Decomposition of Li₂CO₃ by Interaction with SiO₂ in Mold Flux of Steel Continuous Casting

Abstract

The effect of SiO₂ addition on the decomposition of Li₂CO₃ was investigated using the thermo-gravimetric and differential scanning calorimetric method (TG-DSC) at temperatures up to 1000°C. Addition of SiO₂ greatly enhanced the decomposition of Li₂CO₃. The main decomposition reaction began to take place around 600°C, and completed just above the melting point of Li₂CO₃. The decomposition product was Li₂O · SiO₂ irrespective of the Li₂CO₃ to SiO₂ mixing ratio as long as both reactants were available. It was ascertained that a liquid layer between Li₂CO₃ and SiO₂ particles formed and facilitated the decomposition reaction. The governing reaction of the decomposition was the reaction between the dissolved Li₂CO₃ and SiO₂ in the liquid layer to form Li₂O · SiO₂. The decomposition rate was independent of the Li₂CO₃/SiO₂ mixing ratio until either one had been completely exhausted. When excess Li₂CO₃ existed, it further reacted with the initial product of Li₂O · SiO₂ to form 2Li₂O · SiO₂. When SiO₂ was found in excess, on the other hand, no further reaction took place. This is attributed to the fact that upon Li₂CO₃ exhaustion there is no liquid phase available to facilitate further reaction. The apparent activation energy of the decomposition of Li₂CO₃ in existence with SiO₂ is 198 kJ mol⁻¹.