金属表面における薄いアノード酸化皮膜成長過程の速度論的研究方法に対する寄与―ニッケル不働態皮膜成長の速度論

抄録

Three different methods, the galvanostatic, the potentiostatic and the rapid can be used to measure the rate of growth of the anodic oxide film on metals. By using these methods, the rate of growth of a passive oxide film on nickel was measured in ln H₂SO₄ at 40°C. The rate of growth i can be expressed in the form i=i₀exp(β′ε), where β′=zaeα⁄kT and ε is the strength of the electric field which can be expressed as ΔE⁄d. The value of β′=40×10⁻³ coul./V·cm² obtained by the galvanostatic method was considerably different from β′=416×10⁻³ coul./V·cm² obtained by the rapid method. Under a certain potentiostatic condition, the value of β′ was almost equal to that measured by the galvanostatic method except in the initial period immediately after the change of the potential when β′ is larger than 250×10⁻³ coul/V·cm² and rather close to the β′ obtained by the rapid method. From these results, it may be presumed that the significance of the measured values are essentially different in the galvanostatic method and in the rapid method. From the β′ of the galvanostatic method, the plausible value of a≈2.3 Å, as the thickness of the energy-barrier in the rate-process, was obtained under the assumption of α=0.5.