PHASE CHANGES AND AMORPHIZATION OF ZEOLITES AT HIGH PRESSURES: THE CASE OF SCOLECITE AND MESOLITE

Abstract

Pressure-induced amorphous-phase transitions (amorphization) have been observed in framework silicates like quartz and feldspars. A similar crystalline to highly disordered solid phase transition is reported in this study for two zeolites, scolecite and mesolite. Pressure-induced amorphization is demonstrated using in situ X-ray diffraction and Ra- man spectroscopy. Before complete amorphization, progressive structural changes are ob- served below 10 GPa. The transition from the crystal to the amorphous phase is irrevers- ible, and the pressure-quenched samples exhibit Raman spectra that bear strong resemblance to alumino silicate glasses obtained by quenching a liquid. In some cases, however, decom- pression from 15 GPa of fully amorphized samples is accompanied by a rim recrystalli- zation of the sample and preservation of an amorphous phase with a structure different from that quenched in other experiments. Shear stresses seem to have important control of the transformation occurring during the decompression of the samples.