Abstract
The mechanism behind corrosion rate increase of anodised iron under illumination has been studied by comparing photocurrents with corrosion currents from polarisation curves under controlled convection. Under illumination with photon energies larger than the iron oxide band gap of ∼2 eV, corrosion current densities increased by maximum 30%, triggered largely by hole annihilation through cation dissolution. Thermal effects in the oxide also play a role. Photocurrent measurements indicate little upward band bending, with fluctuations, in the n-type oxide at open circuit. The contributions of different mechanisms to the photocorrosion rate have been quantified, relevant for steels and photoelectrochemical water splitting.
Highlights
An increase of corrosion rates with illumination was observed already more than a century ago for iron in alkaline electrolytes [1,2]
Anodisation was chosen as a low-temperature preparation technique over thermal or gas phase deposition techniques as the results are perceived to be closer to corrosion products from aqueous solutions; differences between thermally and electrochemically grown oxide films have been reported [34]
Anodisation was conducted by potentiostatic polarisation with a DC N5771A power supply, for up to 10 min at either 1.5, 2.0 or 3.0 V, using a titanium plate 5× the surface area of the iron as cathode
Summary
An increase of corrosion rates with illumination was observed already more than a century ago for iron in alkaline electrolytes [1,2]. The photoactivity of the iron corrosion products was recognised, via their semiconducting properties [4,5]. Increased corrosion rates under illumination were related to the photoactivation of semi conducting oxide corrosion products [6,7]. UV irradiation for up to 6 months has shown to increase weight loss for some metals like zinc, carbon steel, aluminium, copper and silver when immersed in running water [8]. No effect or a decreased weight loss compared to the control was found for titanium, aluminium, nickel and 304 stainless steel. The Gerischer model for charge transfer at semiconductor electrodes was adapted and it was postulated — without experimental evidence to that end — that the holes from electron–holes pairs created during illumination annihilated via disso lution of the metal oxide [8]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
