Twenty‐five years of diesel particulate filter (DPF) developments have shown that ceramic materials are well‐suited candidates to fulfill the harsh requirements of exhaust after treatment. The introduction of DPF in passenger cars in Europe in 2000 was a real breakthrough from both a scientific and a commercial point of view. Different systems and filter materials can be used as DPF; however, at the moment silicon carbide wall flow filters seem to be at advantage. There is a continual demand for cost‐effective and reliable materials and systems forced by increasing legal emission standards.

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Open cell foams made on the basis of reticulated polyurethane foams are well known and widely used since decades. Polyurethane foams have been commercially produced since the 1950 s. [1] They are a practically ideal porous organic structure with porosities between 97 and 98%. First attempts to transfer these structures into ceramic foams by a powder slurry replication technique have been described by Schwartzwalder in 1961, [2] and nowadays such foams are produced in the order of 160 million parts per year for the use as filter in the cast shop. The replication technique has been transferred into the manufacturing of metal foams for the first time in 1966 in order to use them as porous battery electrodes. [3] In the 1970 s, notable work has been done by Russian research groups, where metal foams made by replication method were mainly used in catalysis or filtration applications. [4] Over the past ten years the method has been reinvented by various groups. Mainly open cell foams on the basis of highly alloyed steels were produced, [5][6][7][8] but also foams on the basis of copper [9] or titanium alloys for the use as permanent biomedical implant [10] or low alloyed steel for degradable implants [11] were investigated. In the present work, open cell metal foams have been developed on the basis of various steels like SUS 316L, SUS 314, 4110, SUS 430L, FeCrAl, mild steels and non-ferrous metals like molybdenum, tantalum and the titanium alloy Ti6Al4V. The present paper shows the main properties and applications of replicated PU based metal foams. ExperimentalThe replication method essentially involves three production steps: First, a reticulated polyurethane sponge is coated by slurry impregnation. Reticulated polyurethane foam samples with cell sizes of 10, 30, 45, 60, and 80 pores per inch (Foampartner Reisgies, Germany) were coated using double rubber rollers. Water-based slurries with PVA-binder or carbon acid binder and solids content between 87 and 90% were used. In the next step, the template is thermally removed and finally the debinded metal structure is sintered.Thus, the open network of the polymer foam is transformed into a metal structure. The processing in principle is rather simple, but however, in order to obtain defect-free structures with optimum properties every single processing step needs for proper development. Firstly, in order to obtain complete impregnation of the PU foams fine metal powders High porosity permeable materials have been manufactured on the basis of the highly uniform structure of foamed polyurethane since the 1950 s. This paper shows the development of open cell foams based on all kinds of steels, titanium alloys, and also open-cell molybdenum foams made by a powder metallurgical replication technique. Such materials show a wide range of physical and mechanical properties, which may be adapted to various requirements. The automotive industry, for example, needs high-temperature resistant materials with high permeability and good strength for catalytic conversion. For orthopaed...

The structure and the electrical properties of porous and dense liquid-phase sintered silicon carbide ceramics (LPS-SiC), containing yttria and alumina additives, have been studied. The electrical resistance of LPS-SiC-materials varies in a wide range. This paper is focused on the influence of porosity on the electrical resistance of the sintered SiC. The porosity was controlled by the SiC grain size. Porous LPS-SiC materials were found to have substantially lower electrical resistance in comparison to dense materials of the same type. The structure of the materials was investigated by XRD and FESEM. The porous materials consist of large grains due to the coarser starting powders in comparison to the dense materials. This results in a reduction of the dissolved and re-precipitated fraction of the SiC during sintering. Using the in-lens SEM mode, the high conductivity of the formed rims of the SiC grains could be shown. These observations reveal that the rim volume of dense LPS-SiC is much more extended than the rims of porous materials showing the higher conductivity.

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