MICROSTRUCTURE DEVELOPMENT OF Li₂CO₃-CaCO₃ EUTECTIC MIXTURE IN CO₂ (g) AND N₂ (g) ENVIRONMENTS

Résumé
On a étudié la formation des microstructures de Li₂CO₃, de CaCO₃ et de mélanges eutectiques Li₂CO₃-CaCO₃ sous CO₂(g) et N₂(g) à 800 K. A cette température CO₂(g) favorise le frittage de CaCO₃ et limite la croissance des crystallites de Li₂CO₃. Au dessus de la température eutectique (935 K) ces phénomènes s'observent aussi dans le mélange eutectique.

Abstract
Reaction between CaO powdevs and CO₂(g) is often limited by the slow diffusion of CO₂ through the CaCO₃ product. Addition of Li₂CO₃ has been proved effective in modifying the CaCO₃ layer, up and below the eutectic temperature (935 K). This study deals with the microstructure development of Li₂CO₃, CaCO₃ and Li₂CO₃-CaCO₃ eutectic mixture in CO₂(g) and N₂(g) at 800 K. At this temperature CO₂(g) enhances the sintering of CaCO₃ and reduces the grain growth of Li₂CO₃ crystallites. At temperatures below the eutectic one these features have been observed also within the eutectic mixture. Accordingly, the protective layer of CaCO₃ formed in the CaO carbonatation has a more open microstructure, and the reaction rate between CaO and CO₂ is increased.