Content area
Abstract
The structure of alkali silicate glasses and melts is investigated using a multi-spectroscopic approach. Raman spectroscopy is used to characterize the local to intermediate range order within the glasses. We show that the distribution of rings varies as a function of composition, with 3-membered rings gaining importance with increasing alkali content. We apply a newly developed model for the tting of the high frequency envelope related to SiO4 symmetric stretch vibrations of Qn species. These ts are interpreted using the idea of modifier bound bridging oxygen. The proportions of the different Qn species vary with alkali concentration with Q4 species breaking down to form lower order Qn species with increasing alkali content. The Q2 peak appears at increasingly higher concentrations of M2O with increasing cation size. This leads us to believe that cations with a higher charge density cluster more readily than cations with a lower charge density. At the 20 mol. % composition we see a change in the silicate network, as shown by the absence of a Q4 peak and the proportion of 3-membered rings.
The unique behaviour of lithium was investigated using X-ray absorption near-edge structure spectroscopy. We conducted experiments on a variety of lithium-bearing salts, minerals and glasses (LS: lithium silicate and LMS: lithium alkaline-earth silicate glasses) in order to characterize the lithium bonding environment. The Li K-edge position depends on the electronegativity of the element to which it is bound. The intensity of the first peak varies, depending on the existence of a 2p electron and can be used to evaluate the degree of ionicity of the bond. Crystalline lithium metasilicate has a sharp, strong intensity absorption edge whereas the lithium silicate glasses all have a weak intensity edge feature, similar to that of lithium carbonate. The area of the absorption edge peak increases with the lithium content of the LS glasses. The LMS glasses edge peak changes drastically depending on the alkaline-earth present. The peak area of the LMS glasses decreases with increasing charge density from barium to magnesium. We believe that the presence of Mg leads to more covalent-like Li-O bonds.
