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 SiO 2-2.6 P 2 O 5-26.9 CaO-(24.4 À x) Na 2 O-xMe 2 O (Me = Li or K) have been investigated using MAS NMR and MQ-MAS NMR methods. The analysis of the 29 Si MAS NMR spectrum revealed two lineshapes whose chemical shift is consistent with two silica Q n=2,3 species. The 31 P MAS NMR spectrum reveals the effect of both Na and Ca ions. The chemical shift of the observed 31 P signal is intermediate between those of Na 3 PO 4 (near 10 ppm) and Ca 3 (PO 4) 2 (near 3-0 ppm) species. The 23 Na MAS NMR spectra were observed in the alkali oxide composition: 24.4 Na 2 O, 12.2 Na 2 O-12.2 K 2 O and 12.2 Na 2 O-12.2 Li 2 O. 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 23 Na MQ-MAS NMR. The two-dimensional spectra revealed three sites in the 24.4 mol% Na 2 O glass. These sites were not resolved in the 1D MAS NMR spectroscopy. In the mixed glasses, only two sites were obtained.