Anwendung dilatometrischer Messungen bei der Entwicklung von Glasloten und reaktiven Metallloten zum Fügen von Hochtemperaturbrennstoffzellen

The principle of operation of solid oxide fuel cells (SOFCs) is very simple. However, the fact that very different materials are used for the individual components requires advanced thermal joining techniques to join them in a functional manner. Two very distinct designs have established themselves for the two different intended applications: decentralised power generation (stationary SOFCs) on the one hand, and power converters for vehicles (mobile SOFCs) on the other hand. As a consequence, alternative techniques for joining the individual components are also required. The principal joining process for the stationary SOFC design consists of joining individual steel plates with a glass sealant in an electrically insulating way so that they form an SOFC stack. For the mobile fuel cell design, the SOFC stack consists of individual thin steel cassettes. The window frame of the cassettes, which is made of ferritic chromium steel, is brazed to the ceramic layer of the zirconium oxide solid electrolyte using a filler metal. The material used is a silver‐based brazing filler metal which contains only small amounts of copper oxide (CuO) and titanium hydride (TiH₂) as wetting agents. Both joining processes must be applicable in normal atmospheric air, i. e. under oxidative conditions. R&D activities continue for improving the efficiency and long‐term operational stability of the technology to such an extent that SOFCs will become ready for the energy sector market. The two joining techniques described cannot yet be considered standard processes. They, too, will require continuous improvement with respect to reproducibility, endurance and strength of the joints. The Special Joining Techniques working group at Forschungszentrum Jülich uses specially modified dilatometric techniques as suitable quick replacement methods for studying and measuring the joining characteristics of the materials without having to manufacture complex and expensive SOFC stacks. The shrinkage processes in the glass sealant joints are simulated and measured in the μm range using a special dilatometer. In this way, the amount of glass sealant – which is decisive for tightness and bonding – and the process parameters can be determined in advance. With a vertical dilatometer, the melting behaviour of the reactive silver filler metals is examined with respect to melting point shift, viscosity and void ratio, and as a function of the metal additives (Al) and the process atmosphere.     

Electron Beam Technologies for Preparation of Polymeric Materials Used for Waste Water Treatment, Agriculture, and Medicine

Radiation research results in the field of polymeric materials, obtained in the last few years by electron beam irradiation of aqueous solutions containing appropriate monomer mixtures, such as acrylamide, acrylic acid and vinyl acetate, are presented. Two types of polymeric flocculants for waste water treatment and three kinds of hydrogels for agriculture and medicine are described. The effects of radiation absorbed dose, radiation absorbed dose rate, and chemical composition of the irradiated solutions upon the polymeric materials characteristics are discussed. The required absorbed dose levels to produce the polymeric flocculants are in the range of 0.3 to 9 kGy and 4 kGy to 12 kGy for hydrogels. Some experimental results obtained by testing polymeric flocculants with waste water from food industry are given. Polymeric material processing was developed on a pilot plant level with ALID-7 electron linear accelerator of 5.5 MeV and 0.7 kW, built in the Electron Accelerator Laboratory of the Institute of Atomic Physics, Bucharest. A new facility permitting the application of simultaneous electron beam and microwave irradiation is presently under investigation. Preliminary results demonstrated that some polymeric flocculant characteristics, such as linearity, were improved by simultaneous electron beam and microwave treatment. Also, the absorbed dose levels decreased and intrinsic viscosity increased, respectively, by about two times by this new material processing method.     

Combined Electron Beam and Microwave Treatment for Flue Gas Purification

The results of a research program concerning the application of the electron beam EB) irradiation, microwave MW) irradiation and simultaneous electron beam and microwave EB + MW) irradiation for removing nitrogen oxides NOX) and sulfur dioxide SO₂) in simulated Due gases are presented. Several microwave applicators and reaction chambers used for NO_X and SO₂ removal tests are also presented. The additional use of MW energy and EB energy or the use of MW energy only proved to be a promising method for removal of pollutants in view of the reduction of power consumption and flue gas treatment process cost. Experiments performed at lower temperature 65-70°C) of the gaseous mixture air, Argon up to 7%, H₂O up to 25%, CO₂ up to 10%, SO₂ up to 2000 ppm, NO_X up to 1000 ppm, NH₃ added in stoichiometric amounts) demonstrated a higher SO₂ removal efficiency with lower absorbed dose. Promising results are obtained especially for SO₂ removal efficiency: up to 80% for MW, 85% for EB irradiation and up to 90% for EB + MW irradiation. A considerable amount of SO₂ can be separated even without MW, EB or EB + MW irradiation due the spontaneous reaction with ammonia at gaseous mixture temperature below 70°C. The most important conclusion concerning MW irradiation is that efficiency of removal of pollutants strongly depends on microwave applicator structure type, residence time and MW power level.     

电子束固化树脂基复合材料中碳纤维表面改性研究

利用阳极氧化方法和偶联剂对碳纤维表面的物理和化学性质进行改性，采用原子力显微镜（AFM）和X射线光电子能谱（XPS）分析了碳纤维表面改性前后的形貌和化学成分的变化，利用Keaelble法计算了碳纤维的表面能。研究结果表明，阳极氧化改性的碳纤维表面粗糙度增加，表面活性；表面活性官能闭增多，表面能中极性成分增加明显，碳纤维表面引入的活性氮和化学吸附的碱性物质使电子束固化复合材料界面处的引发剂中毒，复合材料界面性能减弱，与电子束固化工艺相匹配的偶联剂在碳纤维与树脂基体之间形成化学桥，使电子束固化复合材料界面性能得到明显提高。     

Fluor‐Kohlenstoff‐Nanoschichten zur gezielten Oberflächenfunktionalisierung. Fluorine‐Carbon Nano Coatings for Specific Surface Functionalization

This article concerns some aspects of the research and development work, which is done within a project of the German Federal Ministry of Education and Research (BMBF) entitled: “nano functionalization of interfaces for data‐, textile‐, building‐, medicine‐, bio‐, and aerospace‐ technology”. In the following the broad field of applications of a surface modification on a nanometer scale is discussed. Also some scientific methods to characterize surface modifications of this kind are discussed. By means of low pressure plasma technology it is possible to functionalize surfaces and thus to well adjust their properties with respect to their application. This is done without changing the bulk material characteristics. The surfaces of the treated workpieces are covered by an ultrathin, i.e. only a few nanometer thick, fluorine‐carbon polymer layer by a plasma process. The physical and chemical surface properties, such as surface energy, roughness (on nanometer scale), dynamic wetting behaviour, or the adhesion properties against other materials, can be simple changed by varying the plasma process parameters. It is shown, that in future this surface modification will meet a broad field of applications.     

Plasmachemische Gasphasenabscheidung – eine Technologie zur Deposition organischer und anorganischer Schichten. Plasma Enhanced Chemical Vapor Deposition – a Thin Film Technique for Organic and Inorganic Layers

Plasma enhanced chemical vapor deposition (PECVD) has a wide range of interest for thin films up to some μm thickness. It has widespread applications for high quality dielectric and semiconducting silicon alloys at deposition temperatures below 450 °C and pressures at 1 mbar on plane substrates and attracts growing attention for the surface modification of polymers. The PECVD takes advantages of the possibility to alter the film properties in a wide range easily, and the coatings can achieve a variety of useful properties unobtainable by other coating techniques. An environmentally friendly plasma chemical reactor etch cleaning of SiO_x, SiN_x and other film materials can be applied by changing the process gas and without breaking the vacuum. PECVD can be used in a fixed substrate and continuous substrate flow mode. An capacitively coupled parallel‐plate electrode assembly using radio‐frequency (RF) excitation of the discharge is most widely used for substrate areas up to a few square meters. Among the capacitively excitation an inductively and electromagnetically excitation at frequencies in the RF and UHF range has also succeeded in achieving a high rate PECVD. Two applications are presented to show the characteristics and the potential of this technique, the PECVD of semiconducting hydrogenated amorphous silicon, intrinsic or doped, with low power densities using monosilane as a source gas for solar cells, thin films transistors and digital image sensors and the plasma polymerisation of organosilicon protection layers employing the HMDSO monomer and high power densities for mirrors and lenses.     

The Itinerant 2D Electron Gas of the Indium Oxide (111) Surface: Implications for Carbon‐ and Energy‐Conversion Applications

Transparent conducting oxides (TCO) have integral and emerging roles in photovoltaic, thermoelectric energy conversion, and more recently, photocatalytic systems. The functional properties of TCOs, and thus their role in these applications, are often mediated by the bulk electronic band structure but are also strongly influenced by the electronic structure of the native surface 2D electron gas (2DEG), particularly under operating conditions. This study investigates the 2DEG, and its response to changes in chemistry, at the (111) surface of the model TCO In₂O₃, through angle resolved and core level X‐ray photoemission spectroscopy. It is found that the itinerant charge carriers of the 2DEG reside in two quantum well subbands penetrating up to 65 Å below the surface. The charge carrier concentration of this 2DEG, and thus the high surface n‐type conductivity, emerges from donor‐type oxygen vacancies of surface character and proves to be remarkably robust against surface absorbents and contamination. The optical transparency, however, may rely on the presence of ubiquitous surface adsorbed oxygen groups and hydrogen defect states that passivate localized oxygen vacancy states in the bandgap of In₂O₃.     

Tuning Surface Wettability and Adhesivity of a Nitrogen‐Doped Graphene Foam after Water Vapor Treatment for Efficient Oil Removal

An environment‐friendly water vapor treatment for realizing a highly hydrophobic (contact angle ≈147.5°) and oleophilic N‐doped graphene foam (NGF) for efficiently removing oil from oil/water emulsions is presented. 3D porous networks of NGF with high N content are prepared by subjecting a mixture of graphene oxide and 5 vol% pyrrole to a hydrothermal process; the mixture is then freeze‐dried and annealed under a N₂ atmosphere. The surface wettability and adhesivity are tuned through water vapor treatment by forming a low‐surface‐energy hydrocarbon layer, with no chemical modification. The effectiveness of the hydrophobic/oleophilic NGF in removing oil from an oil/water emulsion is demonstrated.     

Nanobiotechnologie: Innovationen für Medizin und Technik. Nanobiotechnology: Innovations for medicine and technics

Bio‐ and nanotechnology are two important fields of research, which give reason to new technological prospects for our future. The especial high potential of innovation at the interface between these disciplines is only entered specifically for a few years. This article gives a review of results and activities in the field of nanobiotechnology and points out related prospects of application.     

Fe2VO4 Hierarchical Porous Microparticles Prepared via a Facile Surface Solvation Treatment for High‐Performance Lithium and Sodium Storage

Preventing the aggregation of nanosized electrode materials is a key point to fully utilize the advantage of the high capacity. In this work, a facile and low‐cost surface solvation treatment is developed to synthesize Fe₂VO₄ hierarchical porous microparticles, which efficiently prevents the aggregation of the Fe₂VO₄ primary nanoparticles. The reaction between alcohol molecules and surface hydroxy groups is confirmed by density functional theory calculations and Fourier transform infrared spectroscopy. The electrochemical mechanism of Fe₂VO₄ as lithium‐ion battery anode is characterized by in situ X‐ray diffraction for the first time. This electrode material is capable of delivering a high reversible discharge capacity of 799 mA h g^?1 at 0.5 A g^?1 with a high initial coulombic efficiency of 79%, and the capacity retention is 78% after 500 cycles. Moreover, a remarkable reversible discharge capacity of 679 mA h g^?1 is achieved at 5 A g^?1. Furthermore, when tested as sodium‐ion battery anode, a high reversible capacity of 382 mA h g^?1 can be delivered at the current density of 1 A g^?1, which still retains at 229 mA h g^?1 after 1000 cycles. The superior electrochemical performance makes it a potential anode material for high‐rate and long‐life lithium/sodium‐ion batteries.     

CVD‐Diamantschleifstifte für den Werkzeug‐ und Formenbau. Abrasive Pencils for Tool and Die Making Coated by Diamond CVD

Recently developed compeDIA®‐ abrasive pencils have been produced and tested for the machining of cemented carbide molding tools. In order to produce abrasive pencils, carbide base plates have been grinded and coated with a diamond layer by a Hot‐Filament‐CVD‐process. The testing of the abrasive pencils took place with an ultra‐precision grinding machine on carbide workpieces. Surface roughness of the workpiece and its wheel life were the criteria for evaluation. For the specific adjustment of the grain size of the abrasive pencils, the adequate coating parameters were worked out, and the dependencies on basic influencing variables at coating procedures, such as nominal diameter and grinding length, were calculated. In order to be able to coat the grinded base plates with enough film adhesion, a practical pre‐treatment method was developed and tested, which removes the fringe zone, that was damaged during the grinding process. At present, the costs for the coating process are uneconomically high, though. By means of large‐scale production in connection with an automated pre‐treatment and coating it would be possible to lower the costs so far that they are on the same cost level with other coatings like TiN or TiAlN. The CVD‐Diamond abrasive pencils are very appropriate for tool and die making. It is to be expected that through further development of tools and through process optimization, the quality of the wrought workpiece can be ameliorated and surface finishes of R_a < 0,3 μm can be reached. The wheel life could be increased to appropriate values by optimization of the coating technology. The range of the machining parameters, in which the grinding process can be accomplished expediently without leading to a broken die, have been worked out. Afterwards, a die‐casting component with typically shaped elements was designed and an adequate molding tool prototype was crafted. With that, the basic conditions for tool‐ and die‐making were worked out in order to put into practice a fast and flexible machining of cemented carbide molding tools with the aid of those innovative abrasive pencils. In contrast to the traditional molding tool material made of brass, clear advantages in tool life can be made in the production of miniature serial‐parts by drawing, deep‐drawing or extrusion.