Johnson, Matthew N; (2003) Crystallographic studies of Clinoptilolite. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The work described in this thesis focuses on the ion exchange and structural properties of Clinoptilolite, whilst undergoing dehydration. Efforts have been made to understand the overall framework structure and to derive the coordination geometry around the cations at ambient, through dehydration to 600°C and finally on to collapse of the framework. Single crystal X-ray diffraction studies have identified three framework variations caused by dehydration and the effect of different ion exchanged cations. The first framework is the HEU topology, the second is the "heat collapsed" form of the HEU topology, and the third is a new framework transformation where the symmetry has lowered from monoclinic to triclinic. Energy Dispersive Diffraction (EDXRD) techniques have provided a detailed characterization of the unit cell changes of ion exchanged end members of Clinoptilolite from ambient to collapse temperatures (up to 1100°C). The results found match contemporary single crystal X-ray diffraction data collected up to 300°C. A detailed EXAFS and TGA study has also been carried out on different ion exchanged transition metal cations within the Clinoptilolite framework during dehydration. From this study it has been possible to identify the effect of water loss upon the coordination shells of transition metals and the relationship of the cations to framework structure.

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