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Th2 reciprocal salt pair Sr,SiOl-Sr,GeO*-Ba,Ge04-Ba,SiOl was investigated using X-ray powder diffraction and DTA. Unlimited solubility in the lOW-&S04 structure type ( a ' ) occurs throughout the system above 85°C. The nonlinear changes of some lattice constants of the solid solutions are discussed. A stable monoclinic low-temperature ( p ) form of Sr,SiO, was found which converts reversibly to the high-temperature d-modification at 85'C. The enthalpy of the P-N' transition is 51 cal/mol. In the reciprocal salt pair the p-form solid solutions occur in a very narrow region below 85°C.

Large crystals of ZSM-5 have been dealuminated by several methods in order to compare the effectiveness of the various treatments and their influence on the crystal structure. Any acidic treatment always leads to a partial dealumination of the aluminosilicate framework. The extracted aluminium cannot be completely removed from the crystals. Some of it remains inside the pores, presumably as aloxo compounds. The largest fraction of aluminium can be removed from the crystals of ZSM-5 by leaching with an acid followed by steaming and a subsequent final acid leaching. The steaming treatment aparently causes a re-ordering within the crystal structure by removing the framework vacancies by the T-jump mechanism. Ion exchange of AI3+ by using aqueous solutions of Al salts is impossible.