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Thanks to their high energy density and thermal conductivity, metallic Phase Change Materials (mPCM) have shown great potential to improve the performance of thermal energy storage systems. However, the commercial application of mPCM is still limited due to their corrosion behavior with conventional container materials. This work first addresses on a fundamental level, whether carbon-based composite ceramics are suitable for corrosion critical components in a thermal storage system. The compatibility between the mPCM AlSi12 and the Liquid Silicon Infiltration (LSI)-based carbon fiber reinforced silicon carbide (C/C-SiC) composite is then investigated via contact angle measurements, microstructure analysis, and mechanical testing after exposure. The results reveal that the C/C-SiC composite maintains its mechanical properties and microstructure after exposure in the strongly corrosive mPCM. Based on these results, efforts were made to design and manufacture a container out of C/C-SiC for the housing of mPCM in vehicle application. The stability of the component filled with mPCM was proven nondestructively via computer tomography (CT). Successful thermal input- and output as well as thermal storage ability were demonstrated using a system calorimeter under conditions similar to the application. The investigated C/C-SiC composite has significant application potential as a structural material for thermal energy storage systems with mPCM.

Because of the excellent fracture toughness and oxidation resistance, carbon short fiber reinforced ceramics have a sound potential for a variety of high-temperature applications. For the composite's reliable use in long-term applications, however, the oxidation effects on the mechanical strength are of crucial interest and have hitherto not been investigated in detail yet. In this study, the weight change of carbon short fiber reinforced C/SiC composites with carbon fiber lengths of 9 mm (long cut fiber composite – LCFC) and 2 mm (short milled fiber composite – SMFC), respectively, are evaluated in the temperature range from 500 to 1200 °C for two different fiber orientations. Both types of composites were additionally tested in bending mode after 25 and 50 min of exposure to air at 700 °C depending on fiber orientation. After 3 h of exposure at 1000 °C, a total weight loss of up to 37% for LCFC and 47% for SMFC could be determined. The bending test carried out after 50 min exposure at 700 °C showed a dramatic decrease down to 50% of the initial flexural strength for LCFC samples with fibers orientated in parallel to the beam axis. The smallest strength decrease of around 13% was found for SMFC samples with fibers orientated perpendicularly to the beam axis. Microstructural investigations suggest strongly that oxidation along the fibers is the most dominating weakening mechanism and is therefore directly affected by the fiber orientation and length.

In the present paper, the force-fit connection of discrete ceramic components by means of geometrically interlocking surfaces is studied. These surfaces possess a concavo-convex topology permitting assembly of structures in which each individual element is kinematically locked by its neighbors. Such structures have a tuneable bending stiffness, allow for large deformations and are tolerant to missing or destroyed elements. These properties of topologically interlocked structures make them particularly attractive in construction with brittle materials. The elements used were produced by freeze gelation of ceramic slurries, leading to near net shape with the coefficient of shrinkage below 3%. It is shown that planar assemblies of interlocked ceramic elements can withstand flexural deflections up to a ten-fold of those a solid plate from the same material can sustain. The response of these structures to concentrated load can be divided into an elastic and a quasi-plastic, i.e., irreversible, part. After the point of maximum load, the interlocked structures investigated were still able to withstand further deformation, whereas solid plates showed brittle failure.

Calcium phosphate ceramics have a high potential for biomedical applications. In this work Si-modified calcium phosphate ceramics were prepared from the silica-containing hydroxylapatite (HAp) suspensions using the freeze gelation technique, an environment-friendly low-cost method for the near-net-shape fabrication of ceramic components. Sintering behavior, phase composition, and microstructural characteristics of HAp with varying silica content were studied using dilatometry, thermogravimetry, XRD, REM, and Hg-intrusion. It was shown that the addition of silica has an essential effect on the sintering behavior and the phase composition of the samples and allows the in situ control over the HAp/Si–HAp to tricalcium phosphate (TCP)/Si–TCP ratio.

A new processing route for high-performance graded ceramic filters is presented. The direct foaming process is based on the transition of a surfactant-stabilized alkane dispersion in a stabilized aqueous ceramic powder suspension into mechanically stable ceramic foams with porosities up to 90%. The cell size distribution and, consequently, the permeability of the filters could be efficiently adjusted by the control of the high alkane phase-emulsified suspension (HAPES) microstructure during emulsification. Furthermore, open porous graded structures are produced by combining HAPES layers with different droplet sizes. The tailored microstructural features, providing controlled permeabilities as well as high compressive strength of the cellular ceramics are of special interest for applications where fluid transport through ceramic microstructures is required. These include filters, in particular for aerosol filtration, temperature control membranes in autothermal reforming, catalytic supports including supports for batteries as well as matrices for immobilized microorganisms.

Freeze casting is a fabrication method that allows producing near-net-shaped ceramics with variable porosity. Hydroxyapatite (HA) was modified by the addition of different amounts of SiO 2 nanoparticles during freeze cast preparation. The addition of SiO 2 introduced a partial phase transformation of HA to β-tricalcium phosphate and improved the form stability due to less shrinkage after sintering. The impact of surface roughness of pure HA ceramics and the influence of Si0 2 introduction during freeze casting on adhesion, proliferation, and differentiation of human osteoblast-like cells (MG-63) was investigated. While both cell attachment and proliferation of smooth pressed HA was significantly enhanced compared to rough freeze cast HA, the addition of SiO 2 improved the cell numbers of the latter. The expression of cell differentiation markers osteocalcin and collagen I was found to be supported by rough surfaces (R a = 5-6 μm) in particular on ceramics containing Si0 2 .

A new way to prepare magnesia-alumina-spinel was investigated making use of a mixed powder system of MgO and metallic Al-3 wt% Mg. Intensive ball milling was applied which provides the formation of new powder particles as composite of both components in intimate contact. The new configuration of the particles had a significant impact on the reaction sintering behavior leading to single phase spinel microstructures at moderate temperatures below 1400°C. Optimized milling of the powder mixture was therefore required providing reduced crystallite sizes and strongly enlarged interfacial area shared by the reacting components. The optimal milling time was identified by the complete reaction of the starting powders to spinel during sintering. Shorter milling times led to incomplete reactions and longer milling times contaminated the milling product by debris from the milling tools. The amount of interfaces generated by the intimate mixing dominated the sintering reaction kinetics whereas the specific surfaces area was of secondary importance.

Porous silicon oxycarbide (SiOC) ceramics in particular bulk and cellular structures are produced via polymer pyrolysis. By using optimal pyrolysis parameters (i.e., heating rate, maximum temperature) the addition of either solid fillers or chemically active additives is efficient in preventing the collapse of pore structure and controlling pore formation through decomposition. Fast pyrolysis can lead to crack formation and a loss of specific surface area at temperatures above 600°C, whereas slow pyrolysis is able to preserve mesopores up to 1200°C combined with high surface areas. These SiOC ceramics with bimodal pore size distribution are potential candidates for adsorption/separation processes under severe conditions.

Manufacturing ceramic powders and compacts by pyrolizing organosilicon polymers results in an amorphous microporous Si-O-C matrix with favorable high temperature strength and chemical stability compared to conventional porous organic matrices. Using this method the authors present the production of defect-free ceramics with ideally oriented channels.

Fur eine effektive Nutzung stoffwechselphysiologischer Eigenschaften von Mikroorganismen ist ihre Immobilisierung haufig von entscheidender Bedeutung. Die Entwicklung neuer, angepasster Immobilisierungssysteme aus bioorganisch-keramischen Hybridmaterialien (Biocere) stellt hier die Basis fur eine kontinuierliche Wasserstofferzeugung dar. Neben einer Immobilisierung in keramischer Matrix durch Gefriergelieren wurden Keramikschaume als Immobilisierungstrager eingesetzt. Das Gefriergelierverfahren erlaubt die Herstellung dimensionsstabiler Materialien variabler Zusammensetzung und steuerbarer Porositat bei gleichzeitiger Immobilisierung der Mikroorganismen in der entstehenden anorganischen Matrix. Durch gerichtetes Eiskristallwachstum wird eine kanalartige Struktur im Biocer gebildet. Die Verfestigung dieser attraktiven Porenstruktur durch den gefrierinduzierten Sol-Gel-Ubergang, die biokompatiblen Herstellbedingungen, die chemische Bestandigkeit und die Moglichkeit des Trocknens stellen die Ausgangsbedingungen fur einen entscheidenden technischen Fortschritt dar. Die erzeugten Kanalstrukturen ermoglichen im Betrieb eine kontinuierliche Abfuhr des in der Struktur erzeugten Gases. Wahrend freie Zellen nach erneuter Nahrstoffzugabe deutlich weniger Wasserstoff erzeugen, zeigen die immobilisierten immer wieder gleich hohe Werte. Die gewunschte Stabilisierung des Stoffwechsels der Zellen wird erreicht. Batch-Versuche zeigen, dass stark wechselnde Nahrstoffkonzentrationen sowie Nahrstoffmangel wahrend des Betriebs tolerabel sind. Durch Einleitung von Sporenbildung im Biocer lasst sich der Betrieb des Reaktors beenden. Die getesteten Biocere konnten nach einer Lagerung von einem Monat problemlos erneut aktiviert werden, bei gleich bleibender Aktivitat. Damit ist eine elementare Voraussetzung fur den realen technischen Betrieb gegeben: Abschaltbarkeit, Reaktivierbarkeit, beliebige Lagerfahigkeit.