FTIR spectroscopy of framework aluminosilicate structures: carnegieite and pure sodium nepheline

In this work the spectroscopic studies of polymorph transformation of framework silicates containing six-membered rings and different Si/Al ratio were carried out. Two model systems with different stoichiometries (Na-LTA, Si/Al = 1 and Na-FAU, Si/Al = 1.23) were investigated. Thermally induced phase transformations of initial zeolites resulted in forming of stuffed derivatives of cristobalite (carnegieite) and tridymite (nepheline). Powder XRD method was used for the recognition of new phases. All obtained phases have framework structures built by single six-membered rings. The changes of middle range order (rings symmetry), which take place during transformations of Na-LTA and Na-FAU into low-temperature carnegieite, low-temperature carnegieite into pure sodium (ps) nepheline as well as ps-nepheline into high-temperature carnegieite, were investigated by IR spectroscopy. The rings symmetry is found to be dependent on a phase stoichiometry as well as on polymorph type. (C) 2003 Elsevier Science B.V. All rights reserved.