Characterisation of fluorine containing glasses and glass-ceramics by 19F magic angle spinning nuclear magnetic resonance spectroscopy

Abstract

19F magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy was used to characterise the local environment of fluorine in three types of fluorine containing glass-ceramics. The glass-ceramic compositions studied included four that crystallised to fluorcanasite, one which crystallised to barium fluorphlogopite and one which crystallised to fluorrichterite. In the fluorcanasite glasses, prior to crystallisation, the fluorine was present solely as an F–Ca( n) species whilst following crystallisation it was also present as an F–Ca( n) species in the fluorcanasite phase and in those glasses containing AlPO 4 it was also present as an F–Ca( n) species in fluorapatite. In the fluorrichterite and fluorphlogopite glasses the fluorine was present predominantly as F–Mg(3) and following crystallisation it was also present as F–Mg(3) in the fluorrichterite and fluorphlogopite phases. In all these glass-ceramics fluorine appears to be preferentially associated with the cations of highest charge to size ratio and the local environment of fluorine in the glass and the crystal phase is almost identical.