MAS-NMR studies of glasses and glass-ceramics based on a clinopyroxene-fluorapatite system

作者：Abo Mosallam H A; Hill R G; Karpukhina N^*; Law R V

来源：Journal of Materials Chemistry, 2010, 20(4): 790-797.

DOI：10.1039/b915573b

Glasses and glass-ceramics based on the ternary system CaMgSi(2)O(6)-NaAlSi(2)O(6)-Ca(5)(PO(4))(3)F (diopside (Di)-jadeite (Jd)-fluorapatite (FAp)) have been studied using magic angle spinning (MAS) NMR, powder X-ray diffraction (XRD) and thermal calorimetry. In this silicate system Na(2)O and Al(2)O(3) have been progressively substituted for CaO and MgO: (CaMgSi(2)O(6))(1-x)-(NaAlSi(2)O(6))(x)-(Ca(5)(PO(4))(3)F)(y) where 0 <= x <= 30 mol% and y = 7 mol%. (29)Si MAS-NMR of the glasses showed a peak corresponding to a mixed Q(2)/Q(3) silicate species which slightly decreased in chemical shift on increasing Na(2)O and Al(2)O(3) substitution. After heat treatment of the glasses two major crystalline phases: a silicate solid solution (clinopyroxene) and FAp have been identified by XRD, with the silicate phase crystallising out first. A glassy phase coexisted with these crystalline phases and became more evident with increasing Na(2)O and Al(2)O(3) content. As expected, no crystalline Jd has been found from XRD or MAS-NMR. (27)Al MAS-NMR spectra of the glasses shows only Al(IV) to be present on addition of Al(2)O(3). Upon heat treatment, a new, sharp Al(VI) peak at -4 ppm assigned to the solid solution was observed, which corresponds to Al(3+) in a six coordinate state, replacing Mg(2+) along the crystalline silicate chain structure with the replacement of either an additional Mg(2+) or Ca(2+) by Na(+) to maintain the charge balance. The amount of Al(VI) formed on heat treatment grows linearly with addition of Al(2)O(3), but does not exceed ca. 20% from the total aluminium concentration present in the system. The signal from the Al(IV) in the heat treated material belongs to the residual aluminosilicate glassy phase. (31)P MAS-NMR shows the presence of mixed calcium/magnesium/sodium amorphous orthophosphate species in the glass, which upon heat treatment, changes to crystalline Ca(5)(PO(4))(3)F. (23)Na MAS-NMR of the heat treated glass-ceramics shows a Jd-like environment at the lowest Na(2)O and Al(2)O(3) content. This site gets increasingly disordered with increasing Na(2)O and Al(2)O(3) content, which is reflected in the changing (23)Na MAS-NMR shift.

• 出版日期2010