Platinum induced crosslinking of polycarbosilanes for the formation of highly porous CeO2/silicon oxycarbide catalysts

A new synthesis scheme for the formation of porous CeO2/Pt-polycarbosilane composites using inverse microemulsions is presented. Aqueous hexachloroplatinic acid was used as a hydrosilylation catalyst causing crosslinking of allyl groups in a liquid polycarbosilane (PCS). The resulting polymers are temperature stable and highly porous. The Pt catalyst content and post-treatment of the polymer can be used to adjust the porosity. For the first time hydrophobic polymers with specific surface areas up to 896 m(2)/g were obtained by catalytic crosslinking of polycarbosilanes. Ceria nanoparticles 2-3 nm in diameter are well dispersed in the PCS matrix as proven using high resolution electron microscopy. Porosity of the hydrophobic materials could be increased up to 992 m(2)/g by adding divinylbenzene in the oil phase. Pyrolyses at 1200-1500 degrees C and post-oxidative treatment at various temperatures produce porous ceramic structures with surface areas up to 423 m(2)/g. X-Ray diffration investigations show that the crystallinity of the SiC matrix can be controlled by the pyrolysis temperature. Post-oxidative treatments cause silicon oxycarbide formation. Structure and morphology of the polymeric and ceramic composites were investigated using Si-29 MAS NMR, FESEM, FT-IR and EDX techniques. The temperature programmed oxidation (TPO) of methane shows a high catalytic activity of CeO2/Pt-SiC(O) composites lowering the onset in the TPO to 400-500 degrees C

Biomimetisch geprägte Hochleistungskeramiken für den Anlagenbau (BioCerAb): Abschlussbericht zum BMBF-Forschungsvorhaben

It was the overall aim of the compound project "Biomimetisch geprägte Hochleistungskeramiken für den An lagenbau" (BioCerAb), to prove, that biomimetically derived high efficiency ceramics for mechanical engineering and construction are feasible and also applicable. Within the course of the project it could be shown, that bionical pre-products for the manufacturing of ceramic components opennew perspectives in the field of ceramic technologies. As bionically derived pre-products, budget-friendly wood fibre boards could be used, which were converted into carbon through pyrofysis and consequently by reaction silicon treatment into ceramic SiSiC-components. One intrinsic aim of the entire project was, to display the entire production chain and to come to reach a cost efficient, lean production process, with which these newly developed ways of producing ceramic components was economically feasib le, ft was especially about producing big sized complex ceramic components for technical applications. The biogenic base material was planned to possibly convert the hierarchically organized biological structure through capillary silicon treatment into the desired clear cut microstructure of SiSiC-ceramics. In order to give proof of the feasibility of biomimetically derived high efficient ceramics for mechanical engineering and construction, two demonstration components were chosen: demonstrator component 1 was a complex, ceramic heat-exchanger, whereas demonstrator component 2 was a big-sized, ceramic wear protection from the field of pump construction. The two systems were chosen, because they form typical examples for the favourable use of ceramic materials in mechanical engineering and construction and which were as yet not disposable by means of conservative technology because of economic reasons and restricted possibilities of production. The two components in question were designed to show the broad variety of material and the technical applicability of biogenic ceramic material und the big-sized products manufactured from them, especially in the field of mechanical engineering and construction as well as plant engineering. It also gives a first insight into the new production technologies for these fields of application