Filtration Performance of Membranes Produced Using Nanoscale Alumina Fibers (NAF)

This paper outlines a procedure for producing membrane materials, using a novel alumina fiber with a diameter of the order of 10 nm and a range of processing conditions. The as‐received fibers had very high aspect ratios and were supplied in the form of mats in which they were unidirectionally aligned. Membranes have been produced by dispersing the fibers in a liquid, together with a binding agent, followed by sedimentation. During dispersion, the fibers tended to break up and become detached from each other. Depending on the period of dispersion, the fiber architecture in the membranes could range from a “duplex” structure containing bundles of locally aligned fibers to a more homogeneous assembly of relatively short fibers. Some samples exhibited a stratified structure, with a homogeneous layer below and a duplex structure above. Correlations have been established between these architectures and transport properties relevant to use of these membranes as fine scale filters. Measurements have been made of the specific permeability, using water as the permeating fluid. The results are consistent with predictions based on the Carmen–Kozeny equation. The filtration efficiencies of the membranes have also been assessed, using two dyes with different molecular weights. This performance was found to be consistent with filtration taking place primarily by simple mechanical entrapment of the dye molecules. Relevant mechanical properties of the membranes have also been measured, notably the stiffness (Young's modulus) and the tensile strength. These results are briefly considered in terms of implications for the durability of the membranes as filters. It is concluded that these membranes, perhaps particularly those with duplex or layered structures, offer considerable promise as ultra‐fine scale filters.