Total understanding of the local structures of an amorphous slag: Perspective from multi-nuclear (29Si, 27Al, 17O, 25Mg, and 43Ca) solid-state NMR

Local environments of all constituent elements (Si, Al, O, Mg, and Ca) in an amorphous slag were examined using multi-nuclear solid-state NMR under high magnetic field (16.4 T). The amorphous slag framework structure can be generally described as a depolymerized, chain-like network of SiO4 tetrahedra branched with AlO4 tetrahedra. 17O multiple-quantum magic angle spinning (MQMAS) spectrum demonstrated that oxygens occupy structurally inequivalent sites, depending on their bonding nature. 25Mg and 43Ca MQMAS spectra also showed multi-site occupancy of the ions, and the average coordination numbers were estimated to about 6 and 7, respectively. Our results should underscore the impact of the high magnetic field NMR techniques, especially MQMAS, when applied to non-crystalline solids.