The dehydration process in the natural zeolite laumontite: A real-time synchrotron X-ray powder diffraction study

The dehydration process in the natural zeolite laumontite (Ca4Al8Si16O48. 18H(2)O, Z=1, C2/m, a=14.8066(9), b=13.1678(7), c=7.5389(5) Angstrom, beta=110.647(4) (degrees) at 310 K) has been studied in situ by means of powder diffraction using X-ray synchrotron radiation. The powder specimens was enclosed in a capillary and submerged in water, then intermittently heated to 584 K in temperature steps of 5 K, Each temperature was maintained for five minutes, while a full powder histogram suitable for Rietveld refinement was accumulated in a CPS120 position sensitive detector, The structure refinements of the 62 resulting powder datasets allow a complete analysis of the structure response to dehydration, The site occupancies of the water molecules in the zeolitic channels at each temperature are related to the anisotropic framework deformations and the changes in the cell volume, The changes in the coordination of the Ca cation and the variations in cation-framework oxygen bond distances are also interpreted on the basis of the cation-zeolitic water interaction. Major releases of water molecules from the structure are found at 349 K (W1 drops to 10% occupancy), at 370 K (60% of W5 is expelled), and in the temperature range 420-480 K (80% of W2 is gradually lost).