THE USE OF SI-29 MAS-NMR AND MONTE-CARLO METHODS IN THE STUDY OF AL SI ORDERING IN SILICATES/

The use of Si-29 Magic Angle Spinning NMR to provide information about the local structure and order about the SiO4 tetrahedra in framework silicates is reviewed. A number of problems, including difficulties of peak assignment and the necessity to measure accurate intensities of the weakest peaks in the NMR spectra, are discussed. Si-29 MAS-NMR can be used to determine the number of Al-O-Al linkages in the structure, but the sensitivity of the final answer to experimental errors can le ad to absurd results. A new method, involving an inverse Monte Carlo a lgorithm, to analyse Si-29 MAS-NMR data for silicates with long-range Al/Si disorder is described, and illustrated with examples of Cs-leuci te, analcime, and annealing measurements for cordierite. (C) 1997 Else vier Science B.V.