in aqueous solution studied by molecular dynamics simulations

Self-association (i.e. interchain aggregation) behavior of atactic poly(ethacrylic acid) PEA in dilute aqueous solution as function of degree-of-neutralization by Na⁺ counter-ions (i.e. charge fraction f) was investigated by molecular dynamics simulations. Aggregation is found to occur in the range 0 ≤ f ≤0.7 in agreement with experimental results compared at specified polymer concentration C_p = 0.36 mol/l in dilute solution. The macromolecular solution was characterized and analysed for radius-of-gyration, torsion angle distribution, inter and intra-molecular hydrogen bonds, radial distribution functions of intermolecular and inter-atomic pairs, inter-chain contacts and solvation enthalpy. The PEA chains form aggregate through attractive inter-chain interaction via hydrogen bonding, in the range f < 0.7, in agreement with experimental observation. The numbers of inter-chain contacts decreases with f. A critical structural transition occurs at f = 0.7, observed via simulations for the first time, in R_g as well as inter-chain H-bonds. The inter-chain distance increases with f due to repulsive interactions between COO− groups on the chains. PEA-PEA electrostatic interactions dominant solvation enthalpy. The PEA solvation enthalpy becomes increasingly favorable with increase in f. The transition enthalpy change, in going from uncharged (acid) state to fully charged state (f = 1) is unfavorable towards aggregate formation.     

基于NaOH刻蚀玻碳电极的电化学传感器在检测膀胱癌DNA中的应用

制备了一种基于活化的玻碳电极的新型电化学DNA生物传感器,可用于膀胱癌DNA的检测.通过循环伏安法(CV)实现玻碳电极在NaOH溶液中的刻蚀,使电极表面负载大量官能团,为DNA提供连接位点,由Laviron方程计算得到玻碳电极表面的羧基浓度为 1.022×10-6 mol/cm2.亚甲基蓝(MB)作为电化学检测的杂交指示剂.采用原子力显微镜(AFM)对刻蚀后的电极进行了形貌表征.在最优杂交条件下,通过差分脉冲法(DPV)计算出最佳检测限为5.677×10-13 mol/L(n=5),适用目标 DNA浓度范围1×10-8 mol/L~1×10-12 mol/L.该传感器有望用于实际样品中膀胱癌DNA的快速检测.