Structural and thermochemical study of Na2O-ZnO-P2O5 glasses

Glasses of the (50 - x/2)Na2O-xznO-(50 - x/2)P2O5(3 <= 0/P <= 3.49) and (50 - x)Na2O-xZnO-50P(2)O(5) (O/P = 3) (0 <= x <= 33 mol%) compositions were prepared using the conventional melt quenching technique. The increase of density and glass transition temperature in both series is related to the reticulation of phosphate chains. For the first series of glasses, Fourier-transformed infrared (FTIR), Raman and P-31 solid state magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy revealed the decrease of Q(2) tetrahedral sites and the increase of phosphate dimers (Q(1)), indicating the shortening of phosphate chains. For the second series, FTIR and Raman spectroscopy show only the presence of Q2 tetrahedral sites. Dissolution of these series in 4.5% weight of H3PO4 solution has been followed calorimetrically and showed that the dissolution of the first series is endothermic for the low ZnO content and becomes exothermic when x rises. This behavior is correlated to the structural modification. For the second series, the dissolution phenomenon is endothermic confirming the presence of the same structure over the whole composition range. (c) 2014 Elsevier B.V. All rights reserved.