Molecular Dynamics Modeling of Chloride Binding to the Surfaces of Calcium Hydroxide, Hydrated Calcium Aluminate, and Calcium Silicate Phases

Molecular dynamics computer simulations are performed to study the structure and dynamical behavior of chloride and associated cations at the interfaces between aqueous solutions and portlandite (Ca(OH)2), Friedel's salt ([Ca2Al(OH)6]Cl·2H2O), tobermorite (Ca5Si6O16(OH)2), and ettringite (Ca6[Al(OH)6]2[SO4]3·26H2O). These phases are important in calcium silicate and calcium aluminate cements and are models of important poorly crystalline cement phases. They are also representative of many hydrous hydroxide, aluminate, and silicate materials stable near room temperature and pressure. The MD simulations use a recently developed semiempirical force field and take into account the flexibility of surface OH groups and allow for energy and momentum transfer between the solid and solution to effectively simulate the sorption. The principal focus is on the structure at and near the solution/solid interfaces and on the molecular mechanisms of adsorption of aqueous Cl-, Na+, and Cs+ ions on a neutral portlandite su...