Analysis of chemical reaction between Li₄SiO₄ and CO₂ by thermogravimetry under various CO₂ partial pressures—Clarification of CO₂ partial pressure and temperature region of CO₂ absorption or desorption

Chemical reaction between CO₂ and Li₄SiO₄ was investigated using thermogravimetry under various P(CO₂). Under P(CO₂) of 1.0 bar, weight increase originating from CO₂ absorption reaction was observed from ∼500 °C and abrupt weight reduction due to CO₂ desorption was detected at ∼700 °C. With decreasing P(CO₂), the latter temperature decreased. Since fair agreement was observed between the latter temperatures and thermodynamically calculated equilibrium temperatures of Li₄SiO₄ + CO₂ ↔ Li₂CO₃ + Li₂SiO₃, the latter temperatures could be regarded as approximate equilibrium. Dependence of the calculated equilibrium temperatures and approximate equilibrium temperatures on P(CO₂) was represented with Ellingham diagram, showing P(CO₂) and temperature region of CO₂ absorption or desorption. Approximate equilibrium temperature under P(CO₂) of 1.0 bar agreed with the calculation, whereas deviation was observed under low P(CO₂), resulted in larger apparent ΔS° and ΔH° than the calculated ones. Using specimen with smaller particle size, the deviation reduced due to enhancement of CO₂ desorption kinetics.