Concentration phase transitions in natural zeolite chabazite

The structure of the sublattice of guests in natural zeolite chabazite Ca-2[Al4Si8O24] (.) nH(2)O was studied by the H-1 NMR method over a wide range of zeolite water concentrations (1.5 less than or equal to n less than or equal to 12.8). At n < 1.8, water molecules only participate in ring diffusion close to Ca2+ ions localized in six-membered aluminosilicate rings. At n > 1.8, translational diffusion of H2O is observed. Changes in the character of water mobility are explained by the escape of some exchange Ca2+ cations from ion traps and the formation of [Ca(OH2)(x)](2+) aquacations in the volume of zeolite cavities. The localization of water molecules and Ca2+ ions was bimodal in character over the range of water contents from n approximate to 2 to approximate to 8.5. A concentration phase transition was observed at n(1) = 8.55. This transition was related to ordering of the guest substructure in the form of [Ca(OH2)(4)](2+) aquacomplexes. A similar transition at n(2) = 10.25 was related to the formation of [Ca(OH2)(5)](2+) complexes. The potential barriers to the diffusion of water molecules in chabazites with various water contents were determined.