This experiment was conducted for the purpose of clarifying the effects of impurity elements on the corrosion resistance of commercially pure titanium. The ranges of impurity elements studied were <0.01-0.49% for Fe, 0.042-0.291% for O, 0.011-0.026% for Si, 0.0012-0.028% for C and 0.0012-0.059% for N.
In the oxidizing solution, boiling 65% HNO₃, any impurity element has no effect on the corrosion rate. In the non-oxidizing acid solutions where titanium is actively corroded, the corrosion rates are increased by the presence of more than 0.15% Fe in the boiling 1% H₂SO₄ and 0.03% Fe in the boiling 5% HCl, while the presence of Si, C, and N decrease the corrosion rates slightly and O has no effect. When titanium is subjected to the heat cycle simulated to that of heat affected zone in welding, the presence of more than 0.05% Fe increases the corrosion rate in the boiling 1% H₂SO₄ solution, whereas Fe exerts no effect in the oxidizing solution.

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Tie rod is the steel bar which is used to prevent steel sheet pile structures from destruction and fox convenience placed in sandy layer at tidal zone. Accordingly, tie rod is connected with steel in saturated sandy layer, that is, steel sheet pile below residual water level, and contacts with sandy layer which becomes alternately saturated by sea water at high water tide and unsaturated at low water tide.
To secure the stability of steel pile structures, confirmation of corrosion rate of tie rod should be given. But, few corrosion survey of tie rod has been made because it is possible only when steel sheet pile structures are removed.
Therefore, corrosion survey of tie rod at Toyama Harbor and Shimokita Pier and a laboratory experiment on corrosion mechanism of tie rod were made, and the following results were obtained:
(1) Both tie rods, buried for 33 years at Toyama Harbor and for 40 years at Shimokita Pier, did almost not corrode.
(2) According to the laboratory experiment, it is assumed that steel sheet pile below residual water level acts as anode while tie rod as cathode, and at low water tide galvanic current of about 0.032 A/m², flows from anode to cathode while at high water tide current of about 0.023A/m² flows.
(3) If we expect (2), it is necessary that tie rod and steel sheet pile are in close contact.

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Resistance to initial atmospheric corrosion of commercially produced mild steel depends much on the property of oxide film which was formed on the surface when the steel was taken out of the annealing furnace.
It was found that the stability of oxide film could be determined by the time transition of the corrosion potential during immersion of a sample in a neutral solution. That is, when the sample was immersed in oxygen-free borate/HCl buffer solution of pH 7.65, both initial corrosion potential (E₀) and autoreduction time of oxide film (τ) could be adopted as the parameters for the stability of oxide film.
The shorter the time τ or the less noble the initial potential E₀ the greater the rate of rusting in humid air.
Moreover, an experimental relation 1/τ=7×10^-8 exp (-41.6E₀) was obtained between τ and E₀. If we assume that local cathodic reactions are identical for all the samples, the aboverelation could be derived from the theory of electrode reaction.

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