Electrochemical Interpretation of Surface Dissolution Processes

Experiments were carried out using a recently developed in situ electrochemical cell in a Surface Forces Apparatus (SFA) to investigate the dissolution 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 acidic electrolyte solutions of 30 mM Ca(NO₃)₂ at 25°C. 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.