CaO and MgO Hydration at the Nanoscale: Results from Molecular Dynamics Simulations

High Resolution Image Download MS PowerPoint Slide New information about calcium oxide (CaO) hydration has been revealed by modeling aqueous crystalline CaO with the (001) and (111) surfaces on nanosecond timescales using molecular dynamics (MD) simulations with reactive force fields (ReaxFF MD). A small time step (0.1 fs) was used to ensure the correctness of the chemical reactions and time evolution. These simulations enlightened the details of the dynamics of the first reactions and the subsequent kinetics. The first calcium desorption required at least two close-distant proton absorptions, and the activation energies settled between 6–19 kJ/mol. To attain pseudo-first-order hydration kinetics, simulations over several nanoseconds have proven to be necessary. The onset and evolution of hydration were found to be statistically sensitive processes. The time evolution as well as the final phases of the hydrated surfaces depended on the initial faces. Aqueous crystalline magnesium oxide (MgO) with the (001) and (111) surfaces was also modeled, which confirmed the inert nature of highly crystalline MgO corresponding to dead-burned or fused MgO. The only water dissociation occurred at the corners of the undercoordinated oxygen atoms (CN = 3) of a crystalline MgO cube. In addition to being potentially useful in many areas, which utilize CaO hydration (steel manufacturing, construction, agriculture, chemical industry, and novel areas such as thermochemical energy storage, CO 2 capture, and hydrogen production), the results of this work can serve as a reference for initial hydration processes of other aqueous metal oxides on nanosecond timescales. The ReaxFF MD simulations on MgO provide a nanoscale contribution to the study of aqueous MgO, which can be useful, e.g., in the research of novel MgO-based binders.