Effect of Pillar Density on Micropore Volume and Thermal Durability of Alumina Pillared Fluorine Micas

Abstract

Layer charge of expandable Na-fluorine micas can be controlled by utilizing Al³⁺- f ixation into the hexagonal silicate holes. This also results in controlling the cation exchange capacity of host fluorine mica crystals. The layer charge controlled fluorine micas were reacted with the hydroxoaluminum solution containing a polynuclear complex, which was obtained by the reaction with zeolite. The hydroxoaluminum ion-mica composite thus formed have controlled intercalated Al-content, i. e. the controlled pillar density, corresponding to the variation of layer charge of host crystals. Effect of pillar density on micropore volume and thermal durability has been clarified for the pillared fluorine micas formed by heating at 200∼700°C for 1 h; Thermal durability of the pillared micas increased with pillar density. High specific surface areas (Langmuir) of 366 m²/g at 600°C of heating temperature and 226 m²/g even at 700°C were preserved in the high pillar density mica (1.58 mol Al/Si₄O₁₀). The micropore volume ofthe pillared micas depended on pillar density and heating temperature, indicating that appropriate pillar density and thermal treatment were essential for high micropore volume (ca.0.1 ml/g). The micropore size distribution obtained by the micropore analysis (MP method) also showed the dependence of pillar density.