Solid state NMR study of phosphosilicate gels

Solid state 29Si, 31P and 1H MAS-NMR were used to investigate structural aspects of gel-derived glasses of molar composition 10P2O5 · 90SiO2 (10P) and 30P2O5 · 70SiO2 (30P). 31P MAS-NMR spectra of the 10P and 30P gels dried at 100 °C show resonances characteristic of orthophosphoric and pyrophosphoric acid. No evidence for cross-linking with silicate matrix was found by 29Si NMR at this temperature while 1H MAS-NMR experiments suggest that the chemical environment of OH groups is very similar in these samples. In spite of this initial similarity further heating causes markedly different structural rearrangements of the 10P and 30P gel matrix.