Structural investigations and calorimetric dissolution of manganese phosphate glasses
Résumé
Two series of manganese phosphate glasses (50x/2)Na2O-xMnO-(50 − x/2)P2O5 and (50 − x)Na2O-xMnO-50P2O5 (0 ≤ x ≤ 33 mol%), were prepared and investigated by means of density measurements, molar volume evolutions, FTIR and Raman spectroscopy, differential scanning calorimetry and calorimetric dissolution. In both series, density and glass transition temperature increase with composition. For the first series of glasses (3 ≤ O/P ≤ 3.49), spectroscopic analysis indicates that the addition of MnO content induces an evolution of structural units from Q2 to Q1 tetrahedral sites indicating the depolymerization of phosphate chains. By introducing MnO oxide into the second glass series (O/P = 3), Psingle bondOsingle bondP linkages are disrupted, suggesting a structural changes in the vitreous network. Calorimetric dissolution of both series of glasses in 4.5% weight of H3PO4 solution shows that the dissolution phenomenon is endothermic for the low MnO content and becomes exothermic as MnO concentration increases. This behavior may be correlated to the structural modification resulted from the depolymerization of the infinite metaphosphate chains.