Synthesis and Characterization of Fluormica Using Amorphous Silica Prepared from Serpentinite

Abstract

Several kinds of single-phase fluormicas were synthesized by solid reaction method using amorphous silica obtained from serpentinite by acid-treatment, and their expandable properties and the formation mechanism were discussed. Fluormica consisting of Mg, Si, N a, Li, O and F (Mg-mica) was prepared at 725-750° C for 1 hour by treating the mixture with molar ratio of SiO₂: MgO: NaF: LiF = 1.0: 0.5: 0.5: 0.25. By replacing Mg of Mg-mica with Al, Cu, Mn, Ni and Ti, substituted micas were synthesized at 750°C f or 1 hour. End membered mica was obtained only for Ni with the substitution of 75%. Partial replacement of 12.5-25.0% of Mg by the other elements resulted in t he formation of c orresponding single phase mica. Mg-mica and Al, Mn and Ti-substituted micas were found to be expandable by uptak ing mono layered water in the interlayered spaces, while Ni and Cu-substituted ones exhibited no expandable behavior. The crystallization of the amorphous silica into quartz during the formation of the substituted micas caused the restriction of the chemical composition of the products and was not allowed to drop their synthetic temperature.