- Japan Society of Corrosion Engineering
- 防食技術 (ISSN:00109355)
- vol.31, no.3, pp.148-155, 1982-03-15 (Released:2009-10-30)
Oxidation behaviors of Fe, Co, Ni, Cu, and four Ni-Cu alloys (81, 64, 42, and 21% Ni) have been studied in 10 Torr (exceptionally, 1×10-3 Torr) of NO at the elevated temperatures from 580-780°C. The oxidation behaviors of such metals and alloys have been examined also in O2 at the same pressures and temperatures for comparison. Various methods such as microgravimetry, X-ray diffractometry, X-ray photoelectron spectroscopy, Auger electron spectroscopy, and Ion micro analysis were adopted for this investigation. The results obtained are summarized as follows: (1) The oxidation of Fe and Co in NO obeyed the cubic and the parabolic rate laws, respectively; while those of Ni and Cu obeyed the linear rate law. The oxidation characteristics (rate, rate law, or activation energy) of these metals in NO were much different from those in O2. (2) Nickel was rapidly oxidized in NO accompanied with the expansion of samples which was caused by the preferential oxidation of grain boundary. (3) The oxidation of Cu in NO was rate-determined by the dissociation of NO on the oxide surface. (4) The oxide formed on Fe, Co, Ni, and Cu in NO were Fe3O4, CoO, NiO, and Cu2O, respectively; while in O2 were Fe3O4 and Fe2O3, CoO, NiO, and Cu2O, respectively. (5) In the oxidation of Ni-Cu alloy system in NO, an accelerating oxidation was observed for Ni-rich alloys. The total amount of oxygen uptake of the Ni-rich alloy was greater than those of the Cu-rich alloys after the accelerating oxidation in NO occurred. (6) The selective oxidation characteristics for Ni-Cu alloy system during the oxidation in NO was also different from those in O2. In the former case, preferential oxidation of Ni occurred, resulting in the formation of NiO-rich oxide layer on the alloy. For the Ni-rich alloy and copper was scarcely oxidized forming only a small amount of Cu2O in the outer layer. As has generally been reported, the oxide film on Ni-Cu alloy formed in O2 consisted of two distinct layers; i. e. the component of the outer layer was copper oxide (mainly CuO) and the inner was NiO.