Effect of temperature on hydrothermal synthesis of analcime and viseite

The zeolite minerals analcime (Na-16(Al16Si32O96). 16H(2)O) and viseite (Na2Ca10(Al20Si6P10O60(OH)(36)). 16H(2)O) were synthesized by hydrothermal treatment of artificial glasses of the respective same composition in a temperature range between 80 and 630 degrees C at 100 MPa H2O pressure. The crystal symmetry of both zeolites varied systematically with temperature under the given experimental conditions, starting from orthorhombic symmetry at low synthesis temperatures, tetragonal at medium leading to cubic symmetry at highest zeolite synthesis temperatures. The crystal sizes varied between 500 nm and 100 mu m. In case of analcime water free tectosilicates instead of zeolites were formed at T greater than or equal to 500 degrees C while viseite was formed up to 630 degrees C. The investigations showed the direct correlation between chemical composition of the starting materials and the formed zeolite phase under the given p-T conditions. (C) 1999 Elsevier Science S.A. All rights reserved.