Kinetics of corrosion of passive metals. Part II: Failure of linear polarization technique

Abstract

To establish the degree of applicability of galvanostatic linear polarization technique to study the corrosion kinetics of passive metals, measurements were made with 6 typical passive metals which lead to the conclusion that no reliable or accurate data can be obtained in practice for such systems using the linear polarization technique. Shifts in the corrosion potential up to ±10 mV occur during polarization even when the quantity of electricity passed is negligibly small. The indeterminacy of corrosion potential arises from the absence of well-defined potential detg. reactions at the interface between a passive metal and solution. As a result, the exptl. values of polarization resistance may be highly misleading. Such a natural instability of corrosion potential on polarization tends to invalidate not only the linear polarization technique but also other small-signal perturbation technique and current or potential sweep techniques when applied to the detn. of the corrosion rate of passive metals