High current density 3D electrodes manufactured by technical embroidery

Embroidery techniques allow flexible construction of 3D electrodes, which can form the conductive backbone in ultra-thick electrodes. 3D structures were manufactured by combination of stainless steel yarn, Cu wire, polyester (PES) fabric and Cu/Ni-coated PES web. Alkaline solutions of 9,10-anthraquinone-1,5-disulfonate or 1,2-dihydroxy-9,10-anthraquinone-3-sulfonate (Alizarin Red S) were used as reversible redox systems to characterise the electrodes by voltammetry in a flow cell. The height of the diffusion-limited current for the reversible cathodic reduction of the 9,10-anthraquinoide group was used as measure for the electrode performance. Compared to plane Cu electrodes, an increase in the diffusion-limited cathodic current density by factor 3–5 was obtained.     

A Spectro-Microscopic Approach for Thin Film Analysis: Grain Boundaries in mc-Si and Sn/SnO2 Nano Particles

 Synchrotron radiation based spectro-microscopy is shown to be an exciting tool for elemental analysis in the field of heterogeneous interfaces, thin films, and device technology. Results are reported, taken with a spectrometer that enables the combination of a photoemission electron microscope (PEEM) with photoelectron spectroscopies (XPS, UPS) operated at a high brilliance undulator beam line at BESSY. The properties of mc-Si (multi crystalline silicon) are of interest because of their applications in low priced photovoltaic devices. An example of how to analyze the surface potentials of such surfaces without removing the native oxide is given. Tin nano-scale particles are shown to be the decisive factor affecting the corrosion prevention of passivated tinplate surfaces.     

A novel experimental method for potential controlled electrochemical impedance spectroscopy

Abstract  In many cases, impedance spectroscopy on electrochemical systems is performed in combination with a potentiostat. The common way of combining a potentiostat and a frequency response analyzer has a number of restrictions. Bandwidth limitations and artifacts from the setup distort the impedance data in sometimes unpredictable manners, and special care has to be taken in physical interpretation of such data. Therefore, potential controlled measurement of artifact-free impedance spectra in a wide range of frequencies is desirable. In this work, a novel experimental method is presented in which the more reliable two-probe impedance spectroscopy is combined with a potential control by a potentiostat without interfering each other. Results obtained on passive zinc by two-probe EIS, the classical potentiostat—EIS combination and the new setup are compared with each other. For an application of the proposed method in measurements of solid state systems, the specific problems are discussed. Graphical abstract        

Deterministic and stochastic effects near the convective onset

The pure conduction state of a horizontal layer of fluid heated from below becomes unstable with respect to a convecting state when the temperature difference exceeds a critical value. We examine the question of how real, physical systems evolve from conduction to convection. Most experimental cells contain geometric or thermal inhomogeneities which render the bifurcation to convection imperfect. In that case the pure conduction state never exists and the convecting state evolves continuously and smoothly as the temperature difference is raised. When a sufficiently perfect experimental cell is constructed to eliminate this route to convection, then dynamic imperfections will usually prevail. When the temperature difference across the cell is raised, the vertical gradients in the sidewalls evolve at a rate which differs from that in the fluid. The resultingtransient horizontal thermal gradients initiate the convective flow. This phenomenon can be eliminated by providing sidewalls which have the same thermal diffusivity as that of the fluid. When that is done, the convective flow is started by random noise which exists in any experimental system. Analysis of experiments shows that the noise source is considerably stronger than thermal noise, but its origin is unclear at this time.     

Non-oberbeck-boussinesq effects in gaseous Rayleigh-Bénard convection

Non-Oberbeck-Boussinesq (NOB) effects are measured experimentally and calculated theoretically for strongly turbulent Rayleigh-Bénard convection of ethane gas under pressure where the material properties strongly depend on the temperature. Relative to the Oberbeck-Boussinesq case we find a decrease of the central temperature as compared to the arithmetic mean of the top- and bottom-plate temperature and an increase of the Nusselt number. Both effects are of opposite sign and greater magnitude than those for NOB convection in liquids like water.     

Contributions to the Experimental Investigation of the Nascent Polymerisation of Ethylene on Supported Catalysts, 1

A detailed investigation of the kinetics, morphology and polymer properties observed during the polymerisation of ethylene on a Ziegler‐Natta catalyst at very short times (t ≥ 40 ms) in a novel, quenched‐flow reactor is presented. It was found that for times shorter than a tenth of a second, the observed rate of polymerisation was significantly higher than expected, and that the crystallinity of the nascent ethylene homopolymer was of the order of 25 to 30% – much lower than expected. Evidence is presented that shows that fragmentation is essentially complete in a small fraction of a second.

     

大尺寸单级高频脉冲管制冷机研究

本文简要介绍近年来在德国吉森大学开展的大尺寸单级高频脉冲管制冷机研究的主要进展.该大尺寸脉冲管已能达到较低的制冷温度并在60～80 K获得较高的效率,在国际上处出领先水平.文中首先介绍了理论模拟结果,然后介绍实验存在的问题及其改进,特别是提出了一个改进回热器温度不均匀分配的方案,得到了很好的验证.     

Particle Growth During the Polymerisation of Olefins on Supported Catalysts, 1 – Nascent Polymer Structures

It is shown that the relationship between the catalyst/polymer structure, process conditions and final product properties needs to be addressed in more detail. From an industrial point of view, the interest starts from the need to control the growth of the catalyst/polymer particle during the polymerisation process. This first part of a two‐part review discusses the different factors that can influence the physical properties of the nascent polymer, and how these can impact the evolution of particle morphology.