Manufacture and filtration performance of glass filters made from capillary suspensions

Abstract

This research highlights the potential of capillary suspensions in tailoring the properties of glass filters and improving filtration performance. Borosilicate glass 3.3 filters fabricated in a wet processing route based on capillary suspensions were developed. Their filter properties and filtration performance as well as control of shrinkage and porosity gradients during sintering were investigated. The use of capillary suspensions significantly reduced green body shrinkage. Long residence times and spatially inhomogeneous heat transfer during sintering favored the formation of porosity gradients. Pore size, porosity, permeability and flexural strength of the filters could be tailored by adjusting capillary suspension composition and sintering conditions. Glass filters with particularly high permeability and small pore sizes were successfully developed. Filtration experiments with Oenococcus oeni and polystyrene spheres (diameter ≈ 1 μm) were conducted, showing that filtration efficiency and flux depend on pore size and open porosity. Crack-free asymmetric glass membranes with improved filtration performance were developed. Compared to dry processed commercial benchmark filters, the capillary suspension-based filters made from the same glass powder had higher pore sizes and permeability. At similar pore size and porosity, filters based on capillary suspensions showed significantly higher filtrate flux than the commercial benchmarks due to a more uniform pore structure.