ASTM G59-97(2009)

Standard Test Method for Conducting Potentiodynamic Polarization Resistance Measurements

SIGNIFICANCE AND USE
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.
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.
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):
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),
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.
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/cm3.
Refer to Practice G 102 for derivations of the above equations and methods for estimating Tafel slopes.
The test method may not be appropriate to measure polarization resistance on all materials or in all environments. See 9.2 for a discussion of method biases arising from solu...
SCOPE
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.

General Information

• Status: Historical
• Publication Date: 30-Apr-2009
• ICS: 17.220.20 - Measurement of electrical and magnetic quantities
• Technical Committee: G01 - Corrosion of Metals
• Drafting Committee: G01.11 - Electrochemical Measurements in Corrosion Testing

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: G59 − 97(Reapproved 2009)
Standard Test Method for
Conducting Potentiodynamic Polarization Resistance
Measurements
ThisstandardisissuedunderthefixeddesignationG59;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope sample preparation and experimental techniques for polariza-
tion resistance measurements.
1.1 This test method covers an experimental procedure for
polarizationresistancemeasurementswhichcanbeusedforthe 3.2 Polarization resistance can be related to the rate of
calibration of equipment and verification of experimental generalcorrosionformetalsatorneartheircorrosionpotential,
technique. The test method can provide reproducible corrosion E .Polarizationresistancemeasurementsareanaccurateand
corr
potentials and potentiodynamic polarization resistance mea- rapid way to measure the general corrosion rate. Real time
surements. corrosion monitoring is a common application. The technique
canalsobeusedasawaytorankalloys,inhibitors,andsoforth
1.2 The values stated in SI units are to be regarded as
in order of resistance to general corrosion.
standard. No other units of measurement are included in this
standard. 3.3 Inthistestmethod,asmallpotentialscan,∆E(t),defined
with respect to the corrosion potential (∆E=E–E ), is
corr
1.3 This standard does not purport to address all of the
applied to a metal sample. The resultant currents are recorded.
safety concerns, if any, associated with its use. It is the
The polarization resistance, R , of a corroding electrode is
P
responsibility of the user of this standard to establish appro-
defined from Eq 1 as the slope of a potential versus current
priate safety and health practices and determine the applica-
density plot at i=0 (1-4):
bility of regulatory limitations prior to use.
] ∆E
R 5 (1)
S D
p
2. Referenced Documents
] i
i50, dE/dt→0
2.1 ASTM Standards:
The current density is given by i. The corrosion current
G3 Practice for Conventions Applicable to Electrochemical
density, i , is related to the polarization resistance by the
corr
Measurements in Corrosion Testing
Stern-Geary coefficient, B. (3),
G5 Reference Test Method for Making Potentiostatic and
B
Potentiodynamic Anodic Polarization Measurements 6
i 5 10 (2)
corr
R
p
G102 Practice for Calculation of Corrosion Rates and Re-
2 2
lated Information from Electrochemical Measurements
The dimension of R is ohm-cm , i is muA/cm , and B is
p corr
in V. The Stern-Geary coefficient is related to the anodic, b ,
a
3. Significance and Use
and cathodic, b , Tafel slopes as per Eq 3.
c
3.1 This test method can be utilized to verify the perfor-
b b
a c
B 5 (3)
mance of polarization resistance measurement equipment in-
2.303~b 1b !
a c
cluding reference electrodes, electrochemical cells,
The units of the Tafel slopes are V. The corrosion rate, CR,
potentiostats, scan generators, measuring and recording de-
in mm per year can be determined from Eq 4 in which EW is
vices. The test method is also useful for training operators in
the equivalent weight of the corroding species in grams andρ
is the density of the corroding material in g/cm .
i EW
corr
This test method is under the jurisdiction of ASTM Committee G01 on
CR 5 3.27 310 (4)
Corrosion of Metals and is the direct responsibility of Subcommittee G01.11 on ρ
Electrochemical Measurements in Corrosion Testing.
Refer to Practice G102 for derivations of the above equa-
Current edition approved May 1, 2009. Published May 2009. Originally
approved in 1978. Last previous edition approved in 2003 as G59–97(2003). DOI:
tions and methods for estimating Tafel slopes.
10.1520/G0059-97R09.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The boldface numbers in parentheses refer to the list of references at the end of
the ASTM website. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G59 − 97(Reapproved 2009)
3.4 The test method may not be appropriate to measure
polarization resistance on all materials or in all environments.
G59 − 97 (2009)
See 8.2 for a discussion of method biases arising from solution 6.2 The test cell is purged at 150 cm /min with an oxygen-
resistance and electrode capacitance. free gas such as hydrogen, nitrogen, or argon. The purge is
started at least 30 min before specimen immersion. The purge
4. Apparatus
continues throughout the test.
4.1 The apparatus is described in Test Method G5.It
6.3 The working electrode should be prepared as detailed in
includesa1L round bottom flask modified to permit the
TestMethodG5.Theexperimentmustcommencewithin1hof
addition of inert gas, thermometer, and electrodes. This stan-
preparing the electrode. Preparation includes sequential wet
dard cell or an equivalent cell can be used. An equivalent cell
polishing with 240 grit and 600 grit SiC paper. Determine the
must be constructed of inert materials and be able to reproduce
surface area of the specimen to the nearest 0.01 cm and
the standard curve in Test Method G5.
subtract for the area under the gasket (typically 0.20 to 0.25
cm ).
4.2 Apotentiostat capable of varying potential at a constant
scan rate and measuring the current is needed.
6.4 Immediately prior to immersion the specimen is
4.3 A method of recording the varying potential and result- degreased with a solvent such as acetone and rinsed with
ing current is needed. distilled water. The time delay between rinsing and immersion
should be minimal.
5. Test of Electrical Equipment
NOTE 2—Samples of the standard AISI Type 430 stainless steel (UNS
5.1 Beforethepolarizationresistancemeasurementismade,
S45000)usedinthistestmethodareavailabletothosewishingtoevaluate
the instrument system (potentiostat, X-Y recorder or data their equipment and test procedure from Metal Samples, P.O. Box 8,
Mumford, AL 36268.
acquisition system) must be tested to ensure proper function-
ing. For this purpose, connect the potentiostat to a test
6.5 Transfer the test specimen to the test cell and position
electrical circuit (5). While more complex dummy cells are
the Luggin probe tip 2 to 3 mm from the test electrode surface.
sometimes needed in electrochemical studies, the simple resis-
The tip diameter must be no greater than 1 mm.
tor shown in Fig. 1 is adequate for the present application.
6.6 Record the corrosion potential E after 5 and 55-min
corr
5.2 Use R = 10.0 Ω. Set the applied potential on the
immersion.
potentiostat to E =– 30.0 mV and apply the potential. The
6.7 Apply a potential 30 mV more negative that the re-
current should be 3.0 mA by Ohm’s Law, I = E/R.
corded 55 min corrosion potential (See Note 3).
NOTE 1—When polarization resistance values are measured for systems
NOTE 3—Practice G3 provides a definition of sign convention for
with different corrosion currents, the value of R should be chosen to cover
potential and current.
the current range of the actual polarization resistance measurement.
Expected corrosion cu
...