Large-scale production of alkali-resistant Shirasu porous glass (SPG) membranes: Influence of ZrO 2 addition on crystallization and phase separation in Na 2O–CaO–Al 2O 3–B 2O 3–SiO 2 glasses; and alkali durability and pore morphology of the membranes

Abstract

To develop the large-scale production of alkali-resistant Shirasu porous glass (SPG) membranes based on phase separation and subsequent acid leaching, the crystallization and phase separation in mother glasses in the NaO–CaO–Al 2O 3–B 2O 3–SiO 2 system containing ZrO 2 were investigated. A crystalline phase of wollastonite (CaSiO 3) was formed in the ZrO 2-free mother glass heat-treated at approximately 900 °C, corresponding to the glass-shaping temperature. This crystallization was induced by the phase separation in the mother glass. The crystallization tendency was reduced by adding ZrO 2 to the mother glass due to an increase in the glass viscosity, and there was no crystallization in the mother glass with 3.5 mol.% ZrO 2. SPG membranes containing 3 mol.% ZrO 2 were successfully prepared from the mother glass with 3.5 mol.% ZrO 2 by the phase separation of the mother glass at 700–760 °C and subsequent acid leaching with a 0.5 mol dm −3 hydrochloric acid. The membranes had an interconnected pore structure over a wide pore diameter range of 0.1–10 μm. The membrane pore diameter increased with increasing heat-treatment temperature and holding time during the phase-separation process for the mother glass. The alkali resistance of the membranes was about 3.5 times higher than that of conventional SPG membranes.