Convection induced by illumination-based metal surface heating increases corrosion potential, corrosion rates.

Illumination may increase corrosion rates of important engineering metals. In addition to the well-known photoelectrochemical mechanism which increases dissolution via generation of electron-hole pairs, induced convection via local heating can contribute to increased dissolution. Here, corrosion potential shifts of iron in HCl, aqueous NaCl and NaOH upon illumination with O (1 0 2 W cm−2) white light have been found to be O (10 mV), accompanied by increased corrosion rates. The increase in corrosion potential can be suppressed by stirring. These results are interpreted in the framework of the mixed potential theory. An increase in the diffusion limited current of the O 2 reduction by increased O 2 transport to the surface via induced convection leads to increased corrosion potentials, and thus increased corrosion rates. The induced convection mechanism of increased photocorrosion can be recognised by a delayed onset of corrosion potential shifts. In practice, this mechanism is anticipated to be important mainly in thin film electrolytes under strong illumination. Unlabelled Image • Illumination of a metal leads to heating of the metal surface. • The resulting temperature gradient increases the natural convection velocity. • Increased natural convection increases oxygen transport to the surface. • Increased oxygen transport leads to increased corrosion rates. • Stirring or enforcing convection suppresses the effect. [ABSTRACT FROM AUTHOR]