Papers by Author: Herwig Peterlik

Abstract: Micro-and mesoporous ceramics demonstrate promising properties for applications in energy-and environment-related fields. Due to their high thermal and chemical stability, they are particularly suited for separation in harsh thermal or chemical environments, e.g. as membrane materials for the separation of gas mixtures. In this work, we present the use of a preceramic poly(vinyl)silazane in combination with organic molecular porogens for the generation of micro-/mesoporous non-oxide ceramic structures. Microporosity is generated during the pyrolytic conversion process, while the addition of molecular porogens, to be removed during the heat-treatment, enables further control of the micro-/mesopore structure. A systematic investigation of various porogens showed the suitability of polystyrene for this purpose. Based on these findings, the pore structure and pore connectivity of polysilazane/polystyrene-derived structures were evaluated using gas physisorption and small angle X-ray scattering techniques. This material was further investigated by preparing asymmetric membranes consisting of micro-/mesoporous polysilazane/polystyrene-derived layers on porous ZrO₂/TiO₂ supports. The potential for gas separation applications was then demonstrated by single-gas permance evaluation of the generated structures at temperatures up to 300 °C.

Abstract: A novel procedure, based on the Resonant Beam Technique, and its application to anisotropic composites is presented. The evaluation of the elastic modules of anisotropic materials from the measurement of the transverse eigenfrequency spectra of resonant beams is performed by a two step process: firstly the beams cut out from the test material in different directions are evaluated in-dependently of each other under the assumption, that they are isotropic, solving Timoshenko´s equations using an isotropic correction factor for shear. Secondly the beams are evaluated together as representatives of one anisotropic material, using an anisotropic correction factor for shear. The equipment, developed for such measurements is presented. Finally, the procedure is applied to a transversely isotropic carbon fibre-reinforced carbon composite and the relevance of the results is discussed.

Abstract: Creep tests have been performed for carbon fibre bundles (Toray, HTA5131) in a temperature range from 1500 °C to 1800 °C and at various stress levels in a tensile testing machine in vacuum (pressure was kept below 10-3 mbar). Creep parameters have been obtained from the diagrams elongation versus time. X-rays (SAXS and WAXD) have been used for accompanying structural investigations. An increase in the alignment of the graphene sheets with respect to the fibre (and thus the loading) axis was observed with increasing test temperature. For fibres stabilised by heat treatment (2 hours, 2100 °C, without load) no creep and no structural change could be observed.