Acid dissolution of sodium-calcium metaphosphate glasses

The kinetics and mechanism of dissolution of (50-x)Na2O-xCaO-50P(2)O(5) metaphosphate glasses in aqueous solution at pH = 3 are reported. Kinetic data, the presence of a hydrated layer and etch pits lead to the conclusion that the dissolution at pH = 3 is limited by surface reactions. Solution analysis and surface characterization show that dissolution is congruent. Local structure and composition in the hydrated layer is identical to that in the pristine glass. After a linear period, the dissolution rate decreases, because the increase in ionic strength of the leaching solution results in a modification of the hydrated layer. (C) 1998 Elsevier Science B.V. All rights reserved.