title: Hierarchy in inorganic membranes.
abstract: Thin films of a few μm thickness for particle filtration and gas separation cannot be applied as self-supporting layers since they are mechanically insufficiently strong. Therefore, these top layers for particle filtration and gas separation are usually deposited on porous mechanically strong supports with a hierarchical pore structure. To reduce the pressure drop of a gas stream over the membrane and to ensure high fluxes in filtration and gas separation, the cross section of the support is usually asymmetric or graded with a small thickness of the layer with the smallest pore size called the top layer. Since the pressure drop over a capillary with radius r is ∼r(4), the layer with the smallest pore size should be as thin as possible. The disk-like planar supports are usually prepared by sequential tape casting which is an expensive technology. Tubular supports with a hierarchical cross section can be prepared in one step by hollow fiber spinning, double mantle spinning or centrifugal casting.
authors.affiliation: Institute of Physical Chemistry and Electrochemistry, Leibniz University Hannover, Callinstr. 3A, 30165 Hannover, Germany. juergen.caro@pci.uni-hannover.de.
authors.forename: Juergen
authors.initials: J
authors.lastname: Caro