抄録
Seven iron-silicon alloys having various silicon contents up to about 14% were polarized in 2 N H2SO4. The relationship between silicon contents in the alloys and various properties such as the maximum or the limitting current density and the passive potential and the passive current density were investigated. 14% silicon alloy is much easier to passivate than iron, because the maxmum current density of the 14% alloy is equivalent to one-hundredth as large as that of iron and the passivation potential of the 14% alloy is close to its corrosion potential. An unusual variation in the passive current density with silicon content was observed; the passive current density increased with increasing Si content up to 6%, but decreased with increasing Si content above 6%.
The anodic polarization measurements were also carried out in 1 and 0.5 N H2SO4 with three iron specimens, 6 and 14% Si. The polarization behavior of the 6% alloy was only affeted by the sulphuric acid concentration. In 1 and 0.5 N H2SO4, the transition region from the active to passive state of the 6% alloy extended to the noble potential side accompanying a violent current oscillation. Such passivation phenomena can be explained to some extent on the basis of the silica formation on the anode surface.
