Thermal analysis of fluorine containing gels and precursors of high silica zeolites

Abstract

By means of simultaneous DTA-, TG-and DTG-technique, the silicate gels and the MFI crystals obtained from these gels have been investigated. The gels have been prepared in presence and in absence of tetrapropylammonium cation (TPA t) and with Li t, Na t, NH~ and K t fluorides. In absence of TPA t no thermal effects have been observed in Li t-and Nat-gels. The effects observed in the NH~ -gel stem from a decomposition and release of inorganic phases: SiF4, NH4F, NH3. The DTA/DTG effects in the TPA t containing gels and in the MFI crystals of monodisperse size are attributed to the decomposition of TPA t cation. It can be concluded from these effects that the interaction between the gels and the TPA t cation is rather weak. The interaction between TPA t and MFI crystals obtained in fluoride medium is stronger than the interaction with crystals obtained from alkaline media. Similar thermal effects are obtained after grinding the long crystals to those having a large distribution of crystal sizes.