Al,Si ordering on cordierite using “magic angle spinning” NMR |
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| Authors: | Andrew Putnis Colin A Fyfe Gian C Gobbi |
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| Institution: | 1. Department of Earth Sciences, University of Cambridge, CB2 3EQ, Cambridge, England
2. Department of Chemistry, University of Guelph, N1G 2W1, Guelph, Ontario, Canada
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| Abstract: | Silicon-29 “magic angle spinning” nuclear magnetic resonance (NMR) spectroscopy has been used to study the changes in local Si environment during Al, Si ordering in synthetic cordierite, Mg2Al4Si5O18. In the most disordered form, crystallized from a glass, eight distinct tetrahedral sites for silicon can be identified and assigned, while there are only two distinguishable Si sites in the well-annealed ordered form. This allows the changes in the Si site environments to be determined as a function of annealing time for the transformation from the disordered to the ordered form. The first crystallized state has a considerable degree of partitioning between T1 and T2 sites with the following site occupancies: T1 ? Al:Si=0.80:0.20, T2?Al:Si=0.27:0.73 The changes in Si environment are approximately linear with log time. The measured values of 29Si isotropic chemical shift do not fit well to previously determined correlations of shift with various structural parameters. |
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