Study of Dehydration of Natrolites in Hydrous Environment Using In-situ X-ray Powder Diffraction

This study systematically compares the thermal stability and phase transition behavior of natrolite (NAT) in aqueous and anhydrous environments as a function of the extra-framework cation (EFC)'s hydration energy and ionic radius.High-temperature in situ X-ray diffraction experiments were conducted on Na-, K-, and Cs-exchanged NAT samples, and the transition temperatures and thermal expansion coefficients were analyzed.Na-NAT, with the highest hydration energy and the smallest ionic radius, exhibited a significant delay in phase transition up to 475 C under aqueous conditions.K-NAT showed an intermediate delay, while Cs-NAT, having the lowest hydration energy and the largest radius, exhibited the lowest transition temperature regardless of water presence.Thermal expansion behavior followed similar trends: Na-NAT showed positive expansion before dehydration, while K-and Cs-NAT exhibited negative thermal expansion even before the transition.This study reveals that the physicochemical properties of EFCs critically affect the thermal behavior of natrolite, suggesting their potential utility in designing zeolite-based materials for high-temperature applications.