Characterization of local atomic environment and quantitative determination of changes in site occupancies during the formation of ordered synthetic cordierite by 29Si and 27Al magic-angle spinning n.m.r. spectroscopy

Abstract

Eight distinct tetrahedral sites for silicon can be identified and assigned in freshly crystallized (hexagonal) synthetic cordierite, Mg₂Al₄Si₅O₁₈, four in the chain manifold and four in the six-membered aluminosilicate rings, but there are only two sites (one in the rings, the other in the chains) in the aged (orthorhombic) product; Si:Al ratios within each manifold can be determined from the ²⁹Si magic-angle spinning n.m.r. spectra which also permit the course of Si, Al ordering to be charted as thermodynamic equilibrium is approached.