Solvothermal synthesis of germanosilicate-sodalite and silica-sodalite: Effects of water, germanium and fluoride

The crystallization of silica-sodalite (SOD) in ethylene glycol solutions at 453 K has been investigated in the absence and presence of water, germanium dioxide and ammonium fluoride. In the systems studied, water at small amounts acts as an additional solvation agent to ethylene glycol, and does not significantly affect sodalite crystallization. At high contents that exceed the molar values equivalent to SiO2, water privileges a formation of the most dense crystalline silica phase, α-quartz. In contrast, presences of germanium and fluoride species favor the crystallization of silica-based materials having the SOD framework structure, which possesses a lower framework density than quartz. An interplaying relationship of these three species has been found and discussed.