Reduction of Fine Ores in Argon‐Hydrogen Plasma

The steel industry is a major source of global CO₂ emission. Larger reductions of greenhouse gases are the challenge to develop new processes, like Hydrogen Plasma Smelting Reduction (HPSR). The present paper shows physical and chemical fundamentals for the reduction of iron oxides with hydrogen plasma. The behaviour of different hematite iron ores during melting and reduction with hydrogen plasma were investigated with thermogravimetry and a laboratory plasma furnace. The path of iron oxides during smelting and reduction in the Fe‐O phase diagram are described. Reduction tests in the laboratory furnace show the possibility to reduce hematite iron ores with hydrogen plasma in a short time with high utilization degrees without direct CO₂ emissions.     

Fast multipole method based solution of electrostatic and magnetostatic field problems

Abstact Applications of boundary element methods (BEM) to the solution of static field problems in electrical engineering are considered in this paper. The choice of a suitable BEM formulation for electrostatics, steady current flow fields or magnetostatics is discussed from user's point of view. The dense BEM matrix is compressed with an enhanced fast multipole method (FMM) which combines well-known BEM techniques with the FMM approach. An adaptive grouping scheme for problem oriented meshes is presented along with a discussion on the influence of the mesh to the efficiency of the FMM. The computational costs of the FMM algorithm are analyzed for typical problems in practice. Finally, some electrostatic and magnetostatic numerical examples demonstrate the simple usability and the efficiency of the FMM. Communicated by: U. Langer     

Ottokraftstoffe aus erneuerbarem Methanol

For synthesis of emission-reduced gasoline fuels from regenerative methanol, catalyst and process optimization was carried out as part of the joint research project Kopernikus „Power-to-X”. For this purpose, a laboratory test plant had to be designed and commissioned, and process parameters for an optimized fuel quality had to be worked out considering variations of catalyst and feed. The precisely adjustable isothermal synthesis conditions allow the specific adjustment of the chemical properties of the high-octane petrol produced.     

Influence of Power-to-Fuel Plant Flexibility Towards Power and Plant Utilization and Intermediate Hydrogen Buffer Size

Conversion of intermittent renewable energy into synthetic fuels and chemicals is required to secure long-distance transport and feedstock for chemical industry. Due to the fluctuating energy generation, process intensification and feed flexibility are essential. This contribution investigates the importance of feed flexibility on the buffer size with applying a 20:80 scenario of wind/solar energy generation. The degree of power and plant utilization are calculated. With the capability to accept a lower load bound of 17 % after only 10 min, a minimum tank capacity of only 1.3 h is calculated to avoid a fuel plant stop throughout a calendar year. Additional tank capacity for peak power compensation in the range of ∼10 h is beneficial for the utilization degree of power and under the prerequisite of a load-flexible fuel plant.     

Epitaxial n- and p-type Emitters for High Efficiency Solar Cell Concepts

Reducing the module prices by increasing the efficiency of solar cells is one of the major challenges in today＇s photovoltaic research. The emitter formation by epitaxial growth offers a cost-efficient and faster alternative to the standard furnace diffusion process. The efficiency potential of epitaxial emitters 〉 22% has already been proven using a single wafer, low pressure, chemical vapour deposition tool. The purpose of this work is to show the potential of epitaxially grown emitters by APCVD （atmospheric pressure chemical vapour deposition） compared to diffused emitters. The APCVD formation of epitaxial emitters at 1,050 ~C can be realised as high throughput inline process and only takes 1-2 min, whereas the diffusion process using POCI3 takes up to 60 min. Simulations show an increase in voltage of AVoc = ＋10 mV and a reduction in saturation current ,1o of 30% for the epitaxial emitter. The lifetime experiments of solar cells with epitaxial emitter exhibit a diffusion length Leff〉 750μm and an emitter saturation current of Joe 〈 50 fA/cm2 on a planar 10 Ω2cm p-type FZ wafer. Another important aim of this work is to evaluate the limitations of epitaxial emitters due to high thermal budget, interface recombination and the change of reflective properties on textured wafers due to the deposition process. Solar cell efficiencies up to 18.4% on p-type and 20.0% on n-type wafers presented in this paper underline that the emitter epitaxy by APCVD is a competitive process for the emitter formation.     

Micro-spectroscopy on silicon wafers and solar cells

Micro-Raman (μRS) and micro-photoluminescence spectroscopy (μPLS) are demonstrated as valuable characterization techniques for fundamental research on silicon as well as for technological issues in the photovoltaic production. We measure the quantitative carrier recombination lifetime and the doping density with submicron resolution by μPLS and μRS. μPLS utilizes the carrier diffusion from a point excitation source and μRS the hole density-dependent Fano resonances of the first order Raman peak. This is demonstrated on micro defects in multicrystalline silicon. In comparison with the stress measurement by μRS, these measurements reveal the influence of stress on the recombination activity of metal precipitates. This can be attributed to the strong stress dependence of the carrier mobility (piezoresistance) of silicon. With the aim of evaluating technological process steps, Fano resonances in μRS measurements are analyzed for the determination of the doping density and the carrier lifetime in selective emitters, laser fired doping structures, and back surface fields, while μPLS can show the micron-sized damage induced by the respective processes.     

Vergleich des Koaleszenzverhaltens ruhender und umströmter Wasser‐in‐Öl‐in‐Wasser‐Einzeltropfen

Phase inversion of a water‐in‐oil emulsion to a water‐in‐oil‐in‐water double emulsion is practically used for liquid/liquid separation. For successful separation in the water leg the coalescence of the internal droplets with the surrounding continuous water phase is decisive. The determination of this coalescence phenomenon is applied for the process design. Therefore, single water‐in‐oil‐in‐water drops are investigated under static and dynamic conditions by means of high speed imaging. The influence of physical and geometrical parameters on the coalescence time and partial coalescence is determined.     

Schrifttumsberichte

Ohne Zusammenfassung     

Synchronous,asynchronous, and causally ordered communication

Summary.  This article studies characteristic properties of synchronous and asynchronous message communications in distributed systems. Based on the causality relation between events in computations with asynchronous communications, we characterize computations which are realizable with synchronous communications, which respect causal order, or where messages between two processes are always received in the order sent. It is shown that the corresponding computation classes form a strict hierarchy. Furthermore, an axiomatic definition of distributed computations with synchronous communications is given, and it is shown that several informal characterizations of such computations are equivalent when they are formalized appropriately. As an application, we use our results to show that the distributed termination detection algorithm by Dijkstra et al. is correct under a weaker synchrony assumption than originally stated. Received: November 1992/Accepted: July 1995