The paper presents the results of comparative measurements of corrosion
rate by Coulometric Detection of Corrosion Products (CDCP method) and
voltammetry (VA). The corrosion kinetics was measured in the time interval where the
steady potential Est is established in the “carbon steel – 0.5 M NaCl solution” system as
an example. The results of measurements by both methods showed a considerable
difference in mass losses in the time interval of specimen surface activation. This fact
was explained taking the semiconducting nature of iron oxides into account. Thus, the
disagreement may originate from different conductance mechanisms of the metal and its oxides in a strong electric field.
The CDCP method was used to determine the conditions required for agreement of the results of potentiodynamic and
coulometric measurements. Application of the measuring capabilities of the CDCP method to determine the amount of
corrosion products allowed to:
1. record the kinetics in the microgram range, both during initial accumulation of corrosion products on the metal surface
before Est is reached and in the “protective effect” region of the oxide layers formed; 2. determine the conditions required
for agreement between the CDCP and VA methods: a balance should be established between the paces of accumulation of
the corrosion products formed on the specimen surface and accumulated in the liquid corrosive phase; 3. find out that if
polarization measurements are used, it is advisable to calibrate them by the CDCP method in order to take real mass losses
in the corrosion process into account.
Keywords: Corrosion kinetics, corrosion products, coulometry, measurement method.
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