New anisotropic ceramic membranes from chemically fixed dissipative structures

The formation of highly ordered capillaries in alginate gels is due to a dissipative convective process resulting from opposing diffusion gradients and friction. Ceramic membranes with an anisotropic pore structure have been gained from this self-organization process by incorporating inorganic particles into the gel matrix, followed by subsequent ion exchange, drying, and sintering. The aim of this study was to overcome existing preparative deficiencies and to optimize the capillary structure and surface properties with respect to specific technical applications. A new method of ion exchange was introduced, and the sintering program was improved to obtain reproducible product quality. By controlling the parameters of the self-organization reaction, the overall porosity of the ceramic membranes was adjusted to selected values between 60% and 83%. Capillary sizes were varied between 8 and 50 Am. Further modification by metal plating, particle coating, or hydrophobization led to an extended spectrum of applicability of the ceramic membranes. For the first time, anisotropic capillary ceramics have been characterized in detail as to their technical use as catalyst supports, filter membranes, or other solid-fluid and solid-gas contact processes.