Anomalous compression of scolecite and thomsonite in aqueous medium to 2 GPa

摘要

The high-pressure behaviour of fibrous zeolites scolecite and thomsonite in penetrating aqueous medium was studied using in situ synchrotron powder diffraction data from diamond anvil cell. Both zeolites exhibit anomalous compressibility due to an additional pressure-induced hydration of structure channels. At 1.23 GPa, scolecite undergoes transformation to high-hydrated phase, which is expanded by 5.0percent as compared to original scolecite due to the increase of zeolitic water content from 3 to 4.6 molecules per formula unit. The compressibility of thomsonite is markedly lower than that reported previously, where a nominally penetrating medium with 6percent H_(2)O was used. This indicates to an additional hydration under high pressure, which is confirmed by the observed phase transition in thomsonite. The over-hydration effect in fibrous zeolites seems to largely depend on partial water pressure in compressing medium.