High pressure effect on the short- and intermediate-range structure of depolymerized soda lime silicate glass: Insights from micro-Raman spectroscopy

Abstract

The network structure pressure dependence of a modified soda lime silicate glass, containing CaF2 and lower SiO2 content, was investigated by micro-Raman spectroscopy. The glass structure was first analyzed under normal pressure conditions in terms of network depolymerization, by comparing with commercial soda lime glass. Using calculation of non-bridging oxygens per tetrahedron (NBO/T), it was found that while commercial soda lime glasses have Q4 and Q3 units, the studied glass system presents a depolymerized structure and it is composed, on average, of Qn with n = 3 and 2. Changes due to high hydrostatic pressure were evaluated by using a diamond anvil cell up to 19 GPa. Raman scattering was used to calculate Si–O–Si angular population according to the network central force, which showed a progressive angle closure with pressure. The Raman spectrum of recovered sample, after compression/decompression cycle, showed negligible changes, suggesting that initial amorphous phase of modified glass is highly stable. The glass showed very high incompressibility, compared to aluminates, silicates, lanthanum borogermanate, or even regular soda lime glasses, suggesting that its bulk modulus is relative high. Polymerized glasses have great space vacancies within the network structure, on the contrary it was observed that the studied glass presents a densely packed structure reflecting on high incompressibility, which decreased the magnitude of permanent densification.