ASTM G5-94(2011)e1
(Test Method)Standard Reference Test Method for Making Potentiostatic and Potentiodynamic Anodic Polarization Measurements
Standard Reference Test Method for Making Potentiostatic and Potentiodynamic Anodic Polarization Measurements
SIGNIFICANCE AND USE
The availability of a standard procedure, standard material, and a standard plot should make it easy for an investigator to check his techniques. This should lead to polarization curves in the literature which can be compared with confidence.
Samples of a standard ferritic Type 430 stainless steel (UNS S43000) used in obtaining standard reference plot are available for those who wish to check their own test procedure and equipment.
Standard potentiostatic and potentiodynamic polarization plots are supplied with the purchase of the reference material. These reference data are based on the results from different laboratories that followed the standard procedure, using that material in 1.0 N H2SO4. Maximum and minimum current values are shown at each potential to indicate the acceptable range of values.
This test method may not be appropriate for polarization testing of all materials or in all environments.
This test method is intended for use in evaluating the accuracy of a given electrochemical test apparatus, not for use in evaluating materials performance. Therefore, the use of the plots in Figs. 1 and 2 or Appendix X2 is not recommended to evaluate alloys other than Type 430, or lots of Type 430 other than those available through ASTM. The use of the data in this test method in this manner is beyond the scope and intended use of this test method. Users of this test method are advised to evaluate test results relative to the scatter bands corresponding to the particular lot of Type 430 stainless steel that was tested.
CURRENT DENSITY (μA/cm2)
FIG. 1 Typical Standard Potentiostatic Anodic Polarization Plot
CURRENT DENSITY (μA/cm2)
FIG. 2 Typical Standard Potentiodynamic Anodic Polarization Plot
SCOPE
1.1 This test method covers an experimental procedure for checking experimental technique and instrumentation. If followed, this test method will provide repeatable potentiostatic and potentiodynamic anodic polarization measurements that will reproduce data determined by others at other times and in other laboratories provided all laboratories are testing reference samples from the same lot of Type 430 stainless steel.
1.2 Units—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
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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
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Designation: G5 − 94(Reapproved 2011)
Standard Reference Test Method for
Making Potentiostatic and Potentiodynamic Anodic
Polarization Measurements
This standard is issued under the fixed designation G5; 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.
´ NOTE—Updated units statement and text editorially in November 2011.
1. Scope investigator to check his techniques. This should lead to
polarization curves in the literature which can be compared
1.1 This test method covers an experimental procedure for
with confidence.
checking experimental technique and instrumentation. If
followed, this test method will provide repeatable potentio- 3.2 Samples of a standard ferritic Type 430 stainless steel
static and potentiodynamic anodic polarization measurements (UNS S43000) used in obtaining standard reference plot are
that will reproduce data determined by others at other times available for those who wish to check their own test procedure
and in other laboratories provided all laboratories are testing and equipment.
referencesamplesfromthesamelotofType430stainlesssteel.
3.3 Standard potentiostatic and potentiodynamic polariza-
1.2 Units—The values stated in SI units are to be regarded tion plots are supplied with the purchase of the reference
asstandard.Nootherunitsofmeasurementareincludedinthis material. These reference data are based on the results from
standard. different laboratories that followed the standard procedure,
using that material in 1.0 N H SO . Maximum and minimum
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1.3 This standard does not purport to address all of the
current values are shown at each potential to indicate the
safety concerns, if any, associated with its use. It is the
acceptable range of values.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
3.4 Thistestmethodmaynotbeappropriateforpolarization
bility of regulatory limitations prior to use.
testing of all materials or in all environments.
3.5 This test method is intended for use in evaluating the
2. Referenced Documents
accuracy of a given electrochemical test apparatus, not for use
2.1 ASTM Standards:
in evaluating materials performance. Therefore, the use of the
E1338Guide for Identification of Metals and Alloys in
plots in Figs. 1 and 2 or Appendix X2 is not recommended to
Computerized Material Property Databases
evaluate alloys other than Type 430, or lots of Type 430 other
G3Practice for Conventions Applicable to Electrochemical
than those available throughASTM.The use of the data in this
Measurements in Corrosion Testing
test method in this manner is beyond the scope and intended
G107Guide for Formats for Collection and Compilation of
useofthistestmethod.Usersofthistestmethodareadvisedto
Corrosion Data for Metals for Computerized Database
evaluate test results relative to the scatter bands corresponding
Input
to the particular lot of Type 430 stainless steel that was tested.
3. Significance and Use
4. Apparatus
3.1 The availability of a standard procedure, standard
4.1 The test cell should be constructed to allow the follow-
material, and a standard plot should make it easy for an
ing items to be inserted into the solution chamber: the test
electrode, two auxiliary electrodes, a Luggin capillary with
salt-bridge connection to the reference electrode, inlet and
This test method is under the jurisdiction of ASTM Committee G01 on
outletforaninertgas,andathermometer.Thetestcellshallbe
Corrosion of Metals and is the direct responsibility of G01.11 on Electrochemical
constructed of materials that will not corrode, deteriorate, or
Measurements in Corrosion Testing.
Current edition approved Nov. 15, 2011. Published May 2012. Originally
otherwise contaminate the test solution.
approved in 1969. Last previous edition approved in 2004 as G5–94(2004). DOI:
10.1520/G0005-94R11E01.
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 These standard samples are available from Metal Samples, P.O. Box 8,
Standards volume information, refer to the standard’s Document Summary page on Mumford,AL36268. Generally, one sample can be repolished and reused for many
the ASTM website. runs. This procedure is suggested to conserve the available material.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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G5 − 94 (2011)
CURRENT DENSITY (µA/cm )
FIG. 1 Typical Standard Potentiostatic Anodic Polarization Plot
CURRENT DENSITY (µA/cm )
FIG. 2 Typical Standard Potentiodynamic Anodic Polarization Plot
NOTE 1—Borosilicate glass and TFE-fluorocarbon have been found
separates the bulk solution from the saturated calomel refer-
suitable.
enceelectrode,andtheprobetipcanbeeasilyadjustedtobring
4.1.1 A suitable cell is shown in Fig. 3 (1). A 1-L,
it in close proximity with the working electrode.
roundbottomflaskhasbeenmodifiedbytheadditionofvarious
4.2 Potentiostat (Note 2):
necks to permit the introduction of electrodes, gas inlet and
4.2.1 Apotentiostatthatwillmaintainanelectrodepotential
outlet tubes, and a thermometer. The Luggin probe-salt bridge
within 1 mV of a preset value over a wide range of applied
currents should be used. For the type and size of standard
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this test method.
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G5 − 94 (2011)
FIG. 3 Schematic Diagram of Polarization Cell (1)
FIG. 4 Schematic Potentiostatic Anodic Polarization
specimen supplied, the potentiostat should have a potential Wiring Diagram (2)
range from−0.6 to 1.6 V and an anodic current output range
from 1.0 to 10 µA.
4.3 Potential-Measuring Instruments (Note 2):
4.3.1 The potential-measuring circuit should have a high
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input impedance on the order of 10 to 10 Ω to minimize
current drawn from the system during measurements. Such
circuits are provided with most potentiostats. Instruments
should have sufficient sensitivity and accuracy to detect a
change of 1.0 mVover a potential range between−0.6 and 1.6
V.
4.4 Current-Measuring Instruments (Note 2):
4.4.1 An instrument that is capable of measuring a current
accurately to within 1% of the absolute value over a current
range between 1.0 and 10 µA for a Type 430 stainless steel
(UNS S43000) specimen with a surface area of approximately
5cm .
4.5 Anodic Polarization Circuit:
4.5.1 A schematic potentiostatic anodic polarization wiring
diagram (2) is illustrated in Fig. 4.
4.5.2 A scanning potentiostat is used for potentiodynamic
measurements.Forsuchmeasurementsthepotentiostatshallbe
capableofautomaticallyvaryingthepotentialataconstantrate
between two preset potentials. A record of the potential and
current is plotted continuously using such instruments as an
X-Y recorder and a logarithmic converter incorporated into the
FIG. 5 Specimen Mounted on Electrode Holder
circuit shown in Fig. 4. Some potentiostats have an output of
the logarithm of the current as a voltage, which allows direct
plotting of the potential log current curve using an X-Y
age of the glass holder, and too little pressure may cause
recorder.
leakage and subsequently crevice corrosion which may affect
the test results.)
NOTE 2—The instrumental requirements are based upon values typical
of the instruments in 15 laboratories.
4.7 Electrodes:
4.6 Electrode Holder (1):
4.7.1 Working Electrode, prepared from a 12.7-mm length
4.6.1 The auxiliary and working electrodes are mounted in
of 9.5-mm diameter rod stock. Each electrode is drilled,
the type of holder shown in Fig. 5.Alonger holder is required
tapped, and mounted in the manner discussed in 4.6.1.
for the working electrode than for the auxiliary electrode. A
NOTE 3—If specimen forms are used other than those called for by this
leak-proof assembly is obtained by the proper compression fit
test method, for example, flat sheet specimen, care should be taken since
between the electrode and a TFE-fluorocarbon gasket. (Too
itwasshownthatcrevicesmaybeintroducedwhichcanleadtoerroneous
much pressure may cause shielding of the electrode or break- results (see Fig. X1.1).
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G5 − 94 (2011)
stopcock can be used in the salt bridge to eliminate siphoning, or a
4.7.1.1 The standard AISI Type 430 stainless steel (UNS
semi-permeable membrane or porous plug tip may be used on the salt
S43000) should be used if one wishes to reproduce a standard
bridge.
reference plot. This material is prepared from a single heat of
5.3 Bring the temperature of the solution to 30 6 1°C by
metal that is mill-annealed for ⁄2 h at 815°C and air cooled.
immersing the test cell in a controlled-temperature water bath
The chemical composition of the standard stainless steel is
or by other convenient means.
supplied with the purchase of reference material.
4.7.2 Auxiliary Electrodes:
5.4 Reduce oxygen levels in solution prior to immersion of
4.7.2.1 Twoplatinumauxiliaryelectrodesarepreparedfrom the test specimen. This may be accomplished by bubbling an
oxygen-free gas such as hydrogen, argon, or nitrogen at a rate
high-purity rod stock. Each electrode is drilled, tapped, and
mounted with a TFE-fluorocarbon gasket in the same manner of 150 cm /min for a minimum of ⁄2 h.
as the working electrode. A large platinum sheet sealed into a
5.5 Prepare the working electrode surface within1hofthe
glass holder is also acceptable.
experiment.Wetgrindwith240-gritSiCpaper,wetpolishwith
4.7.2.2 A platinized surface may be utilized because of the
600-gritSiCpaperuntilpreviouscoarsescratchesareremoved,
increased surface area. This may be accomplished by cleaning
rinse, and dry. (Drilled and tapped specimens can be threaded
the surface in hot aqua regia (3 parts concentrated HCl and 1
onto an electrode holder rod and secured in a lathe or electric
part concentrated HNO ), washing, and then drying. Both
drill for this operation.)
electrodes are platinized by immersing them in a solution of
5.6 Determinethesurfaceareabymeasuringalldimensions
3%platinicchlorideand0.02%leadacetateandelectrolyzing
to the nearest 0.01 mm, subtracting the area under the gasket
at a current density of 40 to 50 mA/cm for4or5min (1, 3).
(usually 0.20 to 0.25 cm ).
The polarity is reversed every minute. Occluded chloride is
5.7 Mount the specimen on the electrode holder as de-
removed by electrolyzing in a dilute (10%) sulfuric acid
scribedin4.6.1.Tightentheassemblybyholdingtheupperend
solution for several minutes with a reversal in polarity every
of the mounting rod in a vise or clamp while tightening the
minute.Electrodesarerinsedthoroughlyandstoredindistilled
mounting nut until the gasket is properly compressed.
water until ready for use. Since certain ions can poison these
electrodes, periodic checks of platinized platinum potentials
5.8 Degrease the specimen just prior to immersion and then
against a known reference electrode should be made.
rinse in distilled water.
4.7.2.3 Alternatively, graphite auxiliary electrodes can be
5.9 Transfer the specimen to the test cell and adjust the
used, but material retained by the graphite may contaminate
salt-bridge probe tip so it is about 2 mm or 2 times the tip
subsequentexperiments.Thiscontaminationcanbeminimized
diameter, whichever is larger from the specimen electrode.
by using high-density graphite or avoided by routinely replac-
5.10 Record the open-circuit specimen potential, that is, the
ing the graphite electrode.
corrosion potential, after 55 min immersion. If platinum
4.7.3 Reference Electrode (4):
counter electrodes and hydrogen gas are used, record the
4.7.3.1 Asaturated calomel electrode with a controlled rate
platinum potential 50 min after immersion of the specimen.
of leakage (about 3 µL/h) is recommended. This type of
electrode is durable, reliable, and commercially available. 5.11 Potential Scan:
Precautions shall be taken to ensure that it is maintained in the
5.11.1 Start the potential scan or step 1 h after specimen
propercondition.Thepotentialofthecalomelelectrodeshould immersion, beginning at the corrosion potential (E ) for
corr
be checked at periodic intervals to ensure the accuracy of the
potentiodynamic measurements and the nearest 50-mV incre-
electrode. For other alloy-electrolyte combinations a different ment above E for the potentiostatic measurements. Proceed
corr
reference electrode may be preferred in order to avoid con-
through+1.60 V versus saturated calomel electrode (SCE)
tamination of the reference electrode or the electrolyte. (active to noble).
5.11.2 In the potentiostatic method, use a potentiostatic
4.7.3.2 Alternatively, a saturated calomel electrode utilizing
potential step rate of 50 mVevery 5 min, recording the current
a semi-permeable membrane or porous plug tip may be used.
These may require special care. at the end of each 5-min period at potential. These steps are
repeated until a potential of+1.6 V SCE is reached.
5.11.3 In the potentiodynamic method, use a potentiody-
5. Experimental Procedure
namic potential sweep rate of 0.6 V/h (65%) recording the
5.1 Prepare 1 L of 1.0 N H SO fromA.C.S. reagent grade
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current continuously with change in potential from the corro-
acidanddistilledwater,forexample,byusing27.8mLof98%
sion potential to+1.6 V SCE.
H SO /Lof solution.Transfer 900 mLof solution to the clean
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5.12 Plot anodic polarization data on semilogarithmic paper
polarization cell.
in accordance with Practice G3, (potential-ordinate, current
5.2 Place the platinized auxiliary electrodes, salt-bridge
density-abscissa).Ifapotentiostatwithalogarithmicconverter
probe, and other components in the test cell and temporarily
is used, this plot can be produced directly during the measure-
close the center opening with a glass stopper. Fill the salt
ment.
bridge with test solution.
6. Standard Reference Plots
NOTE 4—When using a controlled leakage salt bridge, the levels of the
6.1 Standard polarization plots prepared from data obtained
solutioninthereferenceandpolarizationcellsshouldbethesametoavoid
siphoning. If this is impossible, a closed solution-wet (not greased) by following the standard procedure discussed in this test
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G5 − 94 (2011)
method are supplied with the purchase of reference material. areattributedtominordifferencesinthetwoheatsofType430
TypicaldataareshowninFig.1andFig.2 (5).Theplotsshow stainless steel that were evaluated in separa
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