Project Overview

Legierungen auf Mo-Basis weisen vielversprechende mechanische Eigenschaften und Hochtemperaturbeständigkeit auf. In oxidierender Umgebung und Temperaturen oberhalb von 250 °C tritt allerdings aufgrund katastrophaler Oxidation unter Verflüchtigung des Molybdäns in Form des Oxids MoO3 Zerstörung des Werkstoffs auf. Diese Oxidationsprozesse können durch geeignete Schutzbeschichtungen zurückgedrängt werden, um den Werkstoff auch in oxidierender Atmosphäre bei erhöhter Temperatur einsetzten zu können. Das Vorhaben zielt auf einen bisher nicht beschriebenen Ansatz zur Aufbringung einer Zinkoxid-basierten Oxidationsschutzschicht auf Mo-Legierungen ab. Als Modellsystem soll TZM (Mo mit < 1 % Ti/Zr) verwendet werden, welches verbesserte (thermo)mechanische Eigenschaften im Vergleich zu reinem Mo, aber die gleiche Oxidationsproblematik aufweist. Zinkoxid, ZnO ist in der Lage, mit Mo-Oxiden zu reagieren und stabile ternäre Oxide wie ZnMoO4 oder Zn2Mo3O8 zu bilden. Die dem Vorhaben zu Grunde liegende Hypothese ist, dass diese ternären Zn-Mo-Oxide eine stabile und sauerstoffundurchlässige Schicht auf dem TZM-Substrat bilden und den Werkstoff somit vor Oxidation schützen. In Vorversuchen an ZnO-Mo-Tabletten hat sich dieses Konzept bereits als wirksam erwiesen und die Verbindung Zn2Mo3O8 konnte als Phase mit dem höchsten Potential für einen Oxidationsschutz identifiziert werden. Das Vorhaben gliedert sich in mehrere Abschnitte: Zunächst sollen die Reaktionspfade sowie geeignete Prozessparameter zur Synthese der Zielverbindung Zn2Mo3O8 ausgehend von ZnO, Mo und MoO2 aufgeklärt werden. Im Anschluss soll ein geeigneter Beschichtungsprozess zur Aufbringung Zn2Mo3O8-basierter Oxidationsschutzschichten entwickelt und angewandt werden. Als Methode ist eine an das Packzementieren angelehnte Reaktivbeschichtung von TZM-Substraten im ZnO-Pulverbett geplant. Die Mikrostruktur der erhaltenen Beschichtung sowie die Eigenschaften der Grenzfläche zum Substrat sollen dann mit den Parametern des Beschichtungsprozesses korreliert, und günstige Prozessparameter abgeleitet werden. Die erhaltenen TZM-Proben mit Zn2Mo3O8-Beschichtung sollen dann isothermen und zyklischen Oxidationsversuchen bis 1000 °C und 500 Stunden unterzogen werden. Daraus soll dann die Oxidationsschutzwirkung der Zn2Mo3O8-Beschichtung und die Oxidationskinetik abgeleitet werden. Zusammenfassend sollen alle Erkenntnisse in einem empirischen Modell zusammengefasst werden, welches eine qualitative Beurteilung der Oxidationsbeständigkeit von Zn2Mo3O8-beschichteten TZM-Substraten erlaubt.

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The replica or Schwartzwalder process is a widely used process in the industry for manufacturing cellular ceramics. It is based on a cellular template structure that is coated with a ceramic dispersion and thermally removed in the subsequent process. After the sintering process, a ceramic replica of the template remains.
Typically, open-cell polyurethane (PU) foams are used as templates, which can be produced cost-effectively and in large quantities. However, the options for customizing the template structure are very limited. Furthermore, PU foams - like all foam structures - have an irregular structure.
This is precisely where the project comes in: On the one hand, periodic, cellular structures are to be produced using additive manufacturing, and on the other hand, their geometry is to be specifically adapted to the respective application. In addition to the basic periodic structure (e.g. Kelvin cell, sodalite structure, gyroid structures, etc.), geometry parameters such as cell and window diameters, web thicknesses and web cross-section profiles are also to be adapted.
The additively manufactured templates can then be converted into a cellular ceramic with a corresponding structure using standard processes based on the replica process. The focus here is on the structural characterization of the final components, particularly with regard to their (web) porosity and the homogeneity of the coating or the web cross-section profile. A micro-computed tomograph is available for this purpose.
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The joint project of the OVGU Faculties of Electrical Engineering and Information Technologies (EIT), Process and Systems Engineering (VST) and Mechanical Engineering (MB) with NTUU Kiev-KPI and NTU Kharkiv-KhPI (in cooperation with DonNTU) is based on many years of cooperation between OVGU and the Ukrainian universities in Kiev, Kharkiv and Donetsk. In 2025 and 2026, the cooperation between the German and Ukrainian partners will be continued under more difficult conditions and its content will be further developed. This concerns the further compatibility of the Ukrainian partners' German-language degree programmes with the Bologna formats, but also the further linguistic qualification of lecturers and German teachers. For the former, the focus is on general language development, for the latter on specialist language development. To this end, specially prepared German lectures are offered for German teachers, internships (due to the war), courses to improve German language skills and specialist lectures for students are held online and students in Magdeburg are given the opportunity to attend specialist lectures. Some of the students on the relevant Master's degree courses in Magdeburg are working on their Master's theses.
Maintaining this cooperation is extremely challenging under the current conditions, particularly due to the significant restrictions on travel. However, the integration and continuous further development of online formats and offerings make it possible to maintain the cooperation under the current conditions.

Prof. Dr. Michael Scheffler
Otto von Guericke University Magdeburg
Faculty of Mechanical Engineering
Institute for Materials, Technologies and Mechanics
University Square 2
39106
Magdeburg
Phone: +49 391 6714596

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Adamantane-like compounds contain materials whose crystal structure can be derived from the adamantane base body or the structure of the diamond. Examples include ceramics such as SiC, AlN and ZnO, which all crystallize in the wurzite structure, the diamond lattice for binary compounds. The basic structure contains a tetrahedral environment for cations and anions. Due to the simple structure, the adamantane-like compounds have good phonon conductivity and, as a result, good thermal conductivity. Due to the large covalent bonding components, high temperatures and/or sintering additives are usually required for sintering these compounds.
Due to the complex composition of the ceramic raw material (base material + sintering aids), the formation of various secondary phases, for example Y-Al-O compounds in the system AlN-Y₂O₃, often occurs. These secondary phases significantly influence the properties of the base material. The phase evolution in the system AlN-Y₂O₃ is well studied, while for the system ZnO-Sb₂O₃-Bi₂O₃ phases of unknown structure often occur. At the same time, the phase equilibria are fundamentally influenced by the presence of other metal cations as dopants. Therefore, the investigation of the phase composition by means of powder diffraction is one focus. Another focus is the investigation of the structural-chemical influence of dopants introduced into corresponding secondary phases. This also includes the structural characterization of unknown phases - if purely representable - on the basis of data obtained from powder X-ray diffraction. These investigations are supported by quantum chemical (DFT) calculations.
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The current situation shows that new solutions and technologies need to be used in the development and production of electrical heating elements as the requirements for precise temperature control, service life and functionality increase. The use of new materials and the reliable production of heating elements made from these materials are of particular importance. Progressive miniaturization in the field of (plastic) injection moulding is constantly increasing the demands on the heating elements used in terms of compactness and resistance to temperature, erosion and moisture. As a result, heating elements with small diameters (less than 1.5 mm) are becoming increasingly important. For the reasons mentioned above, the aim of the research project is to
Development of a technology for the production of a new moisture-insensitive heating element using novel potting compounds made of polymer-derived ceramics (PDC) using investment materials based on MgO.
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Product quality requirements are becoming increasingly stringent. For products whose manufacture includes heat treatment steps, this means, among other things, mastering precise temperature control, but also adapting the heating elements used to the process in such a way that they have a long service life, high functionality and a low functional loss rate. In addition, there are issues of progressive miniaturization, e.g. in the field of (plastic) injection moulding, which expands the catalog of requirements for such heating elements in terms of their compactness, but also with regard to temperature, erosion and moisture resistance. In this context, heating elements with diameters of around 1.5 mm and in the working temperature range below 500 °C play a special role.
The aim of the project is therefore to develop a completely new, moisture-impermeable material based on pre-ceramic formulations and an investment material that is less sensitive to moisture, and to integrate the application into the existing heating element production process.
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This joint project between the faculties of the OVGU engineering campus (FEIT, FMB and FVST) with NTUU Kiev-KPI and NTU Kharkiv-KhPI (in cooperation with DonNTU) builds on many years of cooperation between OVGU and the Ukrainian universities in Kiev, Kharkiv and Donetsk. In 2023 and 2024, the cooperation between the German and Ukrainian partners was continued under difficult conditions and further developed in terms of content. This involved making the Ukrainian partners' German-language courses of study more compatible, but also the further linguistic qualification of lecturers and German teachers; for the former, the focus was on general language development, for the latter on specialist language development. To this end, specially prepared German lectures were offered for German teachers, internships (due to the war) were converted into online formats, courses were offered to improve German language skills, specialist lectures were held online for students and students in Magdeburg were able to take part in specialist lectures. Some of the students on the relevant Master's degree courses in Magdeburg completed Master's theses, which were successfully defended. This also made it possible to maintain some of the established research collaborations with Kiev and Kharkiv.
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This joint project between the faculties of the OVGU engineering campus (FEIT, FMB and FVST) with NTUU Kiev-KPI and NTU Kharkiv-KhPI (in cooperation with DonNTU) builds on many years of cooperation between OVGU and the Ukrainian universities in Kiev, Kharkiv and Donetsk. In 2023 and 2024, the cooperation between the German and Ukrainian partners was continued under difficult conditions and further developed in terms of content. This involved making the Ukrainian partners' German-language degree courses more compatible, as well as the further linguistic qualification of lecturers and German teachers; for the former, the focus was on general language development, for the latter on specialist language development. To this end, specially prepared German lectures were offered for German teachers, internships (due to the war) were converted into online formats, courses were offered to improve German language skills, specialist lectures were held online for students and students in Magdeburg were able to take part in specialist lectures. Some of the students on the relevant Master's degree courses in Magdeburg completed Master's theses, which were successfully defended. This also made it possible to maintain some of the established research collaborations with Kiev and Kharkiv.
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As part of the DFG joint project launched in 2020, complex, multifunctional oxidation protection coating systems were developed for the material protection of molybdenum (Mo)-containing refractory metal alloys. Such alloys exhibit higher thermal stability than the nickel-based superalloys previously used as turbine materials. With sufficient long-term stability, they could therefore be operated in turbine applications at temperatures 150 K higher, which would result in an increase in turbine efficiency. However, the oxidation of Mo and the evaporation as Mo oxide are proving to be a problem, which inevitably leads to the mechanical disintegration of a corresponding component and requires protective coatings of a few tens to a few hundred micrometers thick, preferably with a self-healing function to prevent cracking in the coating.
Such a coating system, consisting of a so-called preceramic polymer - an oligomeric chemical compound that can be converted into a ceramic by heat treatment -, particulate fillers such as silicon, boron and hexagonal boron nitride, was tested in long-term oxidation experiments and shows promising properties on selected Mo-containing alloys.
As the layer thicknesses cannot be extended indefinitely, a supplementary application was submitted to the above-mentioned application in order to combine the coating process based on filled preceramic polymers with the so-called pack cementation process - a coating process in which protective components such as boron and silicon are applied from the powder bed using transport agents via diffusion processes in the gas phase - and thus a) to further increase the layer thicknesses and b) the effectiveness of the protective layers obtained. Initial results are promising and show that it is possible to combine both processes to produce oxidation protection coatings with thicknesses of more than one hundred micrometers. The work on combining both processes is being systematically investigated as part of a Walter Benjamin Research Fellowship funded by the DFG.
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The 8^th International Conference on Cellular Materials – CellMAT 2024 – organized under the conference chair Michael Scheffler, together with six co-chairs from Germany and 21 program committee members from all over the world and hosted by the Deutsche Gesellschaft für Materialkunde e. V. (DGM), was held from 27-NOV-2024 to 29-NOV-2024 in Magdeburg, Germany, in the Fortress Mark. Almost 70 participants from academia, institutes and industry from 13 countries took part in this international event and reported on current research results on cellular materials of all classes. The total of 54 contributions included 4 keynote lectures, 4 invited lectures and seven posters. The opening lecture was given by the renowned metallurgist and materials scientist Christos Aneziris from the Technical University Bergakademie Freiberg, Saxony. The next CellMAT is expected to be held in spring 2027.

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The work focuses on the development and characterization of novel multiphase high-temperature materials based on a Mo solid solution phase (Moss) reinforced with intermetallic Mo2ZrB2 and Mo2HfB2 phases with high melting points. Mo-Hf-B and Mo-Zr-B are a class of high-temperature materials that can find various applications, e.g. in the aircraft industry due to their high creep resistance at the targeted application temperatures, which is superior to modern nickel-based superalloys. However, the material behaviour in the medium temperature range is critical; here the molybdenum oxidizes, which makes material protection necessary.
As part of a sub-project, self-healing coating systems are being developed, characterized and tested in an application-oriented manner. These coating systems consist of an oxygen-free preceramic polymer and oxygen-binding filler particles such as Si and B. The conversion into a closed ceramic protective layer takes place in an inert atmosphere in the temperature range between 800 °C and 1200 °C.
Cyclic oxidation tests prove a protective effect (still to be improved) of the coating in the temperature range between 800 °C and 1000 °C; the effect at higher temperatures is currently being investigated.
Initial results of radiographic investigations show that a zirconium molybdate phase is formed by adding ZrO2 as an additional filler, i.e. the alloy components Mo react to form stable phases and remain in the sample; the evaporation of Mo oxides is largely prevented. The role of the protective layer in this process has not yet been fully clarified and is the subject of further investigations.
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Cellular ceramics are of great importance in the metalworking industry as a filter medium for molten metals in foundry processes. The Schwartzwalder or replica process is the state of the art for the production of these ceramic foams. The basis is the application of a ceramic dispersion to a polymer foam template, followed by burning out the template and sintering the green body. The resulting ceramic foams are characterized by cavities in the web material resulting from the burnout of the template structure and longitudinal cracks in the webs resulting from the incomplete coating of the template. These cavities and cracks offer the potential for functionalization of the cellular ceramic, for example by loading with active species, but also limit the mechanical stability of the structure.
There are isolated, qualitative descriptions of the formation of cracks in the bar material in the literature, which take into account factors such as the wetting of the polymer template as well as thermal expansion and gas development during the template burnout. However, a systematic investigation of the effects, which also includes the shrinkage of the web material, is lacking.
The aim of the project is to investigate the hollow web structure - on the one hand in simplified model systems and on the other hand in cellular structures - as a function of the sintering temperature. Polymer rods with different cross-sectional profiles are used as model systems, which can be coated with ceramic dispersion in a very defined way by dip coating. Model materials are common engineering ceramics such as alumina or zirconia. The samples - model bridges as well as cellular ceramics - are primarily examined using micro-computed tomography. This method allows the precise analysis of material thickness and cavities in the examined structures. The final aim of the project is to develop a model that can be used to predict the hollow web volume on the one hand, and the frequency and dimension of longitudinal cracks in the web material on the other, as a function of the sintering temperature for a ceramic material of known shrinkage. This allows the process optimization for the production of replica foams - both with regard to an improvement in strength (avoidance of cracks) and with regard to a hollow web functionalization (control of the hollow web accessibility).
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Adamantane-like compounds contain materials whose crystal structure can be derived from the adamantane matrix or the structure of diamond. Examples are ceramics such as SiC, AlN but also ZnO, which all crystallize in the wurzite structure, the diamond lattice for binary compounds. The basic structure contains a tetrahedral environment for both cations and anions. Due to the simple structure, the adamantane-like compounds have good phonon conductivity and, as a result, good thermal conductivity. Due to the large covalent bond fractions, high temperatures and/or sintering additives are usually required for sintering these compounds. With the exception of SiC, hardly any cellular ceramics have been produced from these materials to date.
The aim of the project is the production and characterization of cellular ceramics - primarily from the adamantane-like compounds AlN and ZnO. This includes the development of suitable dispersions for the application of the Schwartzwalder process as well as the selection of suitable sintering additives and sintering conditions. The foams obtained will then be characterized with regard to their microstructure and properties (thermal conductivity, mechanical properties).
Due to the complex composition of the ceramic raw material (base material + sintering aids), the formation of various secondary phases, for example Y-Al-O compounds in the system AlN-Y₂O₃, often occurs. These secondary phases significantly influence the properties of the base material. The phase evolution in the system AlN-Y₂O₃ is well studied, while for the system ZnO-Sb₂O₃-Bi₂O₃ phases of unknown structure often occur. Therefore, the investigation of the phase composition in the ceramic web material of the foams produced using the powder diffraction method is a focal point. This also includes the structural characterization of unknown phases - if purely representable - on the basis of data obtained from powder X-ray diffraction.
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High-temperature resistant Mo-Si-B materials are being intensively investigated as suitable substitutes for nickel-based materials. A known problem with these materials is their oxidation behavior. The Mo solid solution phase in particular oxidizes catastrophically depending on the temperature, forming a volatile Mo oxide. Previously known protective coating systems have not been able to solve this problem satisfactorily. The aim of the project is to develop a new protective system based on preceramic polymers containing fillers with high oxidation resistance.

As part of the sub-project, oxidation protection coating systems based on preceramic polymers of the polysilazane type with oxygen-absorbing filler particles (Si, B, silicides) are being developed and tested in application-oriented oxidation tests with regard to their protective effect. In addition to a perhydropolysilazane, promising compositions contain 25 % silicon and 15 % boron by volume; both fillers form a low-viscosity glass under oxygen absorption, which is able to close microcracks in the coating system and on the material surface to be protected. Modifications of the protective coatings are currently being carried out with the filler boron nitride. Oxidation tests of the coated refractory metal alloys pyrolyzed at 1000 °C in nitrogen show very good oxidation protection at 800 °C, which showed no further changes in mass over the test period of 100 hours after an initial increase in mass, thus indicating a high protective effect.
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The availability of novel MATERIALS is a key issue for technical innovations, e. g. in energy conversion, mobility or medical engineering. While the effort of R & D in developing new materials was immens over the last years, there is a lack in a detailed understanding of the materials´ behaviour like in complex mechanical stress situations or when exposed to high temperature or radiation. This holds for compact as well for cellular materials.
In order to bridge this gap an integrated approach will focus on the combination of materials processing, materials design, complex stress situations in materials and mathematical modelling. While several of these categories are already combined to each other, R & D of holistic approaches is still in the beginning, and the challenge is to develop connected models which describe the process-microstructure-properties-relationships of materials of different provinience and porosity. Only such a combined approach will allow feedback between materials design and materials behavior.
PhD students in materials science and technology will have the opportunity within a four-year track to work with modern processing technologies and high-tech characterization methods such as state-of-the-art scanning electron microscopy, biaxial testing equipment and several in situ and combined methods. A four-year track is intended.

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Due to their outstanding properties metallic cellular structures have increasingly come into focus of research and development. A great number of potential applications has yet been addressed, not least including the utilisation for the purpose of structural support as well as applications in the fields of light-weight construction or biomedicine.

However, the specific surface area of those structures is commonly too small. Moreover, cellular structures may cause mechanical instabilities of materials if critical heigths or diameters are exceeded. To bridge this gap, novel manufacturing strategies have to be developed and transferred to common materials.

The objective of this sub-project is to develop a novel processing route in order to produce mechanically stable, high-surface area cellular metals. The development of "process-microstructure-properties" relations is essential for the understanding of the material's behaviour.

Solid state microstructure and mechanical characterisation, non-destructive and application-related testing, as well as collaborations with our partners of the materials simulation group make up integral parts of this sub-project.

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The use of renewable raw materials to generate energy and heat is also becoming increasingly important due to the urgent need to reduce CO2 emissions. In particular, the area of energy generation from biomass, including pellet combustion, is recording high growth rates. The current widespread use of biomass to generate energy through low-temperature combustion has significant disadvantages such as the production of CO, dioxins and toxic components. The lack of options for controlled combustion at high temperatures has so far prevented energy-efficient plants.
The aim of the project is to develop a new combustion chamber for low-emission high-temperature pellet combustion systems made from a new ceramic SiC-based composite material and a new technology for manufacturing this composite material. With dynamically controlled high-temperature combustion above 1,350 °C in newly developed combustion chambers, low-emission combustion with high efficiency is now possible. The material price for SiC-based products is to be reduced by 50 % and the thermal conductivity of the combustion chambers increased by at least 300 %.
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Background
Ceramic foams produced by the replica technique have many advantages due to their structure and material properties, but have a comparatively small surface area (compared to, e.g., fixed-bed reactor fillings). Furthermore, the potential of the production-related hollow strut was found to be expandable.

Objective
>> Increase of the actively usable surface of replica ceramic foams while maintaining the mechanical strength

Methods
Replica technique, sacrificial materials, Sol-gel-alumina powder, demixing, freeze casting

Results
Through a combination of replica process and freeze processing, ceramic foams with at least doubled proportion of open strut porosity and a compressive strength around 1 MPa were produced.
The prepared specimens (total porosity ~ 90%), were extensively characterized in terms of strut porosity, width of pore and material lamellae, pore volume, object-surface to object-volume ratio and compressive strength. The most important process parameters for achieving stable and highly porous foams were identified as freezing temperature, solid content and amount of thickening agent.
In addition, it was shown that the foam supports, which contained additional pores, can be coated with a high load of zeolite MFI.

Conclusions
The newly developed process has expanded the application range of replica ceramic foams, as the disadvantage of a comparatively small surface area was eliminated while maintaining sufficient mechanical strength.

Orignality
To the best of our knowledge, this approach has not been performed or studied in detail by anyone else in the way presented here.
The contribution of the work is seen as very profitable in terms of the use of replica ceramics as supports for active materials, for example, in catalysis applications.

Keywords
replica technique, ice templating, freeze casting, alumina foams, hierarchial porosity, zeolites

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The aim of this project is to develop a coating system to build up complex functions for the effective component protection of Mo-Si-B alloys; this system consists of an oxygen-free preceramic polymer of the polysilazane type that can be processed in air and filled with ceramic and/or metallic particles. The fillers have three functions: to increase the coating thickness compared to the unfilled coating system; to reduce the shrinkage of the coating material caused by the transition from polymer to ceramic; and to form new phases by reaction between the preceramic polymer, filler and component(s) and the service atmosphere, which should compensate for a possible volume change due to abrasive/oxidative processes on the (coated) component surface (volume expansion of the fillers when oxygen is absorbed). Phase analysis, composition and state are determined using X-ray diffraction (XRD; Rietveld analyses are carried out if there are significant proportions of crystalline phases).
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Ziel dieses Projektes ist die Entwicklung eines Beschichtungssystems zum Aufbau komplexer Funktionen für den effektiven Bauteilschutz von Mo-Si-B-Legierungen; dieses System besteht aus einem sauerstofffreien präkeramischen Polymer vom Polysilazantyp, das sich an Luft verarbeiten und mit keramischen und/oder metallischen Partikeln füllen lässt. Die Füllstoffe haben drei Funktionen: die Erhöhung der Schichtdicke im Vergleich zum ungefüllten Beschichtungssystem; die Reduzierung der durch den Übergang vom Polymer zur Keramik bedingten Schwindung des Schichtwerkstoffs und die Bildung neuer Phasen durch Reaktion zwischen präkeramischem Polymer, Füllstoff und Komponente(n) und der Serviceatmosphäre, die eine mögliche Volumenänderung durch abrassive/oxidative Prozesse an der (beschichteten) Bauteiloberfläche kompensieren sollen (Volumenausdehnung der Füllstoffe bei Aufnahme von Sauerstoff). Phasenanalyse, -zusammensetzung und -zustand werden mittels Röntgendiffraktometrie erfasst (XRD; bei Vorliegen nennenswerter Anteile kristalliner Phasen werden Rietveld-Analysen durchgeführt).

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The work deals with the targeted adjustment of the surface properties of ceramic foams. The variation from hydrophilic to hydrophobic opens up new application possibilities for cellular ceramics, for example in chemical process engineering in the field of mass transfer. As part of the project, ceramic foams with different surface energy and wettability are being developed as reactor internals and investigated in multiphase, immiscible systems with a focus on the mass transfer efficiency of the phases involved.
The surface properties of the open-pored ceramic foams are specifically adjusted by coating them with polysiloxanes, whose surface chemical and physical properties can be adjusted by heat treatment (temperature, time, atmosphere). This allows the wetting with fluid media of different polarities to be influenced. The change in the contact angle between the foam surface and the fluid medium serves as a measure of wetting, for which comparative tests are carried out on planar, concave and convex reference samples and attributed to the properties of the curved surfaces of the foam webs.
The application-oriented testing of the foams is carried out using liquid-liquid reactive extraction as a static mixer and its influence on phase dispersion. Depending on the surface properties of the cellular materials, the foam structures are intended to intensify phase dispersion. The figure shows the schematic structure of the liquid-liquid extraction system with the ceramic foams as mixer inserts.
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Ceramic foams are used in numerous technical applications, e.g. as molten metal filters, as thermal insulation or as bone replacement materials. The process-related hollow structure of their webs leads to a comparatively low mechanical strength.
In order to increase the strength of oxide ceramic foams, novel multiple coating and infiltration strategies with particulate and molecular precursors and their consolidation in the ceramic foam were developed. It was shown that both the infiltration and coating of aluminum oxide and the infiltration and thermal conversion of zirconium-containing compounds have a positive effect on the mechanical strength of ceramic foams without significantly influencing the porosity. In [1] it was shown that the strength of ZTA foams can be increased by infiltration to 2.66 MPa at a porosity P of 86 % and by multiple coating to over 11 MPa (P = 59 %).

References
[1] X. Chen, U. Betke, S. Rannabauer, P. Peters, G. Söffker, M. Scheffler, Improving the strength of ZTA foams with different strategies - immersion infiltration and recoating; Materials 10 (2017) 735.
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High-temperature resistant Mo-Si-B materials are being intensively investigated as suitable substitutes for nickel-based materials. One problem with these materials that has not yet been solved is their oxidation behavior. The Mo solid solution phase in particular oxidizes catastrophically depending on the temperature, forming a volatile Mo oxide. It has not yet been possible to solve this problem with known protective coating systems.
The aim of the project is to develop a new type of active protection system based on preceramic polymers and fillers. To this end, a material concept is being developed in which oxygen from the working atmosphere is absorbed by a protective layer and reactively converted into a component of a diffusion protection layer, which in turn significantly reduces oxygen diffusion in the direction of the metal surface to be protected.
In addition to developing the coating and material system and gaining an understanding of its operating principle, the investigations also include application-related studies on the protective effect in oxidizing (working) atmospheres. The project is being carried out in cooperation with Prof. Dr. Manja Krüger, RWTH Aachen University. Initial investigations into reaction pathways and the protective effect have been very promising and have been published in [1].

References
[1] I. Smokovich, Georg Hasemann, Manja Krüger, Michael Scheffler, Polymer derived oxidation barrier coatings for Mo-Si-B Alloys; Journal of the European Ceramic Society 37 (2017) 4559-4565.
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The BMBF junior research group NEOTHERM deals with the production of novel functional materials based on ceramic foams with active layers of microporous compounds (zeolites, metal-organic framework compounds) for sorptive energy storage or for heat pump applications. Current work focuses on the development/further development of cellular metallic and ceramic carrier materials with large and, above all, accessible surfaces and their coating with metal-organic framework compounds (MOFs) as active components. Direct crystallization processes and conventional coating processes are being investigated.

The main issues in carrier development are increasing the thermal and electrical conductivity of the web material, optimizing the pore geometry for mass transport and functionalizing the carrier surface for the best possible bonding of the active layer. For the latter point, trialkoxysilanes have proven their worth, and it has been possible to apply well-bonded active layers of the MOFs MIL-101(Cr), UiO-66(Zr) and HKUST-1 to Al₂O₃ and SiC foams.
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The interdisciplinary junior research group Novel Composite Materials for Thermochemical Energy Storage (NEOTHERM) develops, characterizes and evaluates micro-macro-porous composite materials for thermochemical energy storage. The aim is to provide sorption materials for the sorbate water with high storage density, effective heat transfer and application-adapted sorption temperature ("20-500 °C) and suitable temperature range both for the storage of solar heat and for energy recovery from technical processes. To this end, cellular materials are to be developed as carrier materials and optimized with regard to their chemical, morphological and thermal properties. In parallel, microporous crystalline compounds (metal organic frameworks = MOFs and zeolites) are to be developed and/or modified as active components of heat storage and fixed to the carrier, e.g. by means of in-situ crystallization or carrier-linker reaction. The junior research group will work on the following aspects of the new material composites: (1) Synthesis of new or (2) Development of manufacturing processes for macroporous monolithic materials with variable surface chemical and thermal properties and specifically adjusted, open porosity (carrier), (3) Coating/surface modification of open-cell foams to adjust the sorption properties of the composite material, (4) Control of adsorption and desorption processes in porous solids by controlling the pore size and shape, (5) Evaluation of the long-term behavior of the heat storage materials. The development of the new materials is carried out from the outset with a view to their technical application in terms of working temperature, charging/discharging behavior, long-term stability, storage density, costs and safety.

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High-performance ceramics are used in a variety of industrial applications due to their special range of properties (high temperature resistance, wear resistance and hardness). However, with an inherently low crack toughness, there is a malus in terms of reliability for technical use.
The crack toughness can be increased by adding reinforcing phases. Carbon nanotubes (CNTs) have this property, but homogeneous distribution of commercially available CNTs in ceramic matrices is time-consuming and energy-intensive.
In a novel approach, CNTs are formed in the presence of a transition metal catalyst during the conversion of a preceramic polymer into a polymer-derived ceramic. The hydrocarbons released during the conversion and coming into contact with the catalyst are used to form CNTs in situ. Thus, CNT-containing ceramics can even be produced in a hydrocarbon-free atmosphere, bypassing the problems mentioned above.
The CNT-containing ceramics are ground in a second process step and compacted using a field-assisted sintering process. The temperatures are typically around 1600 °C in order to obtain compact, almost pore-free ceramics. This in turn leads to a process known as carbothermal reduction, whereby the CNTs are partially converted into SiC. In order to achieve a reduction of the sintering temperature below the starting temperature of the carbothermal reduction, further additives and nanoparticulate fillers were introduced into the preceramic polymer. It was shown that the sintering temperature for producing a compact ceramic can be lowered by more than 150 °C and thus the carbothermal reduction can be largely suppressed. This results in compact bodies with a significantly higher theoretical density compared to their boron-free counterparts, which also have significantly higher strengths due to their lower porosity.
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Ceramics are used in many industrial applications due to their temperature resistance, wear resistance and hardness. However, they have a naturally low crack resistance. This is an obstacle to many applications.
Crack resistance can be increased by adding a reinforcing phase with a high aspect ratio. Carbon nanotubes (CNTs) have this property, but they are expensive and can only be incorporated homogeneously into ceramic materials at great expense.
In a completely new approach, CNTs are formed in the presence of a transition metal catalyst during the conversion of a preceramic polymer into a polymer-derived ceramic. The hydrocarbons released during the conversion and coming into contact with the catalyst are used to form CNTs in situ. In this way, CNT-containing ceramics can be produced without the need for hydrocarbons in the process gas. This process can also be used to produce CNT coatings, e.g. on carbon fibers. The high porosity of this composite material made of polymer-derived ceramic and the CNTs after the first process stage is then largely eliminated by field-active sintering; the advantage of this process is the short process time at high temperatures, which allows the CNTs to retain their structure and bond to the polymer-derived matrix. This results in significantly higher fracture toughness.
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Negative thermal expansion materials are developed on the basis of preceramic polymers that are loaded with fillers with a negative coefficient of thermal expansion (NTE) and converted into polymer-derived ceramics in a downstream heat treatment (pyrolysis). The NTE materials used are β-eucryptite and zirconium tungstate. The knowledge gained about the properties of the completely new material is used in the development of coatings, whereby the layer formation takes place via a dip coating process.

The large difference between the expansion coefficients of the two material components leads to residual stresses in the composite material, which cause cracking and pore formation. Using numerical simulation, these stresses between the matrix and particle material can be quantified and their influence on the mechanical properties of the resulting material can be estimated.
           
SEM image of a composite material with 50 % by volume β-eucryptite, after pyrolysis at 800 °C (left) and results of the simulation of stress distributions (right)
If the production of stable NTE layers on high-temperature stable materials is successful, such systems can lead to new applications in temperature-stressed components where, for example, heat flow plays an important role.
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Corrosion processes lead to immense economic damage every year, estimated at around USD 8 billion. Effective corrosion protection can be achieved using numerous coating processes. One of these comparatively new processes makes use of preceramic polymers in combination with ceramic and/or metallic fillers. The advantage lies in the use of comparatively inexpensive coating application processes such as spray, dip or centrifugal coating and the ability to coat even geometrically complex workpieces. The conversion of the (filler-containing) preceramic polymer layers into ceramic layers takes place in the temperature range from 800 °C to 1400 °C.
To protect titanium alloys, a perhydropolysilazane (PHPS) filled with SiC, h-BN, TiSi₂+B or Si₃N₄ was applied to Ti-6Al-4V by dip coating, pyrolyzed in argon at temperatures below 1000 °C and then subjected to a corrosion test at 800 °C for 80 hours. Some of the coatings showed slight changes in mass or high resistance to corrosion.
These current results form the basis for investigations into the individual reaction steps during oxidation and oxidation protection. Follow-up investigations are initially dedicated to thermodynamic considerations and finally to the experimental further development of protective coatings based on preceramic polymers.
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The aim of the work is to develop a new type of ceramic material based on preceramic polymers. In addition to reduced porosity and increased strength, the new material should above all have significantly higher crack resistance. This is to be achieved by introducing carbon nanotubes (CNTs) into the ceramic matrix. In a novel approach, CNTs are to be formed directly during the thermal conversion of preceramic polymers in the matrix material in the presence of a transition metal catalyst and bonded to the matrix in a second process step by field-assisted sintering. The microstructure of the nanocrystalline material should be retained, which leads to a significant increase in crack toughness compared to CNT-free materials.
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Innovative start-ups through a closed process chain for the production of cellular materials and components The installation of an incubator is intended to give students, graduates, scientific staff at OvGU and employees of other scientific institutions in the state of Saxony-Anhalt the opportunity to understand the entire process chain for the production of cellular ceramics and glasses for the first time, from component design and assembly to the non-destructive, three-dimensional characterization of the finished product in all steps.
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Ziel des Vorhabens ist die Herstellung von polymeren und keramischen, strukturierten Beschichtungen mit großer spezifischer Oberfläche auf Metall- und Keramiksubstraten. Die Schichten werden aus Si-organischen Polymer-Lösungsmittel-Systemen generiert. Die Strukturierung der Schichten erfolgt über Entmischungs- und Entnetzungsprozesse zwischen organischer Lösungsmittel- und Si-organischer Polymerkomponente, die zu netzartigen Strukturen führen. Das Verhältnis von unbeschichteter zu beschichteter Fläche, die Schichtdicke und die Morphologie der Strukturen werden dabei über chemische und physikalische Eigenschaften des Systems, die Schichtdicke und die Trocknungsbedingungen gesteuert. Die Erkenntnisse zur Strukturbildung als Funktion von Polymereigenschaften, Zusammensetzung und Prozessparametern dienen der Beschreibung der Zusammenhänge bei der Strukturbildung.

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Präkeramische Polymere bieten bei der Herstellung von Keramiken gegenüber konventionellen Prozessrouten zahlreiche Vorteile wie z. B. die Nutzung von Formgebungsverfahren aus der Kunststoffverarbeitung, die stufenlose Einstellung von Eigenschaftsprofilen oder die thermische Umwandlung bei vergleichsweise niedrigen Temperaturen. Diese Vorteile werden bei der Bearbeitung dieses Projekts genutzt. Ziel ist zunächst, die chemischen Reaktionen zwischen präkeramischen Polymeren vom Polysiloxantyp mit partikulären Tantal-Füllstoffen (Ta, TaC) und die resultierenden Komponenten der entstandenen Kompositkeramiken zu identifizieren und die neuartigen Werkstoffe zu charakterisieren. Die Ergebnisse aus diesen Untersuchungen bilden die Grundlage zu weiterführenden Untersuchungen für Ta-haltige Schichten auf Hochtemperaturwerkstoffen, die mittels einfacher Verfahren (Tauchbeschichtung, Sprühbeschichtung) appliziert werden.

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Gesamtziel des Verbundprojekts ist es, einen Hochtemperatur-Rekuperator mit verbesserter Wärmeübertragung auf Basis keramischer Füllungen zu entwickeln. Für die Erreichung dieses Zieles werden a) keramische Funktionsschutzschichten entwickelt, die eine Reaktion zwischen Rekuperatorwerkstoff und Rahmenwerkstoff selbst bei hohen Temperaturen unterbinden, b) Auslegungen für ein neuartiges Rekuperaturdesign durchgeführt und c) Funktionsmuster aufgebaut und unter Einsatzbedingungen getestet. Die Energieeffizienz der Funktionsmuster soll durch Erhöhung der Einsatztemperaturen über den gegenwärtigen Stand der Technik der Luftvorwärmung in Rekuperatoren deutlich hinausgehen.
Zur Erlangung dieses Gesamtziels hat sich ein Konsortium zusammengefunden, das unter Verknüpfung der Ergebnisse und Verzahnung der Arbeiten die folgenden Teilaufgaben bearbeitet:
Entwicklung einer Wärmeübertragerwerkstoff-Schutzschicht (Teilprojekt I), Entwicklung einer Gehäusewerkstoffschutzschicht (Teilprojekt II), Auslegung des Rekuperators, Testung und Funktionsmuster (Teilprojekt III) sowie Entwurf, Bau und Testung des Funktionsmusters (Teilprojekt IV).
Durch Erhöhung der Arbeitstemperaturen auf über 1000 °C wird eine deutliche Erhöhung der Energieeffizienz, verbunden mit einer drastischen Reduzierung der CO2-Emissionen bei thermischen Prozessen mit Wärmerückgewinnung erwartet.

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Ziel des Vorhabens ist die Herstellung von polymeren und keramischen Mikro- und Nanohohlkugeln mit enger Durchmesser- und Wandstärkenverteilung. Die Kugeln werden über Verfahren ähnlich der Herstellung von Emulsionen/multiplen Emulsionen im Materialsystem Polysiloxan-Tensid-äußere (wässrige) Phase hergestellt mit der Besonderheit, dass nach dem Emulsionsprozess die innere bzw. mittlere, aus einem präkeramischen Polymer bestehende Phase einen flüssig-fest-Übergang durchläuft. Die geometrischen Eigenschaften der Kugeln werden mit Hilfe von Tensiden und Tensidgemischen sowie mit Hilfe der äußeren Phase gesteuert. Die Einstellung der chemischen, mechanischen und thermischen Eigenschaften erfolgt über die Zugabe von Füllstoffen sowie über die Parameter der thermischen Umwandlung zur Keramik. Es werden Zusammenhänge abgeleitet, mit deren Hilfe der Prozess der geometrischen Strukturbildung beschrieben und auf weitere Systeme übertragen werden kann.

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Ziel des Vorhabens ist die Herstellung von thermoschockbeständigen Feuerfest-Keramiken auf der Basis des zweiphasigen Systems Alumiuniumoxid/Mullit über sol-gel-Prozesse mit partikulär gefüllten Solen. Dabei dient das Sol-System auf Basis niedrigmolekularer SiO2-Vorläuferstufen während der Formgebung über Gießprozesse als Matrix- und Transportmedium für Aluminiumoxid-Partikel und nach dem flüssig-fest-Übergang während der thermischen Behandlung als SiO2-Quelle für die in-situ-Bildung der Zweit-(Matrix-)phase Mullit. Die Bildung von Mullit erfolgt dabei an der Grenzfläche zwischen der Matrix und der Al2O3-Partikelphase, resultierend in einer Kern-Schale-Struktur mit verbesserten thermomechanischen Eigenschaften. Der Anteil beider Phasen wird über die Zusammensetzung des Gießschlickers und die Parameter der thermischen Umwandlung im Temperaturbereich zwischen 1200 °C und 1500 °C gesteuert. Die Ergebnisse der Mikrostruktur- und Festkörpercharakterisierung werden mit den Ergebnissen der Hochtemperatur- und Thermoschockuntersuchungen korreliert und Struktur-Eigenschaftsbeziehungen aufgezeigt, mit deren Hilfe die Werkstoffeigen­schaften gezielt eingestellt werden können.

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Keramische Schäume, insbesondere solche mit hierarchisch aufgebauter Porenstruktur gewinnen zunehmend für ingenieurtechnische Anwendungen wie Sorption, Katalyse, Gastrennung und Wärmespeicherung/Wärmetransformation an Bedeutung. Dabei begünstigen makroskopische Schaumzellen den fluiden Stofftransport, während Meso- und Mikroporen die katalytische oder Sorptionsfunktionalität darstellen bzw. durch Aufnahme von Gastkomponenten eine weitere Möglichkeiten zur Funktionalisierung bieten. Die Ziele dieser Arbeiten sind folglich:  i) zellulare keramische Monolithe mit definierten Porosität im Mikrometerbereich zu versehen,ii) Erkenntnisse zur Bildung dieses Funktionsporentypus zu erlangen sowie iii) Korrelationen zwischen bimodaler Porosität und mechanischen Werkstoffeigenschaften aufzuzeigen.  Im Rahmen des Projekts werden polymerabgeleitete Keramikschäume nach bekannten Verfahren hergestellt und simultan durch Zusatz ausbrennbarer Platzhalter gezielt mit einer Stegporosität versehen. Die Charakterisierung erfolgt hinsichtlich der (makroskopischen) Zellmorphologie, der Porosität in den Stegen und der mechanischen Eigenschaften. Zur Charakterisierung werden Computertomographie, verschiedene Methoden der Elektronenmikroskopie und Methoden der Porositäts- und mechanischen Charakterisierung monolithischer Festkörper herangezogen. Mit den gewonnenen Erkenntnissen wird der Einfluss der Stegporosität auf die mechanischen Eigenschaften beschrieben.

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The growing concern over increasing energy cost and global warming associated with fossil fuel source has stimulated the search for cleaner, more sustainable energy sources. Among viable technologies, the thermoelectric (TE) material based devices have received much attention. The main advantages of the TE devices are solid state operation, zero emission, high scalability, no maintenance cost and long operating life. However, TE materials, though known for long time have been too inefficient to be cost effective in most of the applications. Hence to increase the efficiency, the electrical conductivity hast o be increased while maintaining the thermal conductivity to a minimum. One of the most promising candidates is SrTiO3 showing a very high ZTvalue, which is a measure for the efficiency of a TE genrator. Aim of this project ist o develop a processing route for coating of a substrate material with SrTiO3 and doped relativ materials. Within this work a strategy will be developed for future work and process improvement.

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Ziel des Vorhabens ist die Herstellung von keramischen, thermisch aktivierbaren Funktions­schichten auf Stahl, Kupfer und Titanlegierungen auf Basis sauerstofffreier Polysilazane und sauerstoffhaltiger Polysiloxane über einfache Beschichtungsverfahren. Über Zusammensetzung des Beschichtungssystems, Prozessparameter der Polymer-zu-Keramik-Umwandlung und Pyrolyseatmosphäre können die Eigenschaften der zu generierenden Schichten gezielt eingestellt werden. Im Rahmen dieses Projekts wird untersucht, inwieweit die die geometrische Struktur von Füllstoffpartikeln genutzt werden kann, um diese auf den Schichten abzubilden. Auf diese Weise sollen mikro- und nanostrukturierte Oberflächen geschaffen werden, die einen erweiterten Funktionsumfang aufweisen.

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Das Projekt befaßt sich mit der Herstellung und Charakterisierung hochpermeabler ferromagnetischer Schichten mit einstellbarer Anisotropie und Magnetostriktion, wie sie beispielsweise in GMR-Sensoren Anwendung finden.

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