Structural analysis of bioactive glasses

In this study four series of single and mixed alkali glass systems were made and investigated using MAS NMR. Additionally the densities of the glasses were measured experimentally, as well as calculated theoretically using Doweidar’s model. MAS NMR was used to obtain a quantitative structural understanding of glasses by calculating the concentrations of bridging and non-bridging oxygens per silicon oxygen tetrahedron as a function of the alkali oxide concentration expressed as Qn. 29Si MAS NMR spectra exhibited a single resonance corresponding closely with Si in a Q2 state. The chemical shift of the 31P MAS NMR peak was attributed to phosphate in an orthophosphate environment. The 29Si NMR spectra are in agreement with the density data. Using Doweidar’s model the proportions of Q2 and Q3 were calculated, showing that all glasses studied are predominantly Q2 in structure, i.e. [ SiO 3 - ] n silica chains which readily dissolve. The changes in the chemical shifts of the Q2 and Q3 species with composition have been interpreted as resulting from the preferential association of Na+ with Q3 and Ca2+ with Q2.