Designing micro-nano structure of anodized iron oxide films by metallographic adjustment on T8 steel

In this study, the anodized iron oxide films with micro-nano structure were prepared by a combination of heat treatment and anodization. The adjustment of these oxide films at the micron-scale was achieved by heat treatment on substrate to modify the position of the cementite and ferrite. The distribution and existing forms of carbon on cementite and ferrite determine the morphology of their respective anodization. It was found annealing at 300 °C can improve the crystallinity of iron oxide and maintain the original micro-nano structure. Although the crystal quality of iron oxide can be further improved with higher annealing temperature, it would result in the collapse of nanoporous structures and the reconstruction of the surface morphology. Furthermore, anodized samples made from those with lamellar ferrite and cementite show better specific capacitance. The iron oxide film on the annealed substrate obtained the highest specific capacitance of 35.3 mF/cm² at a scan rate of 20 mV/s in our samples.