Thermally induced structural and microstructural evolution of barium exchanged zeolite A to celsian

摘要

A sample of Ba-exchanged zeolite A was thermally treated at temperatures up to 1400℃ and its structural and microstructural evolution was investigated by room temperature X-ray diffraction, IR spectroscopy and SEM observations. The following are the main results: the zeolite structure thermally collapses at 200℃ by a partial disruption of the D4R units. Thermal treatments in the temperature range 200-400℃ result in a middle-range order which favors the crystallization of small crystallites of monoclinic celsian at 500℃. Thermal treatments in the temperature range 500-800℃ do not give rise to the crystalline growth of monoclinic celsian, whereas crystallization of hexacelsian occurs above 800℃. At temperatures not lower than 1000℃ hexacelsian begins to convert into monoclinic celsian. The conversion is completed by thermally treating the sample at 1400℃ for 22 hours.