Electrostatic Origin of Enhanced Rate of Silica Surface Dissolution

Using an electrochemical cell in a Surface Forces Apparatus (EC-SFA) we found an enhanced dissolution rate of silica surfaces in close proximity to either muscovite mica or a gold surface as functions of time and electrochemical potential. The surfaces was pressed together at relatively low pressures (a few atm) while submerged in weak electrolyte solutions at 25°C and over a wide range of pH. Typical dissolution rates varies from 0.1 – 4 Å/ min, depending on the “effective” potential difference Δψ. For the silica-mica interface the origin of the Δψ is interpreted as arising from the overlapping of the double layers of the surfaces. The Δψ of the gold surface was controlled by a potentiostat. We find that changes in the dissolution rates of silica correlate quantitatively with the Δψ via a Butler-Volmer type equation, suggesting the dissolution is driven, at least in part, by electrochemical reactions. Our finding may have implications for a wide variety of applications, from geological processes to chemical mechanical polishing.