Abstract:

In this study, the coordination structure of Al³⁺ in CaO-Al₂O₃-SiO₂ aluminosilicate glasses (CAS) was studied using solid-state ²⁷Al and ²⁹Si magic-anglespinning NMR. The results showed that: 1). most Al³⁺ ions in CAS aluminosilicate glasses are present in the form of AlO₄ tetrahedra, and act as networkforming ions. A small part of Al³⁺ ions exist as network-modifying cations in the forms of six-, five- and other- coordinated aluminum. 2). O_nb/T is inversely proportional to η, where O_nb/T is the number of non-bridge oxygen atom per tetrahedra, and η is the ratio of the number of tetrahedral Al³⁺ to the total number of Al³⁺ in the region of interest (ROI). The slope of the O_nb/T vs.η relationship is influenced by γ, where γ is the ratio of the total number of Al³⁺ to the total number of Si⁴⁺ in the ROI.

Key words: NMR, magic angle spinning, aluminosillicate glasses,  27Al, 29Si