Quantitative structural analysis of mullite by 27Al nuclear magnetic resonance satellite transition spectroscopy.

27Al Nuclear magnetic resonance (NMR) satellite transition spectroscopy has been used for the quantitative investigation of the microstructure of polycrystalline 2/1-type mullite (approximately 76 wt.-% Al2O3 and 24 wt.-% SiO2). Using this method the chemical shifts, quadrupole interaction parameters and relative amount of Al in the various coordination polyhedra have been obtained with high accuracy. The additional suppression of second-order quadrupolar broadening of the 27Al magic-angle spinning (MAS) spinning sidebands of the inner satellite transitions allows three different AlO4 units to be detected. The three AlO4 resonances with isotropic chemical shifts at 68, 53 and 45 ppm are associated with AlO4 polyhedra in the tetrahedral double chains [AlO4(T)], the tetrahedra adjacent to the oxygen vacancies [AlO4(T*)] and the tetrahedra AlO4(T') linked by Oc* with AlO4(T*), respectively. Our NMR study of a polycrystalline sample supports the results of previous single-crystal studies of Angel et al. [Am. Mineral., 76 (1991) 332], especially the exclusion of silicon from the tetrahedral sites linked by Oc*.