Iron oxidation under the influence of phosphate thin films

摘要

Iron phosphate thin films have been obtained under controlled conditions by chemical conversion deposition. The films were formed on polycrystalline α-iron by immersion in acetone, as an organic solvent. After deposition, the films were investigated by x-ray photoelectron spectroscopy (XPS) and their influence on the thermal oxidation of α-iron was studied by means of in situ low incidence x-ray diffraction of synchrotron radiation. The study reveals interesting features related to the structure of both the phosphate and thermal oxide films. The XPS data suggest the iron phosphate to be constituted of long chains of phosphate groups PO_(4)~(3-); these groups being interconnected by Fe~(2+) and Fe~(3+) cations. X-ray diffraction measurements have shown a significant modification of the oxidation behavior of α-iron at 400℃ and atmospheric pressure, which is derived from the presence of the thin film: α-Fe_(2)O_(3) formation is clearly enhanced to the detriment of Fe_(3)O_(4), compared to the oxidation of pure iron in which Fe_(3)O_(4) is the dominant phase. As the growth rate of the α-Fe_(2)O_(3) layer is significantly reduced compared to that of Fe_(3)O_(4), thus the phosphated layers may find niche applications in low-to-moderate temperature environments.