Influence of lanthanum carbonate additions on thermal stability of eutectic lithium–sodium carbonate near its melting point

Thermal behavior and stability of eutectic 52/48 Li/Na carbonate mixture containing various concentrations of lanthanum carbonate in the range 0.5–2.0 mol% was investigated by a combination of thermal analysis (DSC) and spectroscopic (EGA-FTIR) techniques under CO2 and N2 gas flows. Thermal decomposition of lanthanum carbonate with CO2 gas release was observed in the 470–480 °C range close to the melting point of eutectic alkali carbonate giving raise to formation of lanthanum oxycarbonate species. It was also found that the lanthanum carbonate phase promptly reformed, when the eutectic carbonate melt samples were cooled down to 440–460 °C under CO2 atmosphere.

► Minor additions of lanthanum carbonate strongly affected thermal stability of eutectic alkali carbonate near its melting point. ► Thermal decomposition of lanthanum carbonate occurred in the 470–480 °C range giving raise to formation of lanthanum oxycarbonate and concomitant CO2 gas release. ► Highly reversible formation of lanthanum carbonate from the corresponding oxycarbonate phase was also observed during cooling down under CO2 atmosphere. ► The freezing point of eutectic carbonate showed a linear dependence of temperature depression with the added lanthanum carbonate.