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.

A new direct foaming method to produce macroporous cellular ceramics using surfactants as foam stabilizers is presented. The technology relies on the transition of a stabilized aqueous ceramic powder suspension containing a homogeneously dispersed alkane or air–alkane phase into cellular ceramics. The stabilization of the powder suspension and the emulsion is realized with particular emphasis on the interaction of both mechanisms providing enduring stability of the system up to high foaming degrees. Anionic, cationic, and nonionic surfactants were studied with their stabilization and foaming effects. The presence and influence of air bubbles was proved to be of negligible importance. Foaming is then provided by the evaporation of the emulsified alkane droplets, leading to the expansion of the emerging foam and giving rise to solids foams with cell sizes from 0.5 to 3 mm and porosities up to 97.5% after sintering. The microstructures of these filigree ceramics are stable and rigid with dense struts and uniform distributions of the solid phase and the porosity.

No abstract

No abstract

No abstract

No abstract

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.

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.