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Anodizing is a high voltage electrochemical conversion process that forms barrier-type oxide layers or self-organized nanoporous/nanotubular structures. So far, alumina-like nanopores and titania-like nanotubes could be successfully synthesized on many valve metals and alloys. Recently, anodizing become possible for base metals such as polycrystalline iron and its alloys. The challenge in anodizing of iron lies in the proper control of corrosion/passivity, which can be successfully realized in organic electrolytes containing small amount of water.1-3 Anodic nanotubes and anodic nanopores may be formed on polycrystalline iron depending on electrochemical conditions adjusted in anodizing protocol. The polycrystalline iron is typically composed of the grains having the size of 2-10 µm. The kinetics of metal oxidation as well as oxygen evolution reaction, which is typically observed upon iron anodizing, may depend on the iron facet exposed to the electrolyte. In order to evaluate the dependence of the crystallographic orientation on the formed anodic film structure we investigated anodizing process on iron single crystals, namely Fe(100), Fe(110) and Fe(111). The compositional differences for porous films formed on single crystals were analyzed by means of by high resolution electron microscopy EDS elemental mapping. References: 1. H. Habazaki, Y. Konno, Y. Aoki, P. Skeldon and G. E. Thompson, Journal of Physical Chemistry C, 2010, 114, 18853-18859. 2. Y. Konno, E. Tsuji, P. Skeldon, G. E. Thompson and H. Habazaki, J. Solid State Electrochem., 2012, 16, 3887-3896. 3. K. Shahzad, D. Kowalski, C. Y. Zhu, Y. Aoki and H. Habazaki, ChemElectroChem, 2018, 5, 610-618 Figure 1 Bright field TEM micrograph for FIB cross-section of anodic film formed at 100V on polycrystalline iron in ethylene glycol electrolyte containing 1.5M H2O and 0.1M NH4F. The corresponding EDS maps show the elemental distribution of oxygen (green) and superimposed fluorine (red) and oxygen (green). Figure 1 |
