Sol-gel synthesis of Na2O-Al2O3-P2O5 glasses and their characterization by NMR, SNMS, and AFM

Sodium aluminophosphate samples with composition 43.8Na(2)O center dot 12.5Al(2)O(3)center dot 43.8P(2)O(5) were prepared by the sol-gel route using different precursors and working in different pH ranges from pH < 1 up to pH > 10. The structures of the gels and of the corresponding glasses were investigated by solid state NMR and compared to that of a glass with the same composition prepared by a traditional melting process. In addition to bulk materials, thin films were deposited by dip coating on silica glasses. Applying secondary neutral mass spectrometry (SNMS), the expected elements and residual carbon were identified. The surfaces of the coatings and fracture surfaces of bulk material were investigated using atomic force microscopy (AFM). Solid state NMR revealed that samples prepared via a lactate route exhibited local Al and P environments closest to that of the melt-prepared glass, with the highest extent of Al-O-P connectivity.