Abstract
Relation between the corrosion rate and the shape of the potential response curve to an applied current step has been investigated for mild steel immersed in tap water as well as underground water. It was found that the potential response curve approached a straight line as the corrosion current density decreased, when the corrosion potential was more noble than -0.44V vs. SCE. In this case, it was also found that logarithm of the corrosion current density was proportionalto logarithm of ΔE4/ΔE10 in the corrosion current density range from 0.69μA/cm2 to 27.2μA/cm2, where ΔE4 and ΔE10 are overvoltage at 4 seconds and 10 seconds after application of current step. Corrosion current densities determined from ΔE4/ΔE10 values by the use of the regression equation agreed within 29% with those determined by the weight loss measurement. The surface state of the electrode was discussed and it was concluded that the electrode was in the active/passive transition region when the above dependence of ΔE4/ΔE10 values on the corrosion current densities existed.
