Structure of natural water-containing glasses from Lipari (Italy) and Eastern Rhodopes (Bulgaria): SAXS, WAXS and IR studies

Two natural water-containing glasses with rhyolite composition originating from two different areas (perlite from Lipari, Italy, and expanded perlite from the Eastern Rhodopes, Bulgaria) have been characterised for chemical composition, atomic structure and specific surface area, with the ultimate goal of exploitation of volcanic glasses as carriers for heterogeneous metal catalysts. The two samples have similar chemical composition and total water content. The local structure, as determined by radial distribution function analysis of the wide angle X-ray scattering patterns, is similar, the medium-range structure being slightly more ordered for the Lipari glass. These results are confirmed by infra-red spectroscopy (IR) in the mid-IR range. Based on the small-angle X-ray scattering data we conclude that both glasses have a specific surface area of about 1 m(2)/g. The pore size distribution cannot be determined by our experiments because the two patterns are already asymptotic at the smallest attainable scattering angles. (C) 1998 Elsevier Science B.V. All rights reserved.