A high-energy X-ray diffraction, P-31 and B-11 solid-state NMR study of the structure of aged sodium borophosphate glasses

The structure of aged melt-quenched sodium borophosphate glasses of composition (P2O5)(40)(B2O3)(x)(Na2O)(60-x) (with x in the range 10-40) has been studied by high-energy X-ray diffraction (HEXRD), P-31 and B-11 magic angle spinning (MAS) NMR. Similar to the fresh samples, both P-O-P and P-O-B linkages are found to be present in these glasses. All three techniques show that the cross-linking between borate and phosphate units increases with boron oxide content. Distinctively upon aging, the glass is found to hydrolyze causing the network to degrade. At the same time, crystalline phases are now also observed. XRD and DTA show that the samples have a higher tendency towards crystallization with increasing boron oxide content upon exposed to moisture. P-31 and B-11 MAS NMR results are in agreement with these findings. TGA data show that samples with higher boron oxide content take up more moisture upon aging, suggesting that crystallization may be associated with glass hydrolysis. HEXRD results also suggest that sodium ions are preferentially associated with borate units with increasing boron oxide content. (C) 2008 Elsevier B.V. All rights reserved.