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This article gives an overview about the preparation and characterization of asymmetric ceramic membranes that have been developed at our institute within the last years. Depending on the required pore size of the filter active layer for filtration applications ranging from microfiltration (MF) up to nanofiltration (NF) different preparation routes have to be applied.

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Nanocrystalline zirconium dioxide particles have been produced by means of thermal decomposition of a liquid metal organic precursor in a flow reactor system. X-Ray diffraction patterns show that the powder consists of a mixture of the monoclinic and tetragonal phase and that the phase fractions depend on the experimental conditions during the preparation as well as on the subsequent thermal treatment of the sample. The mean particle diameter of the synthesized powders is ca. 40-50 A ˚as estimated from the line width of Bragg reflections and from transmission electron micrographs. The crystallites are non-porous and exhibit a rough surface incorporating a high concentration of low-coordinated surface sites. In agreement with the small particle size, the powder has a high specific surface area (>200 m2 g−1), which surmounts that of commercially available materials by a factor >3. The structure and morphology of the particles is essentially preserved during extensive thermal treatment up to 500 °C. Hydroxyl groups as IR active surface probes clearly indicate that the phase fractions on the surface and in the bulk strongly differ from each other.Low-coordinated OH groups on monoclinic surface domains give rise to H/D exchange reactions with D 2 already at room temperature. They are evidenced and monitored with time by FTIR spectroscopy.