Fabrication of highly porous glass filters using capillary suspension processing

We present a novel, capillary suspension based processing route for sintered glass filters with porosities >= 50% at average pore sizes between 1 and 50 mu m. This new kind of glass filters exhibits narrow pore size distribution and uniform pore structure. Pores are exceptionally smooth and round. Accordingly, permeability and mechanical strength of these filters excel that of similarly processed ceramic and commercial glass filters significantly. Mechanical strength at a given porosity is much higher than that of commercial glass filters and reaches values similar to that of ceramic filters with distinctly higher matrix strength. Absolute values are well predicted by the Gibson & Ashby model sigma(c)/sigma(f,0) = B-0 (1 - epsilon)(z) with B-0 = 0.8. Liquid permeability varies with pore size according to Darcy's law but absolute values are clearly higher than that for ceramic filters at given pore size as expected from the smoother pore structure. Gas permeability is especially high at pore sizes <10 mu m and exceeds that of ceramic and commercial glass filters significantly. Moreover, this results in a weaker than quadratic pore size dependence. This is presumably due to slip effects occurring especially in small pores and narrow necks of the novel glass filters. (C) 2015 Elsevier B.V. All rights reserved.