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 Q(n). Si-29 MAS NMR spectra exhibited a single resonance corresponding closely with Si in a Q(2) state. The chemical shift of the P-31 MAS NMR peak was attributed to phosphate in an orthophosphate environment. The Si-29 NMR spectra are in agreement with the density data. Using Doweidar's model the proportions of Q(2) and Q(3) were calculated, showing that all glasses studied are predominantly Q(2) in structure, i.e. [SiO3-](n) silica chains which readily dissolve. The changes in the chemical shifts of the Q(2) and Q(3) species with composition have been interpreted as resulting from the preferential association of Na+ with Q(3) and Ca2+ with Q(2). (C) 2004 Published by Elsevier B.V.