Deep-UV Raman spectroscopic analysis of structure and dissolution rates of silica-rich sodium borosilicate glasses

Abstract

As part of ongoing studies to evaluate relationships between structure and rates of dissolution of silicate glasses in aqueous media, sodium borosilicate glasses of composition Na 2O·xB 2O 3·(3 − x)SiO 2, with x ≤ 1 (Na 2O/B 2O 3 ratio ≥ 1), were analyzed using deep-UV Raman spectroscopy. Results were quantified in terms of the fraction of SiO 4 tetrahedra with one non-bridging oxygen (Q 3) and then correlated with Na 2O and B 2O 3 content. The Q 3 fraction was found to increase with increasing Na 2O content, in agreement with studies on related glasses, and, as long as the value of x was not too high, this contributed to higher rates of dissolution in single pass flow-through testing. In contrast, dissolution rates were less strongly determined by the Q 3 fraction when the value of x was near unity, and appeared to grow larger upon further reduction of the Q 3 fraction. Results were interpreted to indicate the increasingly important role of network hydrolysis in the glass dissolution mechanism as the BO 4 tetrahedron replaces the Q 3 unit as the charge-compensating structure for Na + ions. Finally, the use of deep-UV Raman spectroscopy was found to be advantageous in studying finely powdered glasses in cases where visible Raman spectroscopy suffered from weak Raman scattering and fluorescence interference.