Fabrication of Low Cost Alumina Tube through Agar Gelcasting for Membrane Microfiltration

Tubular Al_2O_3 membranes for microfiltration were successfully fabricated by combined steps of agar gelcasting and then acetone-assisted drying. Firstly, Al_2O_3 slurry and agar solution were separately prepared prior to being mixed together at a constant temperature of 70°C. Subsequently, the warm mixtures were poured into assembled glass mold and then rapidly transformed into gel with tubular shape. The as-gelled tubes were demolded and then soaked in acetone for 50 h allowing rapidly drying of the gel tubes after removal from acetone due to a lot of evaporation of acetone in air atmosphere at room temperature. The tubular Al_2O_3 membranes were prepared from Al_2O_3 powder with the significantly different particle sizes of ~5 μm and 0.167 μm at different proportions of 0.167 μm Al_2O_3 powder from 5 to 20 wt%. The tubular Al_2O_3 membranes possessed the range of linear drying and firing shrinkage of 8.5–11.5 and 0–0.75%, respectively. After sintering at 1300°C, all the tubular Al_2O_3 membranes showed pore diameters ranging from 0.1 to 10 μm. The small Al_2O_3 powder at 20 wt% content demonstrated the considerable potential as membrane due to the beginning of connected pore network from their sintering. The method of agar gelcasting combined with the acetone-assisted drying offered a new alternative for forming the tubular Al_2O_3 membranes with simplicity and economy replacing the use of expensive extruder together with particularly suitable binder.