Effect of aqueous Mg2+ and Ca2+ cations on the dissolution kinetics and alteration layer of sodium borosilicate glasses at neutral pH buffered with Tris/HCI

摘要

Two sodium borosilicate glasses have been altered in solutions containing either MgCl2 or CaCl2(4x10(-2) M), at neutral pH using Tris/HCl as a buffer. The two glasses have different dissolution rates due to their different B/Si contents. The dissolution kinetics have been measured by solution analysis, and the alteration layers have been characterized at different stages of the alteration by TOF-SIMS, SEM-EDX and ATR-IR spectroscopy. The cations present in the aqueous solution have an important and distinct influence on the dissolution kinetics and on the microstructure of the alteration layer, although they are not fixed into the layer at this pH. The CaCl2-bearing solution buffered with Tris/HCl strongly destabilizes the glass interface and induces a congruent dissolution of the glass and precipitation of silica from the solution. The MgCl2-bearing solution buffered with Tris/HCl does not show such a dramatic effect; it decreases the Si release rate at short times but, at long times, it limits the dissolution rate drop. The Mg2+ cations modify the evolution of the porosity microstructure of the alteration layer.