## 3 Results and Discussion  
The general temperature used in the sintering process to fabricate the ceramic hollow fiber membrane is about 1300 to 1500 \({}^{\circ}\)C, therefore the sintering temperatures of 1400 and 1500 \({}^{\circ}\)C are investigated in this study. SEM analysis confirmed the morphologies of the as-sintered alumina hollow fiber membrane sintered at 1400 and 1500 \({}^{\circ}\)C. As shown in Figure 2a,b, the alumina grain size of the outer surface sintered at 1400 \({}^{\circ}\)C is slightly smaller than that at 1500 \({}^{\circ}\)C, and for both the outer surface consists of visible alumina grains and a preliminary result for the pore size of several hundred micrometer are evident. From the cross-sectional SEM images (Figure 2c,d) of the as-sintered alumina hollow fiber membrane, it is seen that a symmetrical fiber with an inner and outer diameter of 0.8 and 1.2 mm for 1400 \({}^{\circ}\)C sintering and that of 0.8 and 1.3 mm for 1500 \({}^{\circ}\)C sintering are produced. Figure 2e,f both show the typical microstructure that results from the phase-inversion method. For both fabrications sintered at 1400 and 1500 \({}^{\circ}\)C, a finger-like structure extends from two surfaces and a sponge like structure fills the middle part, which shows that the spinning procedure is successful. The finger-like structure, which occupies at least 70% of the entire structure, observed in Figure 2e, is slightly more than that observed in Figure 2f, and the more finger-like structure may result in a better permeating characteristic. Figure 2: The morphologies of the as-sintered alumina hollow membrane sintered at different temperatures: outer surface sintered at **(a)** 1400 \({}^{\circ}\)C and **(b)** 1500 \({}^{\circ}\)C; cross-sectional sintered at **(c)** 1400 \({}^{\circ}\)C and **(d)** 1500 \({}^{\circ}\)C; partial cross-sectional sintered at **(e)** 1400 \({}^{\circ}\)C and **(f)** 1500 \({}^{\circ}\)C.  
The mercury porosimeter results for the as-prepared fiber are shown in Figure 3. It is seen that both of the pore size measurements are in the range of 100 to 400 nm, that give average pore size of about 220 and 165 nm for 1400 and 1500 \({}^{\circ}\)C sintering, respectively. They both are consistent with the appropriate pore size of 0.1 to 1 \(\upmu\)m that has been reported for MD. In addition, the porosities of 55% and 33% were measured for the materials sintered at 1400 and 1500 \({}^{\circ}\)C, respectively. The as-sintered hollow fiber is intrinsically hydrophilic because of the presence of hydroxyl groups on the fiber. In order to use the fiber for MD, FAS, which is a general agent for hydrophobization, was used to hydrophobilize the fiber by the method mentioned previously. A pure water permeation test was carried out before and after hydrophobization, to determine the permeability and the LEP\({}_{\mathrm{w}}\) value which determines the applicability for MD. The results of the pure water permeation as a function of the pressure difference between the feed and permeate sides are shown in Figure 4. The pure water fluxes of the fiber sintered at 1400 and 1500 \({}^{\circ}\)C both increase almost linearly with pressure difference before hydrophobization, and pure water fluxes of about 3000 and 2600 \(\mathrm{Lm^{-2}h^{-1}bar^{-1}}\) are recorded. The higher pure water flux of 3000 \(\mathrm{Lm^{-2}h^{-1}bar^{-1}}\) is attributed to the larger average pore size (220 nm) and the higher porosity (55%) mentioned above. However, the water flux could not be detected after hydrophobization until a specific pressure difference, which means the LEP\({}_{\mathrm{w}}\) value. The LEP\({}_{\mathrm{w}}\) value of 2.5 bar for 1400 \({}^{\circ}\)C sintering (Figure 4c) is lower than that of 4.5 bar for 1500 \({}^{\circ}\)C sintering (Figure 4d), and this result is in accordance with the larger average pore size of 220 nm. Both LEP\({}_{\mathrm{w}}\) values are higher than the pressure difference of about 1.0 bar used in VMD, which also demonstrates the applicability.