Mitigation of tribocorrosion of metals in aqueous solutions by potential-enhanced adsorption of surfactants.

Abstract

Corrosion and corrosive wear occur commonly on metals surface in aqueous solutions. External electric field is usually considered as one of the factors to accelerate corrosion or corrosive wear of materials in the presence of conventional electrolytes. This work aims to reposition widely believed perspective by experimental justification which have been conducted in aqueous solutions containing surfactants. Electric potential of metal surfaces was modulated externally within the electrochemical potential window of the metal electrode-solution-counter electrode system, which actively regulated the adsorption or desorption of surfactant molecule in the aqueous solution over the electrodes to form a molecular barrier of electron transportation across the electrode-electrolyte interface. The advantage of the approach over the anodic passivation is negligible redox reactions on the protected electrode surface while a better lubricious and wear resistant film than oxide is maintained in the meantime. Tribopairs of several metal/metal and metal/ceramic were tested by employing a ball-on-disc tribometer with anionic and cationic surfactants solutions. For anionic surfactant as the modifier, positive surface potential enables coefficient of friction to be decreased by promoting the formation of adsorption film on metal surface in aqueous solutions. For cationic surfactant, negative surface potential plays a role in decreasing the coefficient of friction. Phase diagrams of friction and wear in wide ranges of surfactant concentration and surface potential were plotted for the tested metal/metal and metal/ceramic tribopairs. These results indicate that the adsorption behavior of molecules or ions at the metal-aqueous interface can be well regulated when an external electric field is present without inducing corrosion or corrosive wear.