Dissolution behaviour of sodium calcium polyphosphate glasses

A series of xNa₂O–xCaO–(100–2x)P₂O₅ (NCP, 24≤x≤31, 3·0≤(O/P)≤3·5) polyphosphate glasses were reacted in deionized water for different times and temperatures. Dissolution rates were determined from weight loss measurements and from the concentrations of ions released to the water. These Na,Ca-phosphate glasses dissolve congruently, with the relative concentrations of ions in solution the same as those in the original glasses. Glass dissolution occurred in two stages, the first described by a square root time dependence and the second by a linear time dependence. The dissolution rate constants for both stages decrease by an order of magnitude as the O/P ratio of the glasses increased. The activation energies associated with these rate constants also decreased, from 83±5 to 24±4 kJ/mol, with an increase in the O/P ratio.