Structural characterization of ionomer glasses by multinuclear solid state MAS-NMR spectroscopy

In the present study we report the results of Si-29, Al-27, P-31 and F-19 magic angle spinning nuclear magnetic resonance spectroscopy (MAS-NMR) of 4.5SiO(2)-(Al2O3)-Al-3-1.5P(2)O(5)-(5-z)CaO-zCaF(2) glasses with z = 0-3 to elucidate the effect of fluoride content on the glass structure. The 29Si MAS-NMR spectra gave a chemical shift of about -90 ppm corresponding to Q(3)(3Al) and Q(4)(3Al). The Al-27 MAS-NMR showed a large broad central peak around 50 ppm, which is assigned to four-coordinated Al linked via oxygen to P. A shoulder around 30 ppm and a small peak at about 0 to -10 ppm appeared in the 27 Al MAS-NMR spectra of the glasses on increasing the fluoride content assigned to five-coordinated and six-coordinated Al species, respectively. The P-31 MAS-NMR spectra indicated the presence of Al-O-P bonds. The P-31 chemical shift decreased with increasing fluoride content as a result of calcium being complexed with fluoride. This resulted in a reduction of the number of available cations to charge balance non bridging oxygens in phosphorus and an increase in the number of Al-O-P bonds being formed, instead. The F-19 spectra indicated the presence of Al-F-Ca(n) and F-Ca(n) species in all the glasses containing fluoride as well as an additional Si-F-Ca(n) species in the glasses with higher fluoride content. Published by Elsevier B.V.