Development of Asymmeteric Membranes for Oxygen Separation by Tape Casting and Dip Coating

Abstract

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.