Development of Asymmeteric Membranes for Oxygen Separation by Tape Casting and Dip Coating
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Ceramic membranes made from mixed ionic and electronic conductive oxide materials have received much attention over the last decade due to their ability to separate oxygen from air at 100 % selectivity. The flux through these mem- branes may be optimized by reducing their thickness. A porous support of the same composition is applied to ensure sufficient mechanical stability. The pro- cessing of these so-called asymmetric membranes is addressed in this work; for the technology to become attractive from a commercial point of view, a reliable and cost-effective processing procedure needs to be established.Phase pure La0.2Sr0.8Fe0.8Ta0.2O3−δ (LSFTa) and La0.2Sr0.8Fe0.8Al0.2O3−δ (LSFAl) powders were synthesized by solid state reaction. The powders were used to prepare porous supports by the means of aqueous based tape casting and hot-press lamination. The supports were pre-sintered at various temperatures and dip coated with an ethanol-based suspension containing sub-micrometer sized spray pyrolysis powder. Different parameters believed to affect dense layer for- mation by dip coating are discussed and related to the experimental observations. It was found that an important criteria for success is to have a similar shrinkage property in the functional and porous layer of the membrane. The most promis- ing asymmetric membrane was obtained for the LSFTa composition where dip coating two times and sintering at 1230◦C resulted in a 6?7 μm thick membrane layer and a support with 38 % open porosity.The fracture strength of LSFAl supports with ∼ 64 % porosity was also charac- terized in this work. Testing 11 specimens with the ball-on-ring method resulted in a characteristic strength of 10.7±0.5 MPa and a Weibull modulus of 5.9±1.8.