Preparation of hollow fiber membranes from mullite particles with aid of sintering additives

Porous mullite hollow fiber membranes were prepared with a combined phase-inversion and sintering method, using three sintering additives including yttrium stabilized zirconia (YSZ), small mullite particles (SMP), and titanium oxide (TiO₂) to promote the particle sintering. The results indicated that all the three additives could improve the sintering performance of mullite hollow fiber membranes due to the decrease in activation energy of mullite grains. Both YSZ and TiO₂ could react with mullite grains to generate composite oxides (e.g., ZrSiO₄ and Al₂TiO₅) during sintering, following a reaction-sintering mechanism. Interestingly, the newly generated ZrSiO₄ was instable and further decomposed into monoclinic ZrO₂ and SiO₂ in the sintering process. The decomposition could avoid excessive embedment of composite oxides among mullite grains which have negative impact on mechanical strength of mullite hollow fibers. Overall, the doping of YSZ provided a better promotion effect on the sintering of mullite hollow fiber membranes, where the microstructural and mechanical properties are insensitive to the doping content and sintering temperatures, so it could be used as the candidate for the large-scale preparation of mullite hollow fibers.