A New Approach to Design High Porosity Silicon Carbide Substrates

Diesel particulate filters (DPF) are now a mandatory part in diesel exhaust aftertreatment systems in order to achieve compliance with current emission legislations. However future demands for further NOx and CO₂ reductions combined with a maximum amount of allowed particle numbers per ccm lead to special requirements for the DPF substrate material. On the one hand high filtration efficiency of soot particles in the nanometer scale has to be reached and on the other hand high porosities and large pore sizes have to be realized to support catalytic coating. In order to have a base material composition which can easily be modified to meet current and future demands a new SiC substrate, called XP-SiC, was developed. The technology of the XP-SiC is based on a reaction forming process of coextruded silicon and carbon particles to SiC. This new manufacturing process leads to a unique microstructure with a sponge-like appearance and a high porosity in the range of 50% - 70%. Key properties are its high filtration efficiency and low bulk weight at low back pressure and high soot mass limit.

The aim of this paper is to give an introduction to this new material. As examples we will show, that, depending on heat treatment it is possible to create membrane-like structures to achieve high filtration efficiency in both new and fully regenerated state, as well as open surface structures for applications with focus on low back pressure and high wash coat loadings.