Electrochemical behaviour of heat-treated AlZnMg alloys in chloride solutions containing sulphate

The electrochemical corrosion and passivation of Al5Zn1.7Mg0.23Cu0.053Nb alloys, submitted to different heat treatments (cold-rolled, annealed, quenched and aged, and quenched in two steps and aged), in sulphate-containing chloride solutions, has been studied by means of cyclic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS). The cyclic polarization curves showed that sulphate addition to the chloride solution produced a poor reproducible shift of the breakdown potential to more positive potentials. The repassivation potentials, much more reproducible, and practically separating the passive from the pitting potential region, were slightly displaced in the negative direction with that addition. When the alloys were potentiodynamically polarized in the passive potential region, sulphate was incorporated in the oxide film, thus precluding chloride ingress. In addition, Zn depletion was favoured, whereas Mg losses were avoided. Different equivalent circuits corresponding to different alloys and potentials in the passive and pitting regions were employed to account for the electrochemical processes taking place in each condition. This work shows that sulphate makes these alloys more sensitive to corrosion, increasing the fracture properties of the surface layer and favouring the pitting attack over greater areas than chloride alone.     

Studies on the synthesis and properties of poly(amide-azomethine)

Homopolymer and copolymer of poly(amide-azomethine) were synthesized from the corresponding diamines and dialdehydes. The polymerization was proceeded in the mixed solvent of o-chlorophenol and m-cresol (1: I by volume) at 0 °C for I S h. The inherent viscosities of the new aromatic poly(amide-azomethine)s are in the range of 0.51 to 2.31 dl/g. These polymers were soluble in sulfuric and formic acid. The TGA results show that no weight loss up to 400 °C under nitrogen atmosphere, which suggests the relatively good thermal stabilities.     

Air sampling of volatile sex pheromone components in a closed jar

A cotton wool plug, used as the source for pheromone release, was placed in closed 1-quart Mason jars, either at the mouth or at the rear of the jar. Air sampling of the two components of the sex pheromone (total 2.2 mg at the source) of the almond moth (Ephestia cautella) female showed that the saturation period near the source in still air was 20–22 hr and that far from the source was 40–50 hr, reaching a level of less than 1 ng/ml air. The ratio between the components (Z,E)-9,12-tetradecadienyl acetate, designated D, and (Z)-9-tetradecenyl acetate designated M, in the air was close to the original ratio for both sampling sites, albeit somewhat richer in the more volatile (Z)-9-tetradecenyl acetate (source 77.023.0 DM, air 73.0– 74.327.0–25.7; source 80.119.9, air 77.622.4; source 25.174.9, air 23.976. 1 DM). The total amount of pheromone per milliliter of air was two to three times larger near the source than far from it at the early stages of the evaporation and saturation process. When the amount of pheromone applied to the source was tripled (7 mg), the amount far from the source was almost tripled, or the saturation time was cut by factor of two to three.     

注重形式美与提高鉴赏力——中国绘画鉴赏的理论与实践

长期以来,美术鉴赏教育走进了忽视形式美、专注所谓意义与价值的误区。培养"欣赏形式美的眼睛"是美术鉴赏教育的重点与难点。本文对"形式"、"形式美"、"艺术的形式本体"、"绘画艺术本体"概念进行了梳理和界定;紧密结合中国绘画鉴赏的教育实践,提出了提高中国绘画鉴赏力的审美理念、路径、方法。     

复杂电磁暂态下变压器差动保护异常动作行为分析及对策

随着电力系统结构与组成的复杂性增加,变压器差动保护发生原因不明的误、拒动作几率明显上升,给电网安全带来隐患,也影响工业生产的正常运行.分析变压器经历外部故障切除、有载合闸、非线性负荷投入、换流变合闸等复杂电磁暂态过程时基于二次谐波制动的差动保护误动的机理,指出TA局部暂态饱和、非线性特性元件的相互作用是造成上述保护误动的根本原因.并对换流变压器差动保护在故障情况下长延时动作的原因进行分析,基于相电压突变量和差流突变量的时差,提出一种能有效解决上述问题的变压器差动保护判据。在任何非故障的异常情况下,该时差总是存在,而内部故障时该时差很小,可以将变压器故障和其经历的异常运行状态相区分.通过大量的试验对该判据的可行性和有效性进行验证.     

Influences of 2.5wt% Mn addition on the microstructure and mechanical properties of Cu-Al-Ni shape memory alloys

The influences of 2.5wt%Mn addition on the microstructure and mechanical properties of the Cu-11.9wt%Al-3.8wt%Ni shape memory alloy(SMA) were studied by means of scanning electron microscopy(SEM),transmission electron microscopy(TEM),and differential scanning calorimeter(DSC).The experimental results show that Mn addition influences considerably the austenite-martensite transformation temperatures and the kind of martensite in the Cu-Al-Ni alloy.The martensitic transformation changes from a mixedβ_1→β'_1...     

Deformation behavior and microstructure of an Al-Zn-Mg-Cu-Zr alloy during hot deformation

The hot deformation behavior and microstructures of Al-7055 commercial alloy were investigated by axisymmetric hot compression at temperatures ranging from 300°C to 450°C and strain rates from 10-2 to 10 s-1,respectively.Microstructures of deformed 7055 alloy were investigated by transmission electron microscopy (TEM).The dependence of peak stress on deformation temperature and strain rate can be expressed by the hyperbolic-sine type equation.The hot deformation activation energy of the alloy is 146 kJ/mol....     

Microscopic characterization of semi-solid aluminium alloys

The microstructural evolution and element distribution of the Al-4Cu-Mg alloy during semi-solid compression were investigated,and the precipitate behavior and dislocation morphology were discussed.The experimental results show that the microstructure,the number of CuAl2(θ phase) precipitates,and the dislocation density of the Al-4Cu-Mg alloy depend apparently on the process parameters.More segregation of Cu at the grain boundary happens with an increase of deformation temperature and a decrease of strain ra...     

Electrical conductivity changes of bulk tin and Sn-3.0Ag-0.5Cu in bulk and in joints during isothermal aging

The changes of electrical conductivity(resistance) between Sn-3.0Ag-0.5Cu solder joints and printed circuit board(PCB) assembly during aging at 125℃were investigated by the four-point probe technique.The microstructural characterizations of interfacial layers between the solder matrix and the substrate were examined by optical microscopy and scanning electronic microscopy.Different types of specimens were designed to consider several factors.The experimental results indicate that electrical conductivitie...     

A force control high-order single-step-β method (HSM) for substructure pseudo-dynamic testing

This paper proposes a new technique which introduces the high-order single-step-β method(HSM)into the experimental study on the substructure pseudo-dynamic testing(SPDT).The technique is based on the proposed concept of equivalent shear stiffness which can meet the requirement of the HSM algorithm.A study is done to theoretically validate the technique by the numerical analysis of two-storey shear building structure,in comparison of the proposed substructure pseudo-dynamic testing algorithm with the central difference method(CDM).Then,a full-scale SPDT model,the three-storey frame-supported reinforced concrete short-limb masonry shear wall structure,is designed and tested to simulate the seismic response of the corresponding six-storey structure and verify the proposed force control HSM technique.Meanwhile,the techniques of both stiffness correction and force control are suggested to control algorithmic error,control error and measurement error.The results indicate that the force control HSM can be used in the full-scale multi-degree-of-freedom(MDOF)substructure pseudo-dynamic testing before descent segment of structure restoring force properties.