Effects of anodizing conditions and annealing temperature on the morphology and crystalline structure of anodic oxide layers grown on iron

• Published in: Applied surface science 2017-12, Vol.426, p.1084-1093
• Main Authors: Pawlik, Anna, Hnida, Katarzyna, Socha, Robert P., Wiercigroch, Ewelina, Małek, Kamilla, Sulka, Grzegorz D.
• Format: Article
• Language: English
• Subjects: Annealing; Anodization; Hematite; Iron oxides; Magnetic field; Magnetite
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2017.07.156

[Display omitted] •Anodization of Fe in an ethylene glycol-based solution containing fluoride ions and water was performed.•Effect of the anodizing temperature on the morphology of anodic nanoporous layers on iron was investigated.•Effects of electrolyte stirring rate and magnetic field on the structure of nanoporous layers on iron were studied.•Phase transition in an anodic layer was analyzed by XRD, XPS, and Raman spectra. Anodic iron oxide layers were formed by anodization of the iron foil in an ethylene glycol-based electrolyte containing 0.2M NH4F and 0.5M H2O at 40V for 1h. The anodizing conditions such as electrolyte composition and applied potential were optimized. In order to examine the influence of electrolyte stirring and applied magnetic field, the anodic samples were prepared under the dynamic and static conditions in the presence or absence of magnetic field. It was shown that ordered iron oxide nanopore arrays could be obtained at lower anodizing temperatures (10 and 20°C) at the static conditions without the magnetic field or at the dynamic conditions with the applied magnetic field. Since the as-prepared anodic layers are amorphous in nature, the samples were annealed in air at different temperatures (200–500°C) for a fixed duration of time (1h). The morphology and crystal phases developed after anodization and subsequent annealing were characterized using field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The results proved that the annealing process transforms the amorphous layer into magnetite and hematite phases. In addition, the heat treatment results in a substantial decrease in the fluorine content and increase in the oxygen content.