Molecular separations can be achieved with minimum energy requirements when employing selective membranes. Inorganic membranes exhibit desirable properties, such as chemical inertness, high strength and permeable, in aggressive environments. The opti-mization and characterization of layered, asymmetric inorganic membranes is detailed in this text.
Defect free membrane supports are prepared by vacuum driven filtration of aqueous pH 2.0 HNO3 stabilized suspensions of AKP30 α-Al2O3 powder. The permeability and strength of the supports was found to improve while preserving sufficiently low surface roughness by targeting coarsening of the microstructure, driven by surface migration, during sintering.
Highly permeable membrane carriers/supports are prepared from coarse α-Al2O3 particles (>1 µm) by familiar colloidal approaches with weakly stabilized suspensions. The cost price of the carriers is decreased and sufficient strength achieved with low temperature phosphate bonding. Allowing the weakly stabilized and unhindered suspensions to settle prior to vacuum filtration allows for generation of a microstructure that is graded with respect to particle size. The carrier is highly permeable and has excellent surface morphology for subsequent deposition of thin films.
Site-specific milling of electron transparent foils with a focused ion beam and the subsequent analysis of those foils by TEM reveal incorporated agglomerates and interfacial cracking in state-of-the-art γ-alumina membranes. Purification of the Boehmite precursor sols to break down and remove agglomerates results in a uniform particle size distribution, which results in a much improved membrane homogeneity and adhesion. γ-Alumina’s improved microstructure aids in enhanced water purification.
Permeation porometry (PP) is used to investigate the connective pore-size distribution of asymmetric meso-porous membranes. PP has been proposed as a means to detect the occurrence of membrane pinholes; however, it is found that artifacts in the desorption isotherm are misinterpreted as pinholes. The artifacts are caused by a combination of chemical diffusion though the cyclohexane pore-blocking liquid in the membrane, and gradual removal of cyclohexane from the support.
The development of textured indium-tin oxide thin films is used to demonstrate how techniques such as rapid thermal processing can be implemented to decrease the cycle time and improve the homogeneity of thin film inorganic membranes prepared by wet chemical methods.