Materials make a key contribution to the energy-efficiency of products
Materials are an important stepping stone on the journey to more sustainable process chains. Ceramics in particular are often underestimated, mainly because they are “invisible, but indispensable.” Experts at the Application Center for Sustainable Materials, Technologies & Processes, a Steinbeis Research Center, are systematically and methodically analyzing systems and technologies – as well as how such factors interact with one another. This is making it possible to work out research methods that should lead to sustainable, resource-saving, and energy-efficient processes and products.
Due to their special properties – such as resistance to high temperatures, corrosion, and wear and tear – ceramics are suitable for a wide range of applications. For example in the chemicals industry, ceramics are used as lining materials for gate valves; in wind turbines, ceramic hybrid bearings are making a contribution to the green energy transition. Under the German federal government’s hydrogen offensive, renewable energies will lay a foundation for future technologies such as electrolysis cells used in hydrogen production. High-performance ceramic materials are indispensable for fuel cells, as well as temperature-resistant thermal insulation in gas turbines.
Oxide ceramics are used in hydrogen production
Energy transition strategies therefore not only address the use of hydrogen in fuel cells, but also consider the transportation of energy in the form of hydrogen. It is therefore particularly important to produce green hydrogen. The technology required to make hydrogen is a solid oxide electrolysis cell. The role played by the electrolysis process is to decompose water into H2 and O2. The design and operating temperatures are equivalent to those of solid oxide fuel cells. The high operating temperatures of between 500 and 1,000°C therefore require solid electrolytes consisting of dense ionic conductors. An oxide ceramic made of yttria-stabilized zirconia (ZrO2 and Y2O3) is suitable for this purpose, due to its high melting temperature and high stability levels.
An essential factor with ceramics is temperature control during the firing and sintering process. This is important for determining material properties and defining product qualities in combination with the raw material. It is also central to forming materials, which involves high levels of energy. For this reason, it is important to save large amounts of energy in the manufacturing process. The challenge is to safeguard or even enhance the required product standards while at the same time lowering energy consumption. Using the example of yttrium-stabilized zirconia, this would mean that crystal structures can be set to cubic, tetragonal, or monoclinic by means of suitable process controls, cooling, and tempering processes, whereby desired or undesired quantity fluctuations can occur due to phase transformations.
It is therefore common to use higher firing and sintering temperatures in the manufacturing process to achieve good product quality. One way to optimize materials and improve sustainability is to regulate temperatures in the heating and cooling cycle. To make kiln processes more energy-efficient while maintaining the same or higher product quality, the method of choice is a holistic approach that involves modeling kiln processes and material properties in combination with applied material testing. High-performance ceramic materials are often subject to thermal shock during use, or they need to be highly resistant to thermal shock, so suitable material properties are required as a critical design feature of components. To assess the quality of optimized furnace processes, one suitable method is to evaluate thermal shock resistance in the produced ceramics. The challenge when doing this is that existing material testing methods for thermal shock resistance only provide qualitative information. It is not possible to apply such qualitative findings to simulation-based models used to design components or predict service life.
Modeling and simulation in material testing
What is the best way to come up with reliable material parameters in settings that closely resemble actual applications? To find out, the Steinbeis team led by Steinbeis Entrepreneur Prof. Dr.-Ing. Verena Merklinger from the Department of Mechanical Engineering at the HTWG Konstanz uses modeling and simulation (based on digital solutions) in combination with application-based material testing. Their aim is to design components and products with a strong focus on practical application, but also to optimize kiln processes to make them energy-efficient.
“The first step is to use modeling and simulation to plan and design test specimens for materials testing. This goes hand in hand with the use of fewer materials in order to optimize the design of test specimens, to invest less energy and effort in testing, and to cut development time. This targeted and efficient approach to test specimen design also optimizes material testing,” explains Verena Merklinger. The next step is to ascertain data and material properties by conducting material testing in scenarios that closely resemble actual applications and to feed this information into the simulation model, thereby optimizing it. Subsequently, material testing is repeated to validate the simulation model.
This iterative approach gradually improves the quality of the model, resulting in more accurate simulation models that are much more reliable. At the same time, this data lays a foundation for creating reliable designs and, based on this, upscaling to larger components. Transferring results to similar components also significantly shortens subsequent development times, underpinning material testing and the component design process with methods that are energy-efficient and save resources. This approach is also suitable for optimizing firing and sintering processes based on more energy-efficient temperature controls.
The Steinbeis Enterprise owns a thermal shock test rig which has been specifically designed to determine thermomechanical properties. Integrating the device into quality assurance processes makes it possible to improve the characterization and definition of the potential impact of changes on production processes. This approach also lays an important foundation for optimizing manufacturing processes, for example when lowering processing temperatures to save energy or when using hydrogen in furnace processes, changing temperature profiles but maintaining product quality requirements.
For the experts at Steinbeis, the project with VM&P marked the beginning of a partnership with an expert company in the modeling, simulation, and optimization of furnace processes. Material testing at the Steinbeis Research Center is based closely on actual application, adapted as required to the needs of each customer. The center also evaluates and interprets results in order to derive recommended actions.
Sustainability requires the holistic analysis of process chains
The oxide ceramics project highlights the fact that ceramics are essential for future green technologies. It also shows that sustainability affects the entire process chain, right through to quality assessment and materials testing. Adopting a systematic and holistic approach in order to take the entire process chain – including application – into account not only plays an essential role in the sustainability of ceramic materials, it is also important for metals, polymers, and composites. As a result, in addition to observing and assessing thermomechanical properties, an important part of sustainable systems and technologies is considering and analyzing stress imposed on component systems by corrosion and wear. The sustainability methods used by the experts at the Application Center for Sustainable Materials, Technologies & Processes are therefore not limited to materials, but also encompass and support innovation and development processes, including modeling and simulation in combination with applied materials testing.
Prof. Dr.-Ing. Verena Merklinger (author)
Steinbeis Research Center Application Center for Sustainable Materials, Technologies & Processes (Rennertshofen)