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ASTM G59-97(2014)
Standard Test Method for Conducting Potentiodynamic Polarization Resistance Measurements
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Разработчик:
Зарубежные/ASTM
ICS:
17.220.20 Measurement. Including measuring instruments, instrument transformers / Измерения электрических и магнитных величин. Включая измерительные приборы, измерительные трансформаторы
Сборник (ASTM):
03.02 Corrosion of Metals; Wear and Erosion / Коррозия металлов; Износ и разрушение (эрозия) металлов
Тематика:
Corrosion & Wear
Описание
Значение и использование

3.1 This test method can be utilized to verify the performance of polarization resistance measurement equipment including reference electrodes, electrochemical cells, potentiostats, scan generators, measuring and recording devices. The test method is also useful for training operators in sample preparation and experimental techniques for polarization resistance measurements.

3.2 Polarization resistance can be related to the rate of general corrosion for metals at or near their corrosion potential, Ecorr. Polarization resistance measurements are an accurate and rapid way to measure the general corrosion rate. Real time corrosion monitoring is a common application. The technique can also be used as a way to rank alloys, inhibitors, and so forth in order of resistance to general corrosion.

3.3 In this test method, a small potential scan, ΔE(t), defined with respect to the corrosion potential (ΔE = E – Ecorr), is applied to a metal sample. The resultant currents are recorded. The polarization resistance, RP, of a corroding electrode is defined from Eq 1 as the slope of a potential versus current density plot at i = 0 (1-4):3

Equation G0059-97R14_1

The current density is given by i. The corrosion current density, icorr, is related to the polarization resistance by the Stern-Geary coefficient, B. (3),

Equation G0059-97R14_2

The dimension of Rp is ohm-cm 2, icorr is muA/cm2, and B is in V. The Stern-Geary coefficient is related to the anodic, ba, and cathodic, bc, Tafel slopes as per Eq 3.

Equation G0059-97R14_3

The units of the Tafel slopes are V. The corrosion rate, CR, in mm per year can be determined from Eq 4 in which EW is the equivalent weight of the corroding species in grams and ρ is the density of the corroding material in g/cm 3.

Equation G0059-97R14_4

Refer to Practice G102 for derivations of the above equations and methods for estimating Tafel slopes.

3.4 The test method may not be appropriate to measure polarization resistance on all materials or in all environments. See 8.2 for a discussion of method biases arising from solution resistance and electrode capacitance.

Область применения

1.1 This test method covers an experimental procedure for polarization resistance measurements which can be used for the calibration of equipment and verification of experimental technique. The test method can provide reproducible corrosion potentials and potentiodynamic polarization resistance measurements.

1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

Ключевые слова:
anodic polarization; auxiliary electrode; cathodic polarization; corrosion; corrosion potential; corrosion rate; current density; electrochemical cell; electrochemical potential; Luggin probe; mixed potential; open-circuit potential; overvoltage; polarization resistance; potentiodynamic; reference electrode; solution resistance; Stern-Geary coefficient; Tafel slope; working electrode