The corrosion behavior of mild steel was investigated in artificial sea water containing hydrogen sulfide, the concentration of which was controlled during an experimental period. The pH of this testing solution was controlled at 7.0. Instantaneous corrosion rate was measured by the linear polarization method. Relationship between the corrosion rate and the concentration of hydrogen sulfide was as follows. Before the surface of mild steel was not covered by sulfide film, the corrsoion rate was proportional to the concentration of hydrogen sulfide. But the corrosion rate in the higher concentration range showed larger dependance on the concentration than that in the lower or middle concentration range did. When a steady state was reached, the corrosion rate in the lower concentration range (<0.3μg-atom S/ml) was proportional to the concentration of hydrogen sulfide and no film formed. In the middle concentration range, (0.3-1.5μg-atom S/ml), the corrosion rate showed a constant small value because sulfide film covered the surface of the steel, and the corrosion rate did not change regardless of great increase or decrease in concentration. In the higher concentration range (>1.5μg-atom S/ml), the corrosion rate increased with a rise in concentration. The surface of the steel was also covered with sulfide film, but the corrosion resistance of this film was poor. After hydrogen sulfide was expelled from test solutions, these films decayed gradually with galvanic corrosion. These corrosion behaviors were almost the same as those observed in a culture of sulfate-reducing bacteria. That is, the corrosion of the steel seems to be caused by biogenetic hydrogen sulfide, not by the bacteria themselves.

抄録全体を表示

The mathematical calculation of the seawater resistance between rudder, propeller shaft and zinc anode of FRP Ship was performed with the interest to the corrosion protection of the boat. In the calculation, the rudder and the zinc anode, which were perpendicular each other, were converted into parallel plate condenser by the conformal transformation. The mathematical expression of the seawater resistance between the rudder and the zinc anode was obtained by the field mapping method, thus R₀=ρ⋅K₁′/K₁ for the zinc anode of infinite area and R=f₁⋅f₂⋅R₀ for that of finite area, where f₁ and f₂ indicate the seawater resistance coefficient on the X Z plane and XY plane respectively, ρ the resistivity of seawater, and K₁ and K₁′ indicate length and distance of electrode. A similar equations were also obtained for seawater resistance between the propeller shaft and the zinc anode. The results of the calculations were found to be in good agreement with the values measured on FRP Ship in real condition.

抄録全体を表示

A general review has been made of some of the major theories of stress corrosion cracking in aluminium alloys, mainly in Al-Zn-Mg alloys, with particular reference to the microstructural factors affecting an initiation and propagation of cracks along grain boundaries.
The roles of three main microstructural features, which have been claimed to have an important influence on the SCC behaviour; (1) the nature of the matrix precipitates, (2) the size and number of grain-boundary precipitates, (3) the width of the precipitate-free zone adjacent to the grain boundary were reviewed in detail. The importance of the size and distribution of the grain-boundary precipitates, which was closely dependent upon the structure of the grain boundary was emphasized in this alloy. Then some problems in development of alloys were also explained briefly, whereas the microstructural features have given a strong clue to explain the expected SCC behaviour, it must be also very important to study from an electrochemical stand point.

抄録全体を表示