SAXS/WAXS and XAFS studies of zeolite stability

We show how combined synchrotron X-ray techniques like SAXS/WAXS can be used to chart the collapse of low density zeolites to form rigid alumino-silicate glasses of conventional density. The exothermal character of amorphisation is stressed and directly compared to the degree of crystallinity determined from WAXS and the density contrast contained in SAXS. The role of charge-compensating cations in destabilising the microporous structure can be determined from XAFS/XRD. The dynamics of the collapsing process obtained from all of these techniques are then contrasted with structural relaxation in the corresponding viscous alumino-silicate. It is concluded that temperature-induced zeolite amorphisation occurs on the time scale of glass relaxation between the glass transition and the strain point