偏光解析法による鉄表面不働態皮膜の研究
1973 年 37 巻 9 号 p. 951-957
詳細
1973 年 37 巻 9 号 p. 951-957
The anodic passivation film formed on iron in neutral borate-buffer solution has been studied by using ellipsometric, electrochemical, and gravimetrical techniques. The film can be dissolved from its outer surface by applying a cathodic current in borate-buffer solution at pH 6.35 in which the reductive dissolution,
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oindentproceeds at 100 per cent current efficiency. Ellipsometric measurements carried out during the galvanostatic-cathodic reduction of the film in this solution reveals that the film consists of two layers, an inner layer with the optical constant 3.0−0.5i and an outer layer with the constant 1.8−0.1i. It is also shown that the density of the inner layer is in agreement with that of γ-Fe2O3.
The inner layer thickness increases linearly with the passivating potential, and the potential extrapolated at zero thickness of the inner layer corresponds to the equilibrium potential of the anodic formation of γ-Fe2O3,
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oindentThe outer layer, however, is not directly related to the anode potential.
Thermo-gravimetrical measurements indicate that the film contains some amount of water which is concentrated in the outer layer. The average composition of the outer layer is estimated as Fe(OH)3.
A film model is proposed in which the inner layer of anhydrous γ-Fe2O3 is the cause of the potential drop in the film producing a field intensity of 5.6×106 V/cm and the outer layer of hydrous ferric oxide depends on the solution environment and passivation process.
