Lux-Flood Basicity of Mixed La2O3-Alkali Molten Carbonates Determined by Analysis of their Oxygen Solubility Properties

The Lux-Flood basicity of La2O3-containing alkali molten carbonate mixtures has been quantitatively estimated by a gas solubility method based on the use of acidic gaseous O2 for the titration of the oxide concentration in the melt. The amount of gaseous oxygen dissolved in the melt in form of peroxide ion has been taken as a quantitative probe for the carbonate basicity. Results demonstrate that addition of a 0.5 mol % of La2O3 to alkali carbonates is able to dramatically increase the melt basicity and that the degree of this basicity change mostly depends on the melt composition in terms of the average cation size of the alkali carbonate mixture. Plausible dissolution paths of La2O3 in molten carbonates under both acidic and basic regimes are also discussed.