Abstract
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(102 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 O2 reduction by increased O2 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.
Highlights
The fact that light affects electrochemical reactions is known for almost 2 centuries [1]
Iron was immersed in 0.1 M HCl, 0.2 M NaOH and 3.5 wt% NaCl, while Ecorr was recorded vs. a saturated calomel electrode (SCE) that was connected to the iron through a salt-bridge
A convective mechanism is identified as the dominating mechanism that leads to enhanced dissolution under the conditions used in this work
Summary
The fact that light affects electrochemical reactions is known for almost 2 centuries [1]. Titanium, zirconium and 304 stainless steel showed no effect from illumination while brass corroded slower when irradiated [2]. This effect was attributed to electron-hole pair formation in the metal oxide in a semiconductor photoelectrochemistry mechanism [2]. One result showed a corrosion rate up to 9× higher when illuminated with UV compared to dark Such an observation was postulated to be the result of formation of reactive oxygen radicals by holes generated through the interaction of light with iron oxide [4]. Erbe typically used to explain Ecorr developing spontaneously on a submerged metal
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