Dissolution of (50-x)Na_2O-xCaO-50p_2O_5 metaphosphate glasses in different saline solutions: mechanism and kinetic control

摘要

The dissolution of (50-x)Na_2O-xCaO-50P_2O_5 metaphosphate glasses has been investigated at pH 3 in solutions containing in Na~+, Ca~(2+), Cl~-, NO_3~- and (PO_3~-)_n ions. Whatever the conditions, a hydrated layer develops over a surface covered with each pits. Na~+ and Cl~- have no specific effect on the dissolution kinetics and mechanism. In Ca~(2+)-containing solutions, XPS, electrophoretic mobility and ~31P NMR show that Na~+ is exchanged for Ca~(2+) in the hydrated layer, resulting in a decreased dissolution rate. Polyphosphate anions, (PO_3~-)_n, act as complexing agent for Ca~(2+), and counterbalance its inhibiting effect on the dissolution rate.