The Polarization Resistance Method for Corrosion Testing

Abstract

It is less than twenty years ago that potentiostatic measurements began t o be used t o a greater extent for following metal corrosion; this electrochemical method has then proven successful as a means for evaluating the corrosion properties of metals, especially those metals which are able to become passivated.Some time lateron, reports were published on another electrochemical method, involving measurements within the range of linear polarization of the electrode, i. e. the determination of the polarization resistance or polarization conductance of the corroding metal. From among the authors who have dealt with this method mention should be made of Stern and Geary ( 1 ) who summarized the theoretical basis of the method. The principle of the method, of course, is based on the classical work on the electrode potential theory by Wagner and T r a u d ; a number of authors then developed the method further (2-20).of the theoretical basis of the method itself, but rather a discussion of a number of problems in the field of electrochemistry and measuring techniques which are inseparably connected with the practical application of the method in laboratory o r industrial scale measurements. It seems that this method in particular tends t o expand from research laboratories towards a wider range of applications.calculating the corrosion current, i,,, from the slope of the polarization curve of the corroding metal at the zero net current point according to fig. 1. The aim of the present paper, however, is not an analysis Stern and Geary formulated the well-known relation forwhere A E = E -ECor has a sufficiently low value. may introduce errors into the calculations, which were dealt with b y P o u r b a i x (21) and Mansfeld and Oldham (17). In spite of that, however, it seems improbable that this simplification is the main source of errors in the application of the met hod. The simplification made b y Stern in deriving relation( 1) *) Plenary lecture at the 23rd Meeting of ISE, Stockholm 1972. + i $ 0 . . -i +E Fig. 1. Polarization curve in the vicinity of the corrosion potential. Some authors (8, 16, 22, 23) have used a modification of the Stern formula in which the term containing the slopes of the Tafel curves is replaced b y a single constant, B: B ico, = -RP (3) This additional simplification, of course, presumes that the constant B applies only t o a certain type of corrosion reaction determining the values of 0, and Pc, and that this is determined beforehand. This modification, in which the determination of the Tafel slopes is omitted, has a number of advantages, both from the point of view of simplification of the measuring technique, and from that of avoiding unwanted interference with the corrosion process. The measurenent of the Tafel curve and determination of the 0 values is often difficult. The theoretical linear log i vs E dependence is frequently disturbed by a number of factors among which transport processes are especially important. For example, in dilute and unbuffered solutions, the stationary catho...

Investigation of chloride‐induced pitting corrosion of steel in concrete with innovative methods

“…The anodic polarization resistance was calculated by using Ohm's law (Equation . The monitoring of corrosion development, measuring the polarization resistance, is used in several papers . Rp a 20 , anodic polarization resistance calculated by 20 s polarization time (Ωcm 2 ); Δ E , potential change (mV) (without the IR‐drop); i Rp current density (mAcm −2 ); I Rp , polarization current (mA); Area of pitting corrosion surface from CT data (cm 2 ).…”

Electrochemical Estimation of the Corrosion Rate of Magnesium/Aluminium Alloys

“…An alternative empiric estimation of B from the correlation between electrochemical and gravimetric measurements [27,28] is only appropriate if concurrent with the electrochemical corrosion there were no other corrosion processes of comparable rate, for example, metal disintegration. For instance, this estimation would not be possible in the case of commercially pure Mg due to the highly uneven corrosion attack suggesting undermining of metallic particles during the corrosion process (Figure 3).…”

Measurement of Electroless Plating Rate for Copper and Nickel Baths by Coulostatic Method

“…The other is a theoretical approach including direct measurement of Tafel slopes. The former method is widely used in electrochemical corrosion rate measurements (11) because the weight change is thought to be the most reliable measure for corrosion rate. The latter method seems to be ideal from a theoretical standpoint.…”