チタンとステンレス鋼との電池作用腐食

抄録

The galvanic corrosion of commercially pure titanium coupled with 18-8 stainless steel was studied in various kinds of corrosive media. In reducing, acids, although the corrosion potential of titanium itself was in the active range and less noble than that of stainless steel, it was shifted into the passive range by coupling with stainless steel. Thus, titanium was anodically protected and its corrosion rate decreased remarkably, whereas the corrosion rate of stainless steel remained unchanged. For instance, titanium and stainless steel was perfectly resistant in 10% hydrochloric acid, 10% sulphuric acid and 10% oxalic acid solutions at room temperature, in which uncoupled titanium was corroded. This phenomenon of anodic protection was also observed in boiling 1% hydrochloric acid, 1% sulphuric acid and 0.5% oxalic acid solutions. In oxidizing acids, such as nitric acid, the galvanic corrosion was negligible, because the potentials of titanium and stainless steel were in their own passive ranges, and that of the couple was also in the passive range of both metals. In the case of boiling 99% acetic acid no galvanic corrosion was observed, either. In neutral chloride solutions, such as 3% sodium chloride solution, the potential of couple fluctuated and the direction of galvanic current changed irregularly because of the instability of protective film on stainless steel. However, the galvanic current was always less than 1 μA/cm², so that the galvanic corrosion was also negligible.