Effect of P2O5 content in two series of soda lime phosphosilicate glasses on structure and properties -: Part I:: NMR

The effect of the variation in phosphate (P2O5) content on the structure of two series of bioactive glasses in the quaternary system SiO2-Na2O-CaO-P2O5 Was studied. The first series (1) was a simple substitution of P2O5 for SiO2 keeping the Na2O:CaO ratio fixed (1.00:0.87). The second series was designed to ensure charge neutrality in the orthophosphate (PO43-), therefore as P2O5 was added the Na2O and CaO content was varied to provide sufficient Na+ and Ca2+ cations to charge balance the orthophosphate present. The glass network connectivity (NC) was calculated for each glass and a modification for the presence of a separate P2O5 phase was included (NC') P-31 and Si-29 magic-angle-spinning nuclear magnetic resonance (MAS-NMR) spectroscopy was performed on glass series I and II to determine the structural units present and their relation to glass properties. (31)p MAS-NMR spectra of series I resulted in a broad resonance around 9 ppm corresponding to orthophosphate in an amorphous environment. The 9.25 Mol% P2O5 glass shown to be partially crystalline by X-ray diffraction was heat treated, and the (31)p MAS-NMR spectrum showed a sharp peak around 3 ppm corresponding to calcium orthophosphate or sodium pyrophosphate and overlapping broader peaks at 8.5, 10.5 and 14 ppm possibly corresponding to two mixed calcium-sodium orthophosphate phases and amorphous sodium orthophosphate respectively. P-31 MAS-NIMR spectra of series II resulted in a broad resonance around 10.5 ppm corresponding to orthophosphate in an amorphous environment. Si-29 MAS-NMR spectra of glasses from series I showed a shift in the resonance peak from around -78 to -86 ppm indicating an increase in Q species in the glass and a reduction in Q with phosphate addition confirming the presence of orthophosphate. The heat treated sample showed a sharp Si-29-NMR resonance at -88 ppm, indicating a crystalline Q(2) six-membered combeite (Na2O center dot 2CaO center dot 3SiO(2)) silicate-type phase, which was confirmed by powder X-ray diffraction. Si-29 MAS-NMR spectra of glasses from series II showed no shift in the resonance at around -78 ppm across the series, confirming an orthophosphate environment. (C) 2008 Elsevier B.V. All rights reserved.