Towards the reconciliation of viscosity change and CO2-induced polymerization in silicate melts

Glass transition temperature (Tg) measurements show that increasing CO2 content induces a decrease in Tg implying a decrease in viscosity for the studied low silica melt composition. This result appears in complete contradiction with the melt polymerization induced by CO2 as quantified by NMR. We propose a model that reconciles both aspects. CO2 induces silicate subnetwork polymerization resulting in a viscosity increase but it also induces a competing effect by forming a carbonate subnetwork having a low viscosity. The overall result appears dominated by the carbonate subnetwork resulting in a slight decrease in melt viscosity in agreement with existing studies.