STRUCTURE OF SYNTHETIC FRAIPONTITE

The structure of hydrothermally synthesized fraipontite was studied in comparison with that of natural fraipontite. Silicon-29 NMR showed a single peak at-83. 1 ppm (Fig. 1), which revealed much isomorphous replacement of silicon by aluminum. Fraipontite contained nearly equimolar aluminum in both tetrahedral and octahedral sheets (Fig. 2), hence the positive charge in the octahedral sheet was mostly compensated by the negative charge in the tetrahedral sheet. Essential water, which was not observed in natural fraipontite, was detected by differential thermal analysis (Fig. 3). The chemical analysis and silicon-29 NMR showed that the product contained ca. 90% of fraipontite (Table 3), whose composition is shown in equation (2). It was observed by the electron microscope (Fig. 4) that the fraipontite crystal was in the form of thin stacked plates, and exhibited a characteristic of phyllosilicates. IR spectrum (Fig. 5) indicated that both of the coordinating hydroxyl group and the essential water were in the state of hydrogen bonding. X-Ray diffraction indicated that the (001) spacing of synthesized fraipontite was almost same as that of natural fraipontite. These findings suggested that the essential water was present in the oxygen six membered ring of tetrahedral sheet (Fig. 6).