Theory on the Square Wave Polarizations Under Controlled Current Conditions

Studies on Real Time Monitoring of Corrosion (Part 1)

Abstract

The potential change of corroding systems responding to the repetitive square wave current was deduced theoretically. The corroding systems were simulated by a linear circuit which was constructed with polarization resistance, solution resistance and capacitance due to electrical double layer. The potential change, where the response reached a steady state, was obtained as
δΔE_m=I₀[(R+R_s)M(t, 2p)-(2R(-1)ⁿexp{(n+1)p-t/CR})/(exp(p/CR)+1)]
where I₀ is the amplitude of applied square wave current, R_s, solution resistance, R polarization resistance, M unit square wave function, t time, p period of square wave, and n the maximum integer which does not exceed t/p. From this equation several ways of separating R, R_s, and C, from each other were proposed being based upon the following relations.
δΔE_m(t=np)=2I₀R_s, ΔE_p(p→∞)=ΔE_p(f→0)=2I₀(R+R_s)
ΔE_p(f→∞)=2R_s, {∂ΔE_p/∂(1/f)}_(1/f→0)=2I₀/C
where δΔE_m(t=np) is potential change at the instant of polarity change and ΔE_p is the peak-to-peak value of potential change. Finally, the feature of this method was discussed.