Zeolites having STI-type framework

The ideal compositions for the end-members of this series are CagAli6Si560i44 58 H2O for stellerite, Na2CagAli8Si54Oi44-60 H2O for stilbite, and Nai6Ali6Si560i44-52 H2O for barrerite. The chemical formula for a natural stilbite was reported to be (Na,K) t(Ca,Mg)4+ Al c+8+2 Si28- -2y072 28 H2O with x 4.89 and -2.22 y 0.33 [78P1], There is no compositional gap between stilbite (monoclinic Na-rich phase) and stellerite (orthorhombic Na-poor phase). 

The thermal induced structural modifications of natural stellerite Ca8Ali6Si560i44-58 H2O, having Fmmm space group at RT, were analyzed by in situ experiments in the temperature range 302 K 976 K [06A1]. By 

The comparative analysis of the positional parameters of barrerite framework atoms between the samples studied by [75G3] and [99S1] displayed only minor differences. Differences in occupancy factors of almost all extra-framework sites were found between the two samples studied by [99S1]. The occupancy factors of Cl and W1 and the positional parameters of WIP and W4P rendered the strongest deviations with respect to those of the type locality sample. The cations in five C sites could not be located precisely. 

The modifications induced in barrerite structure were studied by firing a natural sample at 523.. 653 K for a few hours and then cooled at RT [78A1]. Phase B was obtained. The barrerite phase B maintained the same space group but the volume was reduced by 16 %, and there was a statistical breaking at 50 % of one oxygen 

The natural stilbite exchanged with NH was also transformed to the H-form by heating at 573 K for 12 h [97K1]. An increase of the sorption capacity was demonstrated. The most water molecitles, in H-stilbite, were lost by heating up to 673 K. Stmctmal collapse takes place at 823 K. 

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