Abstract
The characteristics of electrolytic manganese (99.95%) as galvanic anode against mild steel sheets in river water (pH 6.6) and in artificial sea water were studied and the comparison was made with zinc anode (99.9964%). Corrosion rate of electrolytic Mn by simple immersion in river water was 1.39mdd. Anode potential of Mn in river water and in sea water was -1.2.- -0.75V and -1.3-1.1V (S. C. E.) respectively when anode current was held at 0.2-1mA/cm2 at room temperature, using carbon cathode. Mn anode could protect iron sheets about 30 times larger in area than the anode. Cathode (iron) potential became gradually less noble. Cathode potential and current after 600hrs. were -0.8V and 0.04mA/cm2 (river water) and -1.15V and 0.8mA/cm2 (sea water) when Mn was used as anode, while -0.76V and 0.01mA/cm2 (river water) and -1.10V and 0.06mA/cm2 (sea water) for zinc anode.
Mn galvanic anode showed in all cases a better protective action over mild steel sheets than zinc anode, especially in river water where perfect protection by zinc is difficult, but in sea water, Mn consumed rapidly in the amount of 3800-4500 mdd which was about 15 times larger than that in the case of zinc anode.
