The kinetics and mechanism of MgO dissolution

Reactions and atomic rearrangements at fluid-crystal interfaces play an imp ortant role in catalysis and in controlling the kinetics and mechanisms of dissolution. We have studied the attachment and reactions of water molecule s at the MgO-water interface by combining measurements of H-1 and D-2 surfa ce penetration and etch pit morphology with ab initio calculations. These s tudies show that the most common MgO cleavage surface, (001), is thermodyna mically unstable when hydrated. Proton rearrangement on such surfaces prece des proton-cation exchange and provides a general mechanism for the detachm ent of ions during dissolution. The kinetics of dissolution are strongly in fluenced by the concentration of surface defects and a simple model based o n 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. (C) 1999 Elsevier S cience B.V. All rights reserved.