Potassium merlinoite: crystallization, structural and thermal properties

The crystallization of merlinoite and chabazite, the main zeolitic phases obtained from KOH type aluminum-silicate gels, can be controlled by the K+ concentration. A high K+ concentration in the gel is the key factor to facilitate the formation of pure merlinoite. A structure formed by a hydrogen-bound potassium water network acts as an inorganic template in the crystallization of merlinoite. This potassium water structure is also stabilizing the structure of the as-synthesized crystals, Removal of this water results in a major structural deformation of merlinoite. High purity merlinoite has been synthesized from potassium rich aluminum-silicate gels by two different synthesis routes: by adding K+ in the form of KOH or in the form of KOH and KNO3. Addition of KNO3 to the gel seems to improve the quality of the merlinoite phase formed: a higher quality diffraction XRD pattern and larger and more regular crystals are obtained. Equally, the Si/Al ratio of the crystals is increased, The compositions of the most crystalline samples are: KOH-mer: K-11.5[A(11.5)Si(20.5)O(64)] . 15H(2)O, KNO3 -mer: K-9.5[Al9.5Si22.5O64]. 13H(2)O. (C) 2001 Elsevier Science B.V. All rights reserved.