Structural characterisation of fluorine containing glasses by 19F, 27Al, 29Si and 31P MAS-NMR spectroscopy

Fluorine containing glasses are important components for glass ionomer cements. Their main advantage is the long-term fluoride release during application. This paper deals with the MAS-NMR structural characterization of a series of fluorine containing glasses that could possibly be used for glass ionomer cements and they are based on the following composition: (1.5)SiO(2)center dot Al(2)O(3)center dot(0.5/0.25)P(2)O(5)center dot(1 - Z - Y)CaO center dot(0.5)CaF(2)center dot(Z)SrO center dot(Y)Na2O, where X=0.5, Y=0.0 or 0.2 and Z=0.0, 0.8 and 1.0. In some of the glasses, CaO is replaced with SrO that gives radio-opacity to the final glass ionomer cement. Si-29 MAS-NMR spectra gave strong evidence for the presence of Q(4)(4Al) and Q4(3Al) species. Al-27 MAS-NMR spectra showed the presence of largely Al(IV) and a smaller proportion of Al(VI) particularly in glasses with high phosphorus content. There is evidence for the presence of [P-(OAl)(n)(4 - n)O]((4-n)-) species. In low sodium containing glasses, the principal P species was Al-O-PO43-. The presence of sodium and the low phosphorus content favored amorphous phase separation as shown by the P-31 MAS-NMR spectra and the presence of orthophosphate, especially in the case of glasses with low phosphorus content. The main species observed by F-19 MAS-NMR spectra were F-Ca/Sr(n) and Al-F-Ca/Sr(n), however when Na,O was present a weak peak attributed to Al-FNa(n) was also present reflecting the low sodium content of the glasses. (c) 2005 Elsevier B.V. All rights reserved.