Étude RMN du silicium-29 et de l'aluminium-27 dans la solution solide mullite Al₂(Al_2+2xSi_2-2x)O_10-x

CNRS, Centre de recherches sur la physique des hautes températures, 1D, av de la Recherche-scientifique, 45071 Orléans Cedex 2, France.

Abstract

The ²⁹Si MAS NMR study has shown the existence of four different sites for Si whatever the composition of mullite. Their populations evolve linearly with the composition in the solid solution. The major site, not reported in precedent studies due to its broad distribution of chemical shifts, increases as 2x, x being the number of oxygen vacancies. It is assigned to all the tetrahedra near an oxygen vacancy. By extrapolation it is not present in sillimanite (x = 0). Two other sites are modified sillimanite-type sites and decrease as lx.

The ²⁷Al MAS NMR study has been carried out at two different magnetic fields (7 and 11.7 T). The spectra have been simulated with quadrupolar bands and show that the Al(IV)/Al(VI) ratio decreases abnormally for alumina-rich mullites. The ²⁷Al NMR is not quantitative. Particularly the most distorted tetrahedra. more present in the alunina-richer millites, are only partially seen by NMR.