News Article | April 7, 2016
Researchers have developed a particularly flexible additive manufacturing method that allows them to produce bone implants, dentures, surgical tools or microreactors in almost any conceivable design. At the Medtec medical technology tradeshow in Stuttgart, Fraunhofer scientists will show their research results. The small pharmaceutical plant next to the patient’s bed is no bigger than a two-euro coin. With wires and channels that are just a few hundred micrometers wide, it constantly mixes various drugs — painkillers, blood thinners and antibiotics — and fine-tunes them to the patient’s current health condition. A futuristic scene of modern microreaction technology that doesn’t yet exist in hospitals. The Fraunhofer Institute for Ceramic Technologies and Systems IKTS in Dresden is working to change that in the near future. The researchers are focusing on suspension-based additive manufacturing methods and combinations of them with other manufacturing techniques to create not only microreactors, but also bone implants, dentures and surgical tools. At Medtec in Stuttgart from April 12 to 14, they will be presenting a technological solution for creating medical components in almost every conceivable design using additive manufacturing methods. “We have no limitations in terms of type or color of material for the target components. This allows us to process ceramics, glass, plastic or even metal using thermoplastic 3D printing. One more advantage is that several different materials can be produced at the same time,” says Dr. Tassilo Moritz from Fraunhofer IKTS’s “Materials and Processes” business division. In the lab, the scientists have already successfully made components out of high-performance ceramics and hard metals. Now, they are looking for partners to put their technology to real-world use. One area in which the multi-material approach is important is surgery: endoscopes frequently employ an instrument to first cut open tissue, and then quickly close the blood vessels back up again using electric current. To prevent electricity from shocking the patient, the instrument needs not only high-grade steel, but also insulated ceramic components. “Ceramic substances are often well-suited for medical devices and components. Ceramics are sturdy and can be cleaned thoroughly,” explains Moritz. Researchers arrived at their additive manufacturing method as a result of their expertise in ceramic materials and process technologies. The key to their technology lies in preparing optimum ceramic or metallic suspensions. The mixtures rely on a thermoplastic binder that becomes liquid at temperatures of around 80°C. This is a crucial point in additive manufacturing: it means the suspensions can quickly cool down, and one layer after another can be deposited in sequence. In this binder, they disperse powder particles of metal, glass or ceramics. “Our mixtures are very homogenous, and we precisely set the optimum level of viscosity. Only then can the printer put out the droplet size suitable for the particular component contour. Our mixtures can’t be too liquid or thick. To achieve this, we have to master the preparation technique,” says Moritz. The electrically generated temperature in the printer melts the suspension. After deposition, the droplets immediately harden as a result of the quick cooling process. The workpiece is then built up point by point on a flat platform. This allows different materials to be deposited at the same time via multiple application units. “Another challenge is adjusting the behavior of the different suspensions during the subsequent sintering of the components, to prevent any defects,” says Moritz. “To this end, we modify the initial powder through special grinding processes.” In sintering, finely grained ceramic or metallic substances are heated under pressure. The temperatures of the substances remain so low that the structure of the workpiece does not change. Moritz is hoping for great things from these new options for microreaction technology based on ceramic components. Until now, production technology has prevented a breakthrough in miniature chemical plants. Their use had previously been limited to research labs in the main. That could change: “We can now build ceramic components that fit the application instead of the production process,” says the materials scientist. “To date, ceramic microreactors have mostly been milled out of plates. Internal and external sealing have always been a technological challenge for this. And there has been the problem of making connections that fit. Now, we can just print them onto the ceramic component during manufacturing in whatever form.” This benefits not only doctors, but also pharmacists and chemists. In most cases, they are processing very expensive or hazardous substances. “It is more affordable and safer to first work with minimal quantities in a microreactor,” says Moritz.
News Article | October 23, 2015
The Jena research team and its innovative battery (from left to right): Prof. Dr. Ulrich S. Schubert, Tobias Janoschka und Dr. Martin Hager. Credit: Anne Guenther/FSU Sun and wind are important sources of renewable energy, but they suffer from natural fluctuations: In stormy weather or bright sunshine electricity produced exceeds demand, whereas clouds or a lull in the wind inevitably cause a power shortage. For continuity in electricity supply and stable power grids, energy storage devices will become essential. So-called redox-flow batteries are the most promising technology to solve this problem. However, they still have one crucial disadvantage: They require expensive materials and aggressive acids. A team of researchers at the Friedrich Schiller University Jena (FSU Jena), in the Center for Energy and Environmental Chemistry (CEEC Jena) and the JenaBatteries GmbH (a spin-off of the University Jena), made a decisive step towards a redox-flow battery which is simple to handle, safe and economical at the same time: They developed a system on the basis of organic polymers and a harmless saline solution. "What's new and innovative about our battery is that it can be produced at much less cost, while nearly reaching the capacity of traditional metal and acid containing systems," Dr. Martin Hager says. The scientists present their battery technology in the current edition of the renowned scientific journal Nature. In contrast to conventional batteries, the electrodes of a redox-flow battery are not made of solid materials (e.g., metals or metal salts) but they come in a dissolved form: The electrolyte solutions are stored in two tanks, which form the positive and negative terminal of the battery. With the help of pumps the polymer solutions are transferred to an electrochemical cell, in which the polymers are electrochemically reduced or oxidized, thereby charging or discharging the battery. To prevent the electrolytes from intermixing, the cell is divided into two compartments by a membrane. "In these systems the amount of energy stored as well as the power rating can be individually adjusted. Moreover, hardly any self-discharge occurs," Martin Hager explains. Traditional redox-flow systems mostly use the heavy metal vanadium, dissolved in sulphuric acid as electrolyte. "This is not only extremely expensive, but the solution is highly corrosive, so that a specific membrane has to be used and the life-span of the battery is limited," Hager points out. In the redox-flow battery of the Jena scientists, on the other hand, novel synthetic materials are used: In their core structure they resemble Plexiglas and Styrofoam (polystyrene), but functional groups have been added enabling the material to accept or donate electrons. No aggressive acids are necessary anymore; the polymers rather 'swim' in an aqueous solution. "Thus we are able to use a simple and low-cost cellulose membrane and avoid poisonous and expensive materials", Tobias Janoschka, first author of the new study, explains. "This polymer-based redox-flow battery is ideally suited as energy storage for large wind farms and photovoltaic power stations," Prof. Dr. Ulrich S. Schubert says. He is chair for Organic and Macromolecular Chemistry at the FSU Jena and director of the CEEC Jena, a unique energy research center run in collaboration with the Fraunhofer Institute for Ceramic Technologies and Systems Hermsdorf/Dresden (IKTS). In first tests the redox-flow battery from Jena could withstand up to 10.000 charging cycles without losing a crucial amount of capacity. The energy density of the system presented in the study is ten watt-hours per liter. Yet, the scientists are already working on larger, more efficient systems. In addition to the fundamental research at the University, the chemists develop their system, within the framework of the start-up company JenaBatteries GmbH, towards marketable products. Explore further: Agreement will lead to commercialization of redox flow batteries More information: Tobias Janoschka et al. An aqueous, polymer-based redox-flow battery using non-corrosive, safe, and low-cost materials, Nature (2015). DOI: 10.1038/nature15746
News Article | October 10, 2016
Fraunhofer IKTS reports that it has successfully 3D printed a range of hardmetal tools. The tools will be on show at WorldPM 2016 in Hamburg in October. High mechanical and chemical as well as a high temperature resistance and extreme hardness are required for tools that are used in mechanical and automotive engineering or in the construction and forming industry. The researchers at the Fraunhofer Institute for Ceramic Technologies and Systems IKTS in Dresden say that the tools produced with additive manufacturing (AM) have a ‘quality that is in no way inferior to conventionally produced high-performance tools’. Currently, cutting, drilling, pressing and stamping tools made of hardmetals are generally manufactured using uniaxial or cold isostatic dry pressing, extrusion and injection molding as well as by green shaping. In traditional tool manufacturing, complex geometries, such as helical or meandering cooling channels inside the component, are still implemented at high cost or not possible at all. Now IKTS scientists have succeeded in producing complex hardmetal tools via a binder jetting method. The starting powders or granules are locally wetted with an organic binder by a print head and bound. The challenge was to get 100% dense components, which have a perfect microstructure and thus good mechanical properties. By varying the metallic binder, bending strength, fracture toughness and hardness can be adjusted individually – the lower the amount of binder in the hardmetals, the harder the tool material. The prototypes manufactured at Fraunhofer IKTS have a binder content of 12 and 17% by weight and show a structure comparable to conventional routes. ‘Through the use of 3D printed complex green bodies which were subsequently sintered under conventional sintering conditions, we achieved components with a typical hardmetal structure and 100% density. Moreover, it is possible to get a homogeneous cobalt distribution, thus achieving a comparable quality to conventionally produced high-performance cemented carbide-based tools,’ said Johannes Pötschke, group leader at Fraunhofer IKTS. This story is reprinted from material from Fraunhofer, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.
News Article | December 1, 2015
Floating homes are becoming increasingly popular in Germany – not only as holiday homes, but also as permanent residences. The Lusatian Lake District (Lausitzer Seenland) is particularly suitable for such a lifestyle: with its 23 lakes and a surface area of over 32 000 acres, it is the largest artificial lake district in Europe. Over decades, the region, which is located between the German states Saxony and Brandenburg, had been characterized by open-cast lignite coal mining. In the coming years, this way of life of living on water will help enhance the region's attractiveness and boost its economy. This is also the objective of the Lusatian autartec project, which the two Fraunhofer Institutes based in Dresden, the Fraunhofer Institute for Transportation and Infrastructure Systems (IVI) and the Fraunhofer Institute for Ceramic Technologies and Systems (IKTS), are involved in, as well as other partners from the region such as medium-size companies, manufacturers, the Technical University of Dresden (TUD) and the Technical University of Brandenburg (BTU). They will all work hand in hand to build a floating home on Lake Geierswalde, to the northwest of the city of Hoyerswerda, by 2017. This floating home will not only look elegant, it will also be able to provide for its own water, electricity and heat. "These kinds of energy self-sufficient floating homes do not exist yet," says autartec project coordinator Professor Matthias Klingner of IVI. Many lakes in the Lusatian Lake District are cut off from infrastructure such as water and energy supply. "We want to find a solution for this kind of environment," says Klingner. Standing on a 13 by 13 meter steel pontoon, the house extends over two levels and offers 75 square meters of living space on the ground floor, and another 34 square meters on the first floor. A 15 square meter terrace overlooks the entire lake. The house combines modern architecture and structural engineering with state-of-the-art equipment and building facilities. For example, solar cells are integrated in the building envelope and lithium polymer batteries store the collected energy. In order to save space, the battey systems developed at IVI are integrated into the textile concrete walls or into the stair elements. Researchers at IVI are also working on the efficient provision of heating and cooling systems. A salt hydrate fireplace provides heat on cold winter days: above the fireplace there is a tub filled with water and salt hydrates. "When the fireplace is on, the salt hydrates liquefy and begin to absorb heat," Dr. Burkhard Fassauer of IKTS explains. When the salt hydrates are completely liquefied, the thermal energy can be stored almost indefinitely. In order to release the heat when required, radio-based technology is used to induce crystallization. The principle is known from pocket warmers: to induce crystallization, a metal disc inside is clicked so that the pocket warmer solidifies and gives off heat. When heated in water, the crystals liquefy and the heat is stored until the next click. However, a fireplace is not enough to heat the house during the winter. This is where a zeolith thermal storage unit in the pontoon can help: the zeolith minerals are dried during the summer – a purely physical process in which heat is stored. "In winter, the moist air is enough for the storage unit to give off heat," Fassauer explains. An adiabatic cooling system provides for cool air in the summer. Unlike conventional air conditioning systems, it does not require electricity but uses the principle of evaporative humidification to cool. A surface on the side of the house is landscaped and moistened and the process of evaporation then cools the building envelope. The experts at IKTS are responsible for the water supply in the houseboat. "We are currently developing and experimenting with a closed loop system for drinking and service water," Fassauer explains. To accomplish this, the scientists rely on a combination of ceramic membranes and various electrochemical and photocatalytic processes. Ashore, wastewater is usually treated using biological processes. This is not possible in a floating house. "We must rely on physical and chemical methods. Thus, ceramics provide very efficient ways to bring together processes like photocatalysis, electrochemistry and filtration in a confined space," says Fassauer. Other materials such as steel and plastic would fail in such aggressive processes. The equipment for the circulatory system will be accommodated in the pontoon. Explore further: University of Stuttgart gets a research house for solar heat storage
Clausner A.,Fraunhofer Institute for Ceramic Technologies and Systems |
Richter F.,TU Chemnitz
European Journal of Mechanics, A/Solids | Year: 2015
The aim of this paper is to investigate the possibilities of getting information on the initial yield stress Y from nano-indentation experiments with sharp indenters. Berkovich indenters have been used for the experiments and the data evaluation was performed by using two expanding cavity models (ECM) described in the literature, one for elastic-perfectly plastic, and one for power law work hardening materials. To characterize the ECMs, finite element simulations with extensive material parameter variations together with substantial experimental data are used. As a first result, the possibilities of determining Y using the introduced ECMs can be shown for the simulated materials (Fig. 3) and the presented selection of real specimens. Furthermore, the restriction of the ECMs to materials where the yield behavior obeys the von Mises yield criteria is discussed. In doing so it is shown that the indentation work, which can be determined directly from the indentation force-displacement curves, represents a useful quantity to assess the applicability of an ECM to a particular material. © 2014 Elsevier Masson SAS.
Comments on "an extended hardness limit in bulk nanoceramics" by J.A. Wollmershauser, B.N. Feigelson, E.P. Gorzkowski, C.T. Ellis, R. Goswami, S.B. Qadri, J.G. Tischler, F.J. Kub, R.K. Everett, Acta Materialia 69 (2014) 9-16
Krell A.,Fraunhofer Institute for Ceramic Technologies and Systems
Scripta Materialia | Year: 2014
The recently suggested validity of the Hall-Petch relationship for transparent spinel ceramics with grain sizes down to 28 nm is discussed here regarding the equivalence of grain size and indentation size effects. The quantitative characterization of the samples investigated as transparent needs a correction of the authors' calculation of the theoretical transmittance. For fundamental physical reasons, this theoretical transmission of ceramics with a cubic crystal lattice does not exhibit an intrinsic grain size influence. © 2014 Acta Materialia Inc.
Klemm H.,Fraunhofer Institute for Ceramic Technologies and Systems
Journal of the American Ceramic Society | Year: 2010
In this paper, a summary of the development of high-temperature silicon nitride (T>1200°C) is provided. The high-temperature capacity of various advanced commercial silicon nitrides and materials under development was analyzed in comparison with a silicon nitride without sintering additives produced by hot isostatic pressing. Based on this model Si3N 4 composed of only crystalline Si3N4 grains and amorphous silica in the grain boundaries the influence of various sintering additive systems will be evaluated with focus on the high-temperature potential of the resulting materials. The specific design of the amorphous grain-boundary films is the key factor determining the properties at elevated temperatures. Advanced Si3N4 with Lu2O3 or Sc 2O3 as sintering additive are characterized by a superior elevated temperature resistance caused by effective crystallization of the grain-boundary phase. Nearly clean amorphous films between the Si 3N4 grains comparable to that of Si3N 4 without sintering additives were found to be the reason of this behavior. Benefit in the long-term stability of Si3N4 at elevated temperatures was observed in composites with SiC and MoSi2 caused by a modified oxidation mechanism. The insufficient corrosion stability in hot gas environments at elevated temperatures was found to be the main problem of Si3N4 for application in advanced gas turbines. Progress has been achieved in the development of potential material systems for environmental barrier coatings (EBC) for Si3N4; however, the long-term stability of the whole system EBC-base Si3N4 has to be subject of comprehensive future studies. Besides the superior high-temperature properties, the whole application process from cost-effective industrial production, reliability and failure probability, industrial handling up to specific conditions during the application have to be focused in order to bring advanced Si3N4 currently available to industrial application. © 2010 The American Ceramic Society.
Schonecker A.J.,Fraunhofer Institute for Ceramic Technologies and Systems
IEEE International Ultrasonics Symposium, IUS | Year: 2012
The paper examines the development of piezoelectric multi-material-systems in view of smart light weight structures. It starts with an overview on piezoelectric transducer elements comprising monolithic units and composite elements. Next, approaches of integration into structural materials systems are considered, covering the aspects of design and adjustment to production technologies. Finally, future perspectives are highlighted. © 2012 IEEE.
Herrmann M.,Fraunhofer Institute for Ceramic Technologies and Systems
Journal of the American Ceramic Society | Year: 2013
Silicon nitride ceramics are used under conditions where high strength, hardness, and wear resistance are necessary. The increasing use of Si 3N4 ceramics in different environments demands an understanding of the relationships between microstructure and corrosion behavior. This study gives an overview of the behavior of silicon nitride in acids, bases, and hydrothermal conditions. It not only summarizes the literature data but also attempts to explain the mechanisms and to give some guidelines for the use of the materials in different environments. The stability of the ceramics against corrosion in acids and bases up to the boiling point is mostly controlled by the stability of the grain boundary. The stability can be predicted using the glass network theory. Materials with grain boundaries exhibiting a strong network, i.e., a high amount of SiO2 in the grain boundary, are stable in acids, but less stable under hydrothermal conditions and in basic solutions. Therefore, tailoring the grain boundaries can change the corrosion stability by several orders of magnitude. At temperatures above 200°C-250°C, the dissolution of the Si3N4 grains becomes a decisive factor determining the stability. © 2013 The American Ceramic Society.
Krell A.,Fraunhofer Institute for Ceramic Technologies and Systems |
Bales A.,Fraunhofer Institute for Ceramic Technologies and Systems
International Journal of Applied Ceramic Technology | Year: 2011
Most different transparent grades of sintered and single crystalline spinel were investigated by Vickers and Knoop tests with loads of 1 kg (HK1, HV1) and of 10 kg (HV10). The hardness ranking of all samples was HK1