Zeolite-type and nepheline crystals in glass-ceramics

Abstract

Zeolites are hydrated alumino-silicates. They crystallize in framework structures. Zeolites are used in the catalysis, adsorption, drying and separation teehnologies. Glass-ceramies are polycrystalline solids prepared by controlled crystallization of glasses, with interesting properties. A new field of application can be opened by combination of the properties of zeolites and glass-ceramics. For example, material surfaces can be functionalized (membranes, foams) or special geometries for catalysis can be stabilized. It is possible to design glass-ceramics with a zeolite as crystal phase. In this study further investigations of the phase distribution and the interface between the crystal phases will be presented. Glasses with a composition similar to the stoichiometric composition of a zeolite were melted with partial subtitution of NaF for Na2CO3. Samples of these glasses were crystallized at various temperatures. The zeolitic phase Na6[AlSiO4]6 and the nepheline were precipitated in two of the glass compositions at all crystallization temperatures. Na6[AlSiO4]6 is a zeolite of the sodalite type. The interface between the zeolite and the nepheline will be shown. The nepheline seems to grow radially (epitaxially) on the zeolite. The obtained zeolite does not correspond to the synthesis compositions of the glasses.