Structural characterization of asymmetric yttria stabilized zirconia hollow fibre membrance

Abstract

Ceramic membrane is proven to overcome a limitation of using polymeric membrane for applications that requires a high temperature and pressure. In this study, Yttria-stabilized zirconia (YSZ) was selected as a ceramic material due to its superior mechanical strength. YSZ hollow fibre membrane was fabricated using combined dry-wet phase inversion and sintering technique. Four parameters involved during fabrication process have been varied systematically to study the effect on YSZ hollow fibre membrane structure and properties. The ceramic loading was varied from 55 wt.% to 67 wt.% and the YSZ/polyethersulfone (PESf) ratio was varied from 7 to 10 during YSZ suspension preparations. Then, the air-gap length was varied from 15 cm to 30 cm during spinning process. Lastly, the sintering temperature was varied from 1250 oC to 1400 oC during sintering step. The YSZ hollow fibre membrane produced were characterized in terms of morphology, mechanical strength, apparent porosity, pure water flux and solute rejection. The results successfully showed an asymmetric YSZ hollow fibre membranes consist of finger-like voids and sponge-like voids were produced. The YSZ suspension viscosity was increased with the increase of YSZ loading and decrease of YSZ/PESf ratio. High suspension viscosity favored the growth of finger-like voids and limited the formation of sponge-like region across the membrane. This result was similar to increase of the air-gap length during spinning. Significant densification occurred at the sponge-like region during sintering. The formation of isolated voids at 1400 oC hindered the pure water permeation. However, the mechanical strength increased with the sintering temperature. From the permeation test, the YSZ hollow fiber membrane prepared with 65 wt.% loading, ceramic/polymer ratio of 10, spinning at 20 cm air-gap length and sintered at 1300 oC was the most preferable membrane. This membrane had a pure water flux of 118.4 Lm-².hr-¹ with a molecular weight cut off of 50 - 60 kDa and mechanical strength of 224 MPa.