Formation process of Sr-celsian from precursor zeolites

Two kinds of zeolites with different crystal structures with the same chemical composition of SrO center dot Al2O3 center dot 2SiO(2)center dot xH(2)O prepared by an ion-exchange technique were used as a precursor of Sr-celsian. One was Sr-exchanged zeolite A (Sr-A), the other was Sr-exchanged Linde F zeolite (Sr-F). The Sr-A almost became an amorphous material at 400 degrees C, and then generates a small amount of Sr-hexacelsian from the amorphous material at 500 degrees C. The amount of Sr-hexacelsian steeply increased and a small amount of Sr-monocelsian also formed at 1000 degrees C. On the other hand, the Sr-F nearly becomes an amorphous material at 300 degrees C, and then Sr-hexacelsian mainly formed along with a small amount of Sr-monocelsian above 1000 degrees C. In both of the Sr-exchanged zeolites, a single phase of Sr-monocelsian was obtained finally at 1300 degrees C, owing to the hexacelsian - to - monocelsian phase transformation. The reason for the crystallization of Sr-hexacelsian at 500 degrees C only from Sr-A was explained in terms of the similarity in framework structures (of zeolite A and Sr-hexacelsian. (C)2009 The Ceramic Society of Japan. All rights reserved.