Study of the alkaline environment in mixed alkali compositions by multiple-quantum magic angle nuclear magnetic resonance (MQ–MAS NMR)

45S5 Bioglasses of the composition 46.1 SiO2–2.6 P2O5–26.9 CaO–(24.4 − x) Na2O–xMe2O (Me = Li or K) have been investigated using MAS NMR and MQ–MAS NMR methods. The analysis of the 29Si MAS NMR spectrum revealed two lineshapes whose chemical shift is consistent with two silica Qn=2,3 species. The 31P MAS NMR spectrum reveals the effect of both Na and Ca ions. The chemical shift of the observed 31P signal is intermediate between those of Na3PO4 (near 10 ppm) and Ca3(PO4)2 (near 3–0 ppm) species. The 23Na MAS NMR spectra were observed in the alkali oxide composition: 24.4 Na2O, 12.2 Na2O–12.2 K2O and 12.2 Na2O–12.2 Li2O. The substitution of Na with Li or K was done to determine the extend of alteration of the glass structure. This goal was best accomplished by 23Na MQ–MAS NMR. The two-dimensional spectra revealed three sites in the 24.4 mol% Na2O glass. These sites were not resolved in the 1D MAS NMR spectroscopy. In the mixed glasses, only two sites were obtained.