García Rueda, F.C.; Meléndez-González, P.C.; Torres-González, J.; Antaño-López, R.; Avalos-Elizondo, L.A.; Hernández-López, J.M.: Comparative study of annealed anodic films on iron, 1018 carbon steel, and 304L stainless steel: morphological, compositional, electrochemical, and optical properties. Journal of Materials Science 60 (2025), p. 17876-17899
10.1007/s10853-025-11428-x
Abstract:
The anodizing process enables the controlled formation of ordered iron oxide structures. The electrochemical and optical properties of these materials are crucial for developing photocatalytic materials. This study compares annealed anodic films (AnAFs) produced on iron, 1018 carbon steel, and 304L stainless steel. The films were formed through anodizing in a fluoride-containing organic electrolyte with water, followed by annealing. The anodic films were analyzed using SEM–EDS, XRD, XPS, EIS, UV–Vis spectroscopy, and photoluminescence. Controlled water content in the electrolyte promoted the formation of compact oxide structures, including cubes on iron, elongated sheets on 1018 carbon steel, and dendrites on 304L stainless steel. The AnAFs displayed oxide mixtures, such as Fe2O3, Fe3O4, FeO, and FeO(OH), in all three types of AnAFs. Additionally, Cr2O3, CrO3, NiO, and Ni(OH)2 were present in the AnAFs on 304L stainless steel. Some of the best results include AnAFs with thicknesses of up to 0.41 ± 0.02 µm on iron. Low charge transfer resistances, as low as 7.73 Ωcm2, were observed for AnAFs on iron. Various band gap contributions, as low as 1.4 eV, are caused by the presence of Fe3O4 in AnAFs on iron and 1018 carbon steel. All three AnAFs can absorb visible light and exhibit n-type semiconducting behavior, while p-type behavior is exclusive to AnAFs on 304L stainless steel. This study presents a comparative analysis of the properties of AnAFs grown on iron-based substrates, demonstrating their potential for future applications, such as photocatalytic materials.