Holz und Holzwerkstoffe in der Technik von heute und morgen

Wood and Woodmaterials in the Technology of Today and Tomorrow. Though wood on the market is under the pressure of numerous competing materials, its production and consumption increases on the whole world. Available are round logs, sawn lumber, sheetlike wood based materials such as plywood, particleboard, fiber building board and since some time glued structural parts. Continuous wood consumption is necessary for securing the beneficial effects of forests. In the Federal Republic of Germany and in most industrialized countries the production of particleboard increased in a parabolic manner. A special stimulation of wood consumption came by glued laminated structural parts. Firms working on this field founded the organization Glulam with the aim to standardize the production methods, the permissible stresses, the classification and dimensions of the sawn wood, the calculation of glued wood constructions and its behaviour in fire. On the basis of test results the minimum dimensions for fire resistance grades F 30 and F 60 (30 min. and 60 min.) are given. Large spans e. g. for halls, serving for various purposes, gymnasiums, covered tennis courts, ice rink halls, swimming baths, churches, warehouses, factory buildings, storage sheds, filling stations, shell roofs and bridges can be built with no other materials besides laminated timber with so little dead weight.     

Ressourcen‐ und Kosteneffizienz von Niederdruckplasmaprozessen

Ressource‐ and cost efficiency of low pressure plasma processes Two aspects have to be taken into consideration if new processes for surface treatment are to be introduced. The first one regards the costs for each part to be treated. To get a general idea some suppliers of plasma reactors and job coater were asked for the basis used for calculation of treatment or coating of polymer parts. The second aspect is related to resource efficiency, meaning how much material and energy is needed to treat the different components. This aspect will attract much more attention in the future. Both aspects also are crucial for dissemination of plasma technology and are in the focus of this paper.     

Abpumpverhalten von Roots‐ und Schraubenvakuumpumpen

Pump down characteristic of Roots pump combinations Combinations of roots pumps and screw type vacuum pumps are often used in industrial vacuum applications because of their high pumping capacity, their compact dimensions and their good energy efficiency. In load lock applications, the type of load control has a high influence on the evacuation time as well as on the energy efficiency of the pump combination. The operation limits of roots pumps are discussed and means to prevent an overload of the pump are introduced.     

Herstellung von Polymer‐ und Polymer‐Metalloxid‐Kompositschichten

Preparation of polymer and polymermetal oxide composite thin films Organic materials are not yet commonly used for optical interference layer systems. The reasons therefor are their low mechanical resistivity, their often more complex deposition techniques and their poorer optical properties compared with oxide thin films. However some organic materials offer special properties that are useful for the application in optical layer systems. Because of its high mechanical flexibility mechanical stress in layer systems can be reduced. Some organic materials show specific optical properties like fluorescence or intensive colors that can be used for optical layer systems. Hydrophilic and hydrophobic organic top coatings can improve the pollution behavior of optical layer systems. Therefore we present in this work some gas phase deposition techniques for organic substances and report about some basic optical and mechanical properties of thin films coated with these as well as some important process characteristics.     

Entwicklung und Eigenschaften von Magnesium‐Lithium‐Legierungen

Development and Properties of Magnesium‐Lithium‐Alloys The application of Lithium in Magnesium alloys extends the properties of these regarding smaller density and clearly increased ductility. Hereby can be met to demands even on the part of the automobile industry for damage‐tolerant, better ductile magnesium components. Investigations of hexagonal Magnesium Lithium alloys show promising results, which contain not only more balanced mechanical properties but also an improved corrosion behavior.     

Laserstrahl‐ und Reibschweißen von Magnesiumlegierungen

Laser Beam and Friction Welding of Magnesium Alloys The need for weight and cost reduction forces the engineer to develop new alloys with good options for design as well as to constantly optimize the industrial processes with regards to their utilizability and efficiency. With regards to these aspects it is of great interest to investigate the weldability of these newly developed alloys. The focus is put on both a high performance process and a special prosess for low heat influence. Furthermore, new methods will be presented which will make it possible to reduce the number of test runs as well as to identify influences and interactions between main process parameters and marks of quality.     

Zyklisches Werkstoffverhalten von Magnesium‐Druckguss‐ und ‐Knetlegierungen

Cyclic material behaviour of magnesium die castings and extrusions The cyclic deformation behaviour of the die castings AZ91 and AE42 and the extrusions AZ31 and AZ80 is investigated in strain controlled tension compression tests. The main topic of this investigation is the verification of the Masing and Memory behaviour. These two material properties are necessary for the component design by the local strain concept. The two die castings show approximately Masing behaviour, but the hysteresis of magnesium is different from the hysteresis of steel. For extrusions a totally different behaviour in tension and in compression direction can be observed. The hysteresis in experiment differs from the calculated hysteresis from the cyclic stress strain curve. The Masing behaviour is not observed because of the strong anisotropic behaviour in tension and in compression direction. All investigated magnesium alloys show the material memory M2.     

Auslegung und Fertigung von UHV‐Kammern

Design and manufacturing of UHV chambers The selection of materials, the finish of the surfaces, the design of the construction: What influence do these factors have in the area of ultra‐high vacuum? Which pumping power is actually required for the respective application? Why can it be difficult to achieve a suitable end pressure? The author gives an overview of the key points to be considered when designing and manufacturing chambers for the UHV. The article is not just about manufacturing, it also touches product safety and risk assessment issues.     

Beschichtungen und Evakuierung von Vakuum‐Solarkollektoren

Coating and Evacuation of Solar Collector Tubes The company NARVA, a traditional German producer of fluorescent lamps, has started in 2005 the development of a new vacuum absorber tube for collecting of solar energy for warmth of buildings or for process heat. By adapting the experience of lamp making NARVA is using their self produced soda lime glass, coated with Siliciumdioxide nano particles for the collector tubes. This coating gives better transmission, less corrosion and a behaviour like safety glass in case of destruction. A other interesting item in the development of the vacuum process is the „light oven”︁. By use the light oven it was possible to reach the necessary temperature on the absorber fin for an effective desorption of the water molecules from the surface of the fins and to reach the target vacuum.     

Herstellung und komplexe Charakterisierung von Metall‐Keramik‐Verbundschichten

Formation and characterization of metal‐ceramic coatings The influence of the formation process and used materials of metal‐ceramic coatings on the structural properties of the deposited layers were investigated and optimized to increase the mechanical properties. There the deposition of the metal‐ceramic‐layers occurred by a combination of electrophoretic and galvanic deposition with siloxane as bonding compound. Layers with a high ceramic content were successfully created. As ceramic components commercial silicon carbide and silicon nitride were used. Nickel and Copper respectively were applied as metal component to fill the porous ceramic structure with the aim to increase the strength of the layers, where nevertheless a pre nickel‐plating or pre cupper plating of the steel substrate X6Cr17 before ceramic component deposition had to be done to increase the adhesion of the layers. The layer characterization was made by optical microscopy and scanning and transmission electron microscopy, where especially the bonding of the single particles by the siloxane was in evidence.     

Eigenspannungsentwicklung und mechanisches Verhalten von c‐BN‐Schichten

To better understand the influence of layer defects on the adhesion strength of cubic boron nitride both computer simulations at a mesoscopic level and experimental analysis of fracture mechanical processes were carried out. This led to new important insights in obtaining higher adhesion strength and was usefully incorporated in processing of the layers.     

Untersuchung von Schmelz‐ und Rekristallisationsprozessen sowie Riss‐, Oxid‐ und Porenbildung beim Schweißen

Investigation of melting and re‐crystallization processes and of crack, oxide and pore formation during welding In the paper some known investigation methods of the primary re‐crystallization and of the structure of the crystallization front are discussed. All these methods have disadvantages, in some cases they cause a limited validity or are expensive. The presented new method is based on the micrographic recording of the melting and solidifying metal surfaces. The method overcomes the above‐mentioned disadvantages. It is able to investigate in the welding seams not only the primary re‐crystallization processes but also the secondary ones including the formation of cracks and pores and the appearance of non‐metallic inclusions like oxides. The facilities of the method are demonstrated on some examples of use.     

Reinigung von Vakuumbauteilen für UHV‐ und UCV‐Anwendungen

Cleaning of vacuum components for UHV and UCV applications Ultra‐clean vacuum components and assemblies are fundamental to some cutting edge high‐tech sectors like semiconductor industry, particle accelerators, and surface analytics. Exceptionally critical for these applications are particles that stick at the vacuum facing surfaces as well as desorption of water and hydrocarbons from the surfaces into the system, because this may interfere with the sensitive ultra‐high vacuum (UHV) and ultra‐clean vacuum (UCV) processes. In this contribution, some established cleaning methods and surface treatments are discussed with respect to their effect on reducing particle contamination and outgassing of water and organic compounds from stainless steel surfaces. It is clarified that the resulting cleanliness severely depends on the detailed steps during the surface treatment and subsequent cleaning. As a consequence, the discussed methods should be chosen and adapted with great care according to the specific demands of the final application area.     

Einfluss von Gussfehlern auf die Dauerfestigkeit von Aluminium‐ und Magnesiumgusslegierungen

Influence of casting defects on the endurance limit of aluminium and magnesium cast alloys The influence of porosity (voids and shrinkage) on the fatigue properties at very high numbers of cycles is shown for the alloys AZ91 hp, AM60 hp, AE42 hp, AS21 hp and AlSi9Cu3 produced by high pressure die casting. Fatigue tests performed with ultrasonic equipment up to 10⁹ cycles show that these alloys exhibit a fatigue limit. The mean endurance limits (50% failure probability) of the magnesium alloys are 8–50 MPa and of the aluminium alloy 75 MPa. Fatigue cracks initiate at porosity, and whether a specimen fractures or not depends on the stress amplitude and the area and the site of the defect. Regarding the cast defect as an initial crack, a critical stress intensity value (K_cr) may be found to propagate a crack until final failure. K_cr of the magnesium alloys is 0,80–1,05 MPa√m, and 1,80 MPa√m was found for AlSi9Cu3. Using K_cr it is possible to correlate the probability of different defect sizes and the failure probability at different stress amplitudes. Additionally, predictions of the influence of rare large casting defects on the endurance limit are possible.     

Topographie und elektrische Eigenschaften von InAs‐Quantenpunkten

Topography and electrical properties of InAs quantum dots Self assembled InAs‐islands were grown on GaAs with molecular beam epitaxy in the Stranski‐Krastanow growth mode. The topography of surface quantum dots was investigated by atomic force (AFM) and scanning electron microscopy (SEM). While the AFM enables to determine the dot height of ≈ 10 nm the SEM is best suited to study the lateral dimensions of uncapped islands. The latter technique gives a dot diameter of ≈ 30 nm. Although the size distribution of the islands is convoluted in the capacitance measurements on a dot ensemble, it was possible to determine roughly a Coulomb blockade energy of ≈ 20 meV for the ground state and ≈ 10 meV for the first excited dot level. Taking advantage of AFM‐lithography we were able to study electron transport through a single InAs island. Here we got a Coulomb blockade energy of 12 meV when electrons tunnel through the first excited state of the dot.