In-situ characterization of borate glass dissolution kinetics by μ-Raman spectroscopy

The dissolution behavior of binary and ternary Na-Ca-borate glasses in phosphate-containing aqueous solutions was studied by micro-Raman spectroscopy. Raman spectra collected from the solutions provided information about the types and concentrations of borate anions released from the glass as a function of time. Boric acid molecules (H3BO3) and tetrahydroxyl borate anions (B(OH)4−) can be detected in solution and their relative concentrations depend on the solution pH. By monitoring the areas under peaks associated with these two species, the overall borate release rates and variations in solution pH were determined. Binary Na-borate glasses exhibit linear dissolution kinetics and the dissolution rates decrease with Na2O-contents up to 30 mol%. The ternary Na-Ca-borate glasses exhibit parabolic dissolution kinetics because of the formation of a surface Ca-phosphate phase, and these reaction rates also decrease with increasing [Na2O + CaO] content.