Carbonate-Induced Structural Transformation of Lithium–Sodium Orthoborate to a Low-Viscosity Metaborate via CO₂ Capture

This paper reports on the structural changes occurring within the lithium–sodium orthoborate crystal lattice during the solid-state absorption of CO 2 . Results derived from Fourier transform infrared measurements indicate that the CO 2 -saturated mixed-alkali metal orthoborate and its CO 2 -lean metaborate counterpart essentially present the same spectral profile, suggesting that CO 2 capture results in a fundamental shift of the orthoborate composition to the metaborate one. The implications of such a structural transformation were examined in the molten state at elevated temperatures through rheological measurements, and although confirming that the CO 2 -lean metaborate exhibits a higher viscosity than the CO 2 -lean orthoborate, the results suggest that incorporation of CO 2 in the orthoborate ionic lattice dilutes the melt, leading to a remarkable reduction in its overall viscosity, despite causing a structural transformation from the less viscous orthoborate form to the more viscous metaborate one.