Electrocatalytic oxidation of ethanol on Pt–Mo bimetallic electrodes in acid medium

Pt–Mo alloy electrocatalysts were prepared by an arc-melting furnace process to investigate the origin of their enhanced activity toward ethanol oxidation. Two Mo contents were chosen in zones of the binary phase diagram where they are supposed to form either a pure alloy mixture or a solid solution. Pt–Mo alloy catalysts were more active than Pt-alone. Gradual Mo dissolution at the electrode surface was observed after voltammetric and chronoamperometric measurements. The dissolved Mo contributed to the catalytic effect of the electrode as underpotentially deposited (upd) adatoms. This dissolution probably also leads to an increase in the electrode surface roughness. Low molybdenum content in the electrode material enhances the activity toward ethanol oxidation when compared to Pt-alone. Ethanol oxidation was also investigated by in situ infrared reflectance spectroscopy in order to determine the presence of adsorbed intermediates like CO species. Acetaldehyde, acetic acid and CO₂ were also found by spectroscopic experiments.     

镍铁型焊条焊接高强球铁接头云纹实验解析研究

镍铁型铸铁焊条已经相当广泛地用来焊接QT60—2球墨铸铁。然而,研究工作表明,这些焊接接头的强度较低。本文首次利用密栅云纹法研究了单向拉伸焊接接头的受力状况,获得了接头区域的全场位移、应变和应力分布。从焊接接头应变和应力分布的不均匀性,分析了裂纹产生及扩展的原因,用扫描电子显微镜观察了断口形貌,发现有大量的球状物分布在断口上,这可能是导致焊接接头低应力破断的原因。这一次现有助于改进镍铁型铸铁焊条的性能,提高接头的强度。     

单电源等离子-MIG焊方法

本文提出了一种使用一个陡降特性的焊接电源同时为两个电弧供电的单电源等离子-MIG 焊方法.试验研究了该方法的电流分配与调节特性、电压关系与电位关系、熔滴过渡与电弧形态等电弧特性.结果表明.该法是一种简单可行且有利于生产应用的新的等离子-MIG 焊方法.     

9%Ni钢焊接熔合区的氢致裂纹与马氏体带的关系

利用金相法、超高温显微镜及超高压透射电子显微镜技术,对9%Ni 钢焊接熔合区马氏体带的特性,拉应力对9%Ni 钢焊接熔合区组织,性能的影响进行了探讨。试验得出用Cr17Ni13Mn8W3奥氏体钢焊条焊接9%Ni 钢时,熔合区马氏体带中包含具有孪晶精细结构的马氏体,该马氏体带的相变滞后于热影响区的马氏体,其中的残余奥氏体稳定性不高,在拉应力作用或低温条件下易于转变成马氏体,从而增加了熔合区氢致裂纹倾向。提出了9%Ni 钢焊接熔合区氢致裂纹形成的模型。     

OBSERVATION ON SPUTTERING SURFACE OF ALLOYS IN GLOW DISCHARGE

Glow discharge cathodic sputtering of alloys containing second phase precipitates or injectedoxide particles has been observed with energy dispersive X-ray spectrometer and scanningelectron microprobe.It was shown that the formation of cones during the sputtering in thesealloys is due to masking of the matrix by glow sputtering second phase precipitates or oxideparticles.At steady state,the density of cottes were found to be a function of the densities pre-cipitates or oxide particles in bulk alloy.In addition to the changes of local sputtering rate,theelectrostatic effect may play a role on the formation fo cones.     

SELF-INTERACTION COEFFICIENTS OF Ca AND Mg IN DILUTE Sn-BASED SOLUTION

The interaction coefficients of Ca.Ti and Mg in the dilute Sn-based solution have been de-termined at 1500℃.Experimental measurements were taken by equilibrating the slag-alloysystems with metallic Sn as flux and graphite as reducing agent under Ar atmosphere mixedwith different portion of CO.It was found that a considerable error may produce if thecoefficients of ε_(Ca)~(Ca),ε_(Mg)~(Mg)and ε_(Ti)~(Ti)in the molten Sn were neglected when the activities of thecomponents CaO,MgO and TiO_2 in the slags were estimated by this method.     

Morphological effects of ceramide on DMPC/DHPC bicelles

Freeze fracture electron microscopy and dynamic light scattering were applied to characterize the morphological changes of DMPC/DHPC bicellar systems induced by the addition of ceramides. The results demonstrate a tendency of the DMPC/DHPC aggregates to evolve forming elongated or tubular structures with the increase of the temperature. At 20°C, low concentrations of ceramide promote the appearance of elongated structures with twisted zones. Higher concentrations of this lipid lead to the formation of liposomes along the elongated structures. The increase of the temperature to 40°C induces the growth of the structures containing low concentrations of ceramide forming branched aggregates. In samples with high amounts of ceramide, the increase of temperature causes phase separation and the formation of a mixed system composed by liposomes and multilamellar tubules. The morphological effects induced by ceramides in this new membrane model give new insights for the role played by this lipid in biological membranes.     

Tomography of insulating biological and geological materials using focused ion beam (FIB) sectioning and low-kV BSE imaging

Tomography in a focused ion beam (FIB) scanning electron microscope (SEM) is a powerful method for the characterization of three-dimensional micro- and nanostructures. Although this technique can be routinely applied to conducting materials, FIB–SEM tomography of many insulators, including biological, geological and ceramic samples, is often more difficult because of charging effects that disturb the serial sectioning using the ion beam or the imaging using the electron beam. Here, we show that automatic tomography of biological and geological samples can be achieved by serial sectioning with a focused ion beam and block-face imaging using low-kV backscattered electrons. In addition, a new ion milling geometry is used that reduces the effects of intensity gradients that are inherent in conventional geometry used for FIB–SEM tomography.     

Cryogenic EBSD on ice: preserving a stable surface in a low pressure SEM

Naturally deformed ice contains subgrains with characteristic geometries that have recently been identified in etched surfaces using high-resolution light microscopy (LM). The probable slip systems responsible for these subgrain boundary types can be determined using electron backscattered diffraction (EBSD), providing the etch features imaged with reflected LM can be retained during EBSD data acquisition in a scanning electron microscope (SEM). Retention of the etch features requires that the ice surface is stable. Depending on the pressure and temperature, sublimation of ice can occur. The equilibrium temperature for a low pressure SEM operating at 1 × 10(-6) hPa is about -112°C and operating at higher temperatures causes sublimation. Although charging of uncoated ice samples is reduced by sublimation, important information contained in the etch features are removed as the surface sublimes. We developed a method for collecting EBSD data on stable ice surfaces in a low pressure SEM. We found that operating at temperatures of <-112°C reduced sublimation so that the original etch surface features were retained. Charging, which occurred at low pressures (<1.5 × 10(-6) to 2.8 × 10(-5) hPa) was reduced by defocusing the beam. At very low pressures (<1.5 × 10(-6) hPa) the spatial resolution with a defocused beam at 10 kV was about 3 μm in the x-direction at -150°C and 0.5 μm at -120°C, because at higher temperature charging was less and only a small defocus was needed to compensate it. Angular resolution was better than 0.7° after orientation averaging. Excellent agreement was obtained between LM etch features and EBSD mapped microstructures. First results are shown, which indicate subgrain boundary types comprised of basal (tilt and twist) and nonbasal dislocations (tilt boundaries).