Synthesis of fluormica using silica sand by solid state reaction

Primary conditions for preparation of single-phase fluormicas were investigated by solid state reactions using silica sand. Mica was obtained as a single phase from the mixtures of SiO2 : MgO : NaF: LiF=1.0 : 0.5 : 0.35-0.5 : 0.25 at 725 degrees C for 3 h and at 750 degrees C for 1 h. Synthetic products were found to be 1Md type and expandable by uptaking monolayered water in the interlayer space. Furthermore, the effect of source of silica on the formation process was discussed, In the formation process of mica, the crystalline silicas such as alpha-quartz and cristobalite gradually decreased in amount by the reaction with some kinds of intermediate materials, and then were finally fixed in mica phase. When amorphous silicas, which easily transform into the crystalline silicas upon heating, were used as a silica source, single-phase mica was formed in a similar process as using crystalline silicas. However, in the case of amorphous silicas which crystallized slowly into cristobalite and alpha-quartz, single-phase mica was not obtained because intermediate materials would be existed in a definite temperature region.