Synthesis of Monoclinic Celsian from Ba-Exchanged Zeolite A.

Abstract

Two kinds of zeolites with different crystal structures with the composition of BaO Al 2 O 3 2SiO 2 xH 2 O prepared by an ion-exchange technique were used as a precursor of celsian. The difference between the zeolite structures resulted in the difference in modifications of celsian obtained through a heating treatment. Ba-exchanged zeolite A became an amorphous material at 300°C with dehydration, and then generates a small amount of monocelsian in the amorphous material at 500°C. When successively at 950°C for 1 h, hexacelsian formed in addition to the previously produced monocelsian. A single phase of monocelsian was obtained finally by heating at 1500°C for 8 h. The specimen heated at 1700°C, however, became a single phase of hexacelsian, owing to monocelsian-to-hexacelsian phase transformation. The structure of Ba-exchanged Linde F zeolite collapsed at 300°C with dehydration, and only hexacelsian formed at temperatures above 980°C. The reason for the formation of monocelsian only from Ba-exchanged zeolite A was explained in terms of the similarity in framework structures of zeolite A and monocelsian.