ANALYSIS OF LOCAL CATION ARRANGEMENT IN MULLITE USING SI-29 MAGIC-ANGLE-SPINNING NUCLEAR-MAGNETIC-RESONANCE SPECTRA

Local cation arrangements for mullites with various chemical compositions were examined using Si-29 magic-angle spinning nuclear magnetic resonance (MAS NMR) spectra and the X-ray Rietveld method. The structure of mullite was refined using the Rietveld method, and the relations between chemical composition and lattice constants were revised. Si-29 NMR spectra of mullites showed a main resonance at -86 ppm accompanied by weak resonances at -94, -90, and -81 to -82 ppm. These resonances were assigned to each local cation arrangement of TO4 tetrahedra in mullite by calculating the chemical shift according to Sherriff and Grundy's method. The resonances at -81 to -82 ppm were assigned to the arrangement of the T(Si), T(Al)-O(c)*-T*(Al) cluster, which has been considered to be rather unusual, and their population was found to increase with increase in the Al2O3 content in mullite.