Location of Artinite (Mg₂CO₃(OH)₂·3H₂O) within the MgO-CO₂-H₂O system using ab initio thermodynamics

The MgO-CO₂-H₂O system have a variety of important industrial applications including in catalysis, immobilisation of radionuclides and heavy metals, construction, and mineralisation and permanent storage of anthropogenic CO₂. Here, we develop a computational approach to generate phase stability plots for the MgO-CO₂-H₂O system that do not rely on traditional experimental corrections for the solid phases. We compare the predictions made by several dispersion-corrected density-functional theory schemes, and we include the temperature-dependent Gibbs free energy through the quasi-harmonic approximation. We locate the Artinite phase (Mg₂CO₃(OH)₂·3H₂O) within the MgO-CO₂-H₂O phase stability plot, and we demonstrate that this widely-overlooked hydrated and carbonated phase is metastable and can be stabilised by inhibiting the formation of fully-carbonated stable phases. Similar considerations may apply more broadly to other lesser known phases. These findings provide new insight to explain conflicting results from experimental studies, and demonstrate how this phase can potentially be stabilised by optimising the synthesis conditions.