The kinetics and mechanism of MgO dissolution

Reactions and atomic rearrangements at fluid-crystal interfaces play an important role in catalysis and in controlling the kinetics and mechanisms of dissolution. We have studied the attachment and reactions of water molecules at the MgO-water interface by combining measurements of ¹H and ²D surface penetration and etch pit morphology with ab initio calculations. These studies show that the most common MgO cleavage surface, (001), is thermodynamically unstable when hydrated. Proton rearrangement on such surfaces precedes proton-cation exchange and provides a general mechanism for the detachment of ions during dissolution. The kinetics of dissolution are strongly influenced by the concentration of surface defects and a simple model based on the ab initio results predicts a dissolution rate of 10^-10 mol cm^-2 s^-1 for a typical surface defect concentration of 0.1.