Tailoring asymmetric Al2O3 membranes by combining tape casting and phase inversion

This study aimed to combine the techniques of tape casting and phase inversion to produce highly permeable ceramic membranes suitable for microfiltration in a single sintering step. The morphological, mechanical and textural characterization was performed using SEM, flexural strength measurement, mercury porosimetry and X-ray micro-computed tomography. Alumina membranes were produced using different slurry formulations and solidified via phase inversion, followed by sintering at 1400 or 1500 °C. Additionally, a co-casting strategy was successfully used for some membranes aiming to reduce the flux resistance caused by the dense layer usually formed at the bottom of ceramic membranes produced by phase inversion while the thin skin layer is preserved. Ceramic membranes with large pore sizes of the skin layer (0.30–0.42 μm) and high total porosity (46–75%) were obtained, and a clear increase of the mechanical resistance is observed when increasing alumina loading. Pure water flux of 52.4 and 26.60 m3 m-2 h-1 at 1 bar, and 27.60 and 41.11 MPa maximum flexural strength were achieved for membranes produced from slurries containing 45 and 50 wt% alumina, respectively. Simulations of permeability carried out from X-ray micro-computed tomography images in three axes proved a preferential fluid flow in the z-axis (from top to bottom) for different membrane regions and demonstrated that permeability is mainly influenced by the top skin and bottom layer morphology, which is in agreement with the experimental results.