Indicative significance of water environment in zeolitic structure – a study using experimentally grown cancrinite and analcime

Abstract

Cancrinite and analcime were synthesized in the two hydrothermal systems: acid plagioclase – Na₂CO₃ – H₂O and basic plagioclase – Na₂CO₃ – H₂O under widely varying temperatures and salt concentrations in the solution. The IR, ¹H MAS NMR, DTG/TG analyses were carried out to determine water position in the crystals. Additionally IR spectra were recorded during subsequent dehydration and rehydration processes. The results of the investigations indicate that the water environment in both minerals is sensitive to the conditions of crystal formation. Crystallization temperature is the most important factor influencing water position. The water sites in the analcime and cancrinite crystals depend on structure modifications. Variations of the structure result from different chemical composition of the source material, structure of the substrates and the salt concentration in the solution. The structures formed under lower temperatures incorporate more water than those formed at high temperatures. In the cancrinite and analcime two main types of water, H₂O(I) and H₂O(II), appear. Other OHm groups can also be recognized. The position of water H₂O(II) is better defined than that of H₂O(I). H₂O (II) is the most sensitive indicator of thermal conditions of the formation of cancrinite as well as analcime. The amount of H₂O(II) equals that of H₂O(I) in the products of low temperature (300°C) syntheses. In crystals synthesized at high temperature (550°C) the presence of H₂O(II) is very limited.