Synthesis, properties and structure of ion exchanged hydrosodalite

摘要

Alkali metal and alkali-earth metal hydrosodalites with the formula M-6[AlSiO4](6).8H(2)O (M=Li, Na, K, Mg, Ca, Sr) have been prepared by ion exchange of Na-6[AlSiO4](6).8H(2)O using a solution of the appropriate metal nitrate solution under reflux for a period of 24h. The starting materials and products were characterized using a combination of techniques including IR, DSC, TGA, ICP, AA, MASNMR and X-ray diffraction. The alkali metal and alkali-earth metal hydrosodalites crystallize with the primitive cubic sodalite unit cell and an ordered AlO4/SiO4 framework in the space group P43n with cell parameters lying between 8.8 and 9.2 Angstrom. The structures of these materials have been refined using powder X-ray diffraction data in order to delineate structural changes as a function of the occluded cation. Temperature-dependent powder X-ray diffraction has been used to observe changes in the structure as a function of temperature. Results from the DSC and TGA analysis show that the temperature at which water is lost from the beta cages is a two-stage process. In the second stage, the temperature rises as the size of occluded cation increases, implying that the presence of a larger cation in the six-ring window blocks the path of the exiting water molecules. (C) 2003 Elsevier Inc. All rights reserved.