ASTM G3-89(2004)
(Practice)Standard Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing
Standard Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing
SIGNIFICANCE AND USE
This practice provides guidance for reporting, displaying, and plotting electrochemical corrosion data and includes recommendations on signs and conventions. Use of this practice will result in the reporting of electrochemical corrosion data in a standard format, facilitating comparison between data developed at different laboratories or at different times. The recommendations outlined in this standard may be utilized when recording and reporting corrosion data obtained from electrochemical tests such as potentiostatic and potentiodynamic polarization, polarization resistance, electrochemical impedance and admittance measurements, galvanic corrosion, and open circuit potential measurements.
SCOPE
1.1 This practice covers conventions for reporting and displaying electrochemical corrosion data. Conventions for potential, current density, electrochemical impedance and admittance, as well as conventions for graphical presentation of such data are included.
1.2 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.
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Designation:G3–89(Reapproved 2004)
Standard Practice for
Conventions Applicable to Electrochemical Measurements
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in Corrosion Testing
This standard is issued under the fixed designation G3; the number immediately following the designation indicates the year of original
adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 4. Sign Convention for Electrode Potential
1.1 This practice covers conventions for reporting and 4.1 The Stockholm sign invariant convention is recom-
displaying electrochemical corrosion data. Conventions for mended for use in reporting the results of specimen potential
potential, current density, electrochemical impedance and ad- measurements in corrosion testing. In this convention, the
mittance, as well as conventions for graphical presentation of positivedirectionofelectrodepotentialimpliesanincreasingly
such data are included. oxidizing condition at the electrode in question. The positive
1.2 This standard does not purport to address all of the direction has also been denoted as the noble direction because
safety concerns, if any, associated with its use. It is the thecorrosionpotentialsofmostnoblemetals,suchasgold,are
responsibility of the user of this standard to establish appro- more positive than the nonpassive base metals. On the other
priate safety and health practices and determine the applica- hand,thenegativedirection,oftencalledtheactivedirection,is
bility of regulatory limitations prior to use. associated with reduction and consequently the corrosion
potentials of active metals, such as magnesium. This conven-
2. Referenced Documents
tionwasadoptedunanimouslybythe1953InternationalUnion
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2.1 ASTM Standards: of Pure and Applied Chemistry as the standard for electrode
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IEEE/ASTM SI 10 Standard for Use of the International
potential (1).
System of Units (SI) (the Modern Metric System) 4.2 In the context of a specimen electrode of unknown
potential in an aqueous electrolyte, consider the circuit shown
3. Significance and Use
in Fig. 1 with a reference electrode connected to the ground
3.1 This practice provides guidance for reporting, display-
terminal of an electrometer. If the electrometer reads on scale
ing, and plotting electrochemical corrosion data and includes
when the polarity switch is negative, the specimen electrode
recommendations on signs and conventions. Use of this prac-
potential is negative (relative to the reference electrode).
tice will result in the reporting of electrochemical corrosion
Conversely, if the electrometer reads on scale when polarity is
datainastandardformat,facilitatingcomparisonbetweendata
positive, the specimen potential is positive. On the other hand,
developed at different laboratories or at different times. The
if the specimen electrode is connected to the ground terminal,
recommendations outlined in this standard may be utilized
the potential will be positive if the meter is on scale when the
when recording and reporting corrosion data obtained from
polarity switch is negative, and vice versa.
electrochemical tests such as potentiostatic and potentiody-
NOTE 1—In cases where the polarity of a measuring instrument is in
namic polarization, polarization resistance, electrochemical
doubt, a simple verification test can be performed as follows: connect the
impedance and admittance measurements, galvanic corrosion,
measuring instrument to a dry cell with the lead previously on the
and open circuit potential measurements.
referenceelectrodetothenegativebatteryterminalandtheleadpreviously
on the specimen electrode to the positive battery terminal. Set the range
switchtoaccommodatethedrycellvoltage.Themeterdeflectionwillnow
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This practice is under the jurisdiction ofASTM Committee G01 on Corrosion
show the direction of positive potential.
ofMetalsandisthedirectresponsibilityofSubcommitteeG01.11onElectrochemi-
Also, the corrosion potential of magnesium or zinc should be negative
cal Measurements in Corrosion Testing.
ina1 N NaCl solution if measured against a saturated standard calomel
Current edition approved Nov 1, 2004. Published November 2004. Originally
electrode (SCE).
approved in 1968. Last previous edition approved in 1999 as G3–89 (1999). DOI:
10.1520/G0003-89R04.
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For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
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Standards volume information, refer to the standard’s Document Summary page on Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
the ASTM website. this practice.
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