THERMAL SHRINKAGE OF VARIOUS CATION FORMS OF ZEOLITE-A

The thermal shrinkage of Li, Na, K, Cs, ammonium, H, and Ca forms of z eolite A has been investigated by dilatometry up to 650 degrees C. The shrinkages of Li, Na, K, Cs and Ca forms are attributed to the dehydr ation and partial structural collapse which predominates over the norm al thermal expansion and cation migration from one site to another in the zeolitic structure. The ammonium form shows a noticeable shrinkage and a possible catalytic action of the acid sites produced in the zeo lite A in the combustion of ammonia evolved upon heating. The H form u ndergoes collapse at temperatures higher than 350-400 degrees C depend ing on the heating rate. (C) 1997 Elsevier Science B.V.