Enhanced Corrosion Mitigation of TiO2 coated Stainless Steels Under UV Illumination

Abstract

Austenitic stainless steels are commonly used as the structural material for dry-storage canisters in nuclear power plants because of their excellent corrosion resistance and mechanical properties. Dry-storage canisters are often exposed to chloride containing atmosphere near seashores, which could induce localised stress corrosion cracking in these stainless steels near the welded regions. TiO2 coatings applied on stainless steel substrates (i.e. Type 304 stainless steels) along with ultraviolet (UV) irradiation have been proposed as a mitigation measures against the corrosion in canister materials. In this study, TiO2 coatings were applied on stainless steel samples using a sol-gel dip-coating method. The corrosion characteristics of the coated samples were studied under the conditions of different coating treatments, annealing temperatures, annealing atmospheres and UV illumination durations. The corrosion mitigation performance of the coated samples with and without UV illumination was evaluated by electrochemical polarization analyses and open-circuit potential measurements. The surface morphologies of the samples were studied by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and laser Raman spectroscopy. In addition, the photocatalytic responses of these coatings exposed to various acidic and alkaline aqueous solutions under aerated and deaerated conditions were also studied. The results indicated that the TiO2 coating not only could lead to low electrochemical potentials of the stainless steel samples during UV illumination, but could also maintain the low electrochemical potentials even after the cut off of UV illumination. Results from Electrochemical polarization analyses further support the superior corrosion resistance under UV-illumination conditions. Keywords: Stainless steel, TiO2 coating, ultraviolet illumination.