Entwicklung von geträgerten protonenleitenden Dünnschichtmembranen für die Wasserstoffabtrennung

Hydrogen separation membranes offer a promising possibility to separate pure hydrogen from gas mixtures. Ceramic membranes from La$_{6-x}$WO$_{12-\delta}$ (LWO) are suitable for this application, because the separation in membrane reactors can take place at temperatures of more than 900 °C. LWO membranes are thermochemical stable under the existent operation conditions. To reduce the transport resistance, the membrane thickness has to be reduced, but that leads to a decrease of the mechanical stability. The solution for this is an asymmetric membrane architecture consisting of a thin dense membrane layer and a porous substrate. Though, a possible drawback is bending of the two-layered structures during sintering. The first part of this thesis deals with the synthesis and pre-treatment of the ceramic powders, as well as with the manufacturing of single membrane and substrate layers from LWO. The single layers are analysed regarding their sintering behaviour. Based on these findings, asymmetric two-layer systems consisting of membrane and substrate (thicknesses of 20 and 200 $\mu$m) are produced by the sequential tape casting. A detailed analysis of the sintering behaviour, the microstructure, and a comparison between single layers and two-layer assemblages is performed. Thereupon, further successful developments of the temperature programme and the substrate thickness are made. The bending of the two-layered system is eliminated as far as possible by these procedures. Another part of the thesis deals with magnesium oxide (MgO) as an alternative substrate material, because of its economic advantages over the manufacturing from LWO. For this purpose, single layers and two-layer assemblages with a MgO substrate are analysed regarding their chemical stability, their sintering behaviour, and their microstructure. It is shown that in future MgO can be used as a cheap substrate material. For an increase of the hydrogen flux the membrane material is modified by the substitution of tungsten by Mo and Re. Two-layer assemblages consisting of substituted membranes and different substrates from LWO and MgO are investigated concerning the formation of undesired secondary phases. Solely the combination of a Mo-substituted LWO membrane with a LWO substrate is suitable for further use. All other combinations cannot be manufactured defect free. To prevent the membranes from damage by chemical reaction with the substrate, intermediate layers have to be integrated as diffusion barrier when using MgO substrates. Finally, a hydrogen permeation measurement executed with a two-layer assemblage from pure LWO, is presented. The hydrogen flux is around 0.1 ml min$^{-1}$ cm$^{-2}$ at 775°C, which means an increase by a factor of 4 compared to bulk membranes