The development of ceramic hollow-fibre membranes has gradually grown in the past
decade. This specific geometry which has a high surface area per unit volume can
dramatically increase the efficiency of separation processes and can be adapted to a
variety of industrial applications. In addition, ceramic membranes are well known for
their superior chemical and thermal stability which allows them to operate at high
temperatures and/or in chemically harsh environments. Nevertheless, the main
challenge for their industrial application is their insufficient mechanical strength.
Yttria-stabilized zirconia (YSZ) is selected as a membrane material in this study. This
is because the material has superior mechanical strength and it is relatively cheaper
than other ceramic materials. The ionic conducting property of YSZ material is also a
benefit when it is used in electrochemical applications.
Porous and dense YSZ hollow-fibre membranes have been developed in the study
using a combined phase inversion and sintering process. Different membrane
morphologies, surface properties, mechanical strength and porosity could be achieved
by controlling the YSZ content and sintering temperature. The developed YSZ
hollow-fibre membranes with porous or dense structures show great potential for a
variety of applications.
Porous YSZ hollow-fibre membranes can be used as membrane contactors in aqueous
media or for fluid separations in harsh environments, which most polymeric
membranes cannot withstand. For the application of membrane contactors in aqueous
media, the nature of the YSZ membranes must be modified from hydrophilic to
hydrophobic in order to keep them non-wetted during the aqueous contacting
A robust and hydrophobic YSZ hollow-fibre membrane was developed by introducing
a pretreatment technique, followed by a grafting procedure. The hydrophobic YSZ
membrane was found to be thermally stable up to 270 °C and chemically stable in
hexane for 100 h. This membrane was then applied to the absorption of carbon
dioxide from a high concentration aqueous ethanolamine solution. The results demonstrated the high efficiency of the ceramic hollow-fibre membrane contactor
compared to traditional devices.
Dense YSZ hollow-fibre membranes with outer diameters of 1.28 mm have been used
as an electrolyte support in a solid oxide fuel cell. The YSZ electrolyte-supported
SOFC was prepared at relatively lower sintering temperatures and shorter sintering
durations. The YSZ-based hollow fibre SOFC demonstrated its ionic stability in a
redox environment and mechanical stability at temperatures up to 800 °C. The results
also demonstrated its electrochemical performance at high temperature.
In summary, this thesis focuses on the development of YSZ hollow-fibre membranes
from the initial step of fabricating the membrane to the final step of their potential
application. Different structures of YSZ hollow-fibre membranes were studied,
discussed and their potential performance was compared to the achievements of
others in order to gain more understanding and information on the use of the
membranes for practical applications.|