Method of evaluating the corrosion rates of metals

Details Method of evaluating the corrosion rates of metals Method of evaluating the corrosion rates of metals

1977-05-18

1978-12-19

Mack, John H.

Chemistry: electrical and wave energy

Processes and products

204195C, G01N 2746, G01N 2730

Patent

active

041304640

ABSTRACT:
A test piece of metal with a given area S is disposed with a reference electrode in test solution. The open circuit potential E.sub.cor, i.e. the corrosion potential, of the test piece is measured as the reference electrode potential. A given amount of charges q from a capacitor is instantaneously fed through the reference electrode to the electrical double layer of the test piece. When that a given amount of charge q is stored in the electrical double layer, the absolute value of polarization potential of the test piece sharply increases. Then, the absolute value of the polarization potential gradually decreases due to the corrosion reaction. The polarization potential variation is recorded referred to the reference electrode as a polarization potential (.eta..sub.t) - time (t) curve by a potential recorder with an extremely high input impedance. The measurement result of the polarization potential (.eta..sub.t) - time (t) curve may be theoretically expressed by the equation log .eta..sub.t = -t/(C.sub.D R.sub.p) + log .eta..sub.0. Therefore, the initial polarization potential .eta..sub.0 may be obtained by extrapolating the measurement result to the initial time t=0. The differential capacitance of the double layer C.sub.D can readily be calculated by the equation q/S = .DELTA.q = C.sub.D .eta..sub.0, and thus the polarization resistance R.sub.p is obtained from the measurement result. Since the polarization resistance R.sub.p is inversely proportional to the corrosion rate, the corrosion rate may be evaluated. The corrosion rate also is obtained from the polarization resistance R.sub.p by using a theoretical equation.

REFERENCES:
patent: 3616417 (1971-10-01), Wilson
M. Prazak, "The Polarization Resistance Method for Corrosion Testing", Werkstoffe und Korrosion, pp. 104-112 (1974).
"Techniques of Electrochemistry", vol. 1, Edited by E. Yeager et al., Wiley-Interscience, New York (1972), pp. 229-232.
I. Fried, "The Chemistry of Electrode Processes", Academic Press, New York (1973), pp. 151-152.
"Corrosion", vol. 2, Edited by L. L. Shreir, Newnes-Butterworths, London (1976), pp. 20-35 to 20-40.
P. J. Aragon et al., "Use of Charge Curve Analysis Technique for In-Vivo Determination of Corrosion Rates", Corrosion, vol. 30, pp. 432-436 (1974).

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