In the previous report it was supposed that steel portion in sea water acted as cathode of macro-corrosion cell, but as a result of further investigation it was confirmed that, at steel sheet piles on sea side, the steel portion above mean low water level served as cathode while that under mean low water level as anode. Moreover, the three kinds of corrosion tendencies of steel sheet piles, which were reported previously, depended considerably on the existence of tidal range, the depth of water, the presence of fresh water, and so on, as follows:
Corrosion tendency (a) was likely to be generated when water level changed every 6 hours and the ratio of cathodic area to anodic area of steel, A_c/A_a, was 0.1 or more and the specific resistance of water, ρ, was greater than 25Ω-cm, especially in the range of several hundreds to a thousand Ω-cm.
Corrosion tendency (b) was likely to be generated when there was tidal level difference and A_c/A_a was 0.1 or more and ρ was nearly equal to 25Ω-cm.
Corrosion tendency (c) was likely to be generated when water level changed every 6 hours and A_c/A_a was 0.1 or less and ρ was nearly equal to 25Ω-cm or when there wasn't daily tidal change.
As mentioned above, it is supposed that corrosion tendencies of steel sheet piles can be explained from the point of view of macro-corrosion.

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The coercive force of the oxides, prepared by the air-oxidation of ferrous hydroxide colloid doped with copper (II) of various Cu/Fe ratios (0-6.5%), was examined to clarify the effect of copper. The oxides which develop in the particle size by the effect of copper, in a limited range (1-3%) of copper content, showed lower coercive force in comparison with the oxides of smaller particle sizes. The variation of the secondary structure of the oxidation products from Fe(OH)₂ colloids containing Cu in the above mentioned range, extensively demonstrated in the preceding report, was thus inferred to the theory that the oxide particles with lower magnetization can form densely packed secondary particle agglomerates.
The degree of SO₂ (1% in oxygen) oxidation by the similar series of oxides of different Cu/Fe ratios was compared to show that the oxides with low coercive force result in the low activity to the SO₂ oxidation, presumably by a magneto-catalytic effect.
These experimental results may contribute to explain the anti-corrosive effect of copper added to steel.

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