Carbonate speciation in depolymerized and polymerized (alumino)silicate glasses: Constraints from 13C MAS and static NMR measurements and ab initio calculations

Our 13C MAS and static NMR data, as well as infrared spectroscopic data (moderate Δν3 of 60-100 cm−1) from the literature, for depolymerized silicate and aluminosilicate glasses are all indicative of free carbonates as the dominant species. Data for nominally fully polymerized aluminosilicate compositions, on the other hand, are consistent with carbonate groups bonded to two Si/Al via two oxygens (network carbonate) as the dominant species. The quantitative 13C MAS NMR data also revealed the coexistence of a small amount of the other type of carbonate species, especially for Ca aluminosilicate glasses. These new structural insights should be valuable in helping better understand physical properties (e.g. viscosity) of CO2-bearing silicate melts of diverse compositions.