Quantum chemical study of thermal decomposition mechanism and polymorph predict phase transitions of magnesite

Abstract

A detailed quantum chemical study was performed by Gaussian 03 at the MP2(full)/6-311++G(d,p) level to explore the thermal decomposition mechanism of magnesite. The four microscopic reaction pathways and the intermediates in the thermal decomposition process are located by energy barriers. The rate constants of the four reaction pathways are evaluated by the conventional transition-state theory (TST) over a temperature range of 298–1,100 K. Comparing with the experimental rate constants, it was found that path A (R(MgCO3) → IM0 → P(MgO + CO2)) is the most favorable pathway. The polymorph predict results indicate that magnesite undergoes directly structural phase transition from the rhombohedral structure ( $$ R\bar{3}c $$ ) to the chiral orthorhombic structure (Pna21) during the thermal decomposition process of magnesite.