ASTM G106-89(2010)
(Practice)Standard Practice for Verification of Algorithm and Equipment for Electrochemical Impedance Measurements
Standard Practice for Verification of Algorithm and Equipment for Electrochemical Impedance Measurements
SIGNIFICANCE AND USE
The availability of a standard procedure, standard material, and standard plots should allow the investigator to check his laboratory technique. This practice should lead to electrochemical impedance curves in the literature which can be compared easily and with confidence.
Samples of a standard ferritic type 430 stainless steel (UNS 430000) used to obtain the reference plots are available for those who wish to check their equipment. Suitable resistors and capacitors can be obtained from electronics supply houses.
This test method may not be appropriate for electrochemical impedance measurements of all materials or in all environments.
SCOPE
1.1 This practice covers an experimental procedure which can be used to check one's instrumentation and technique for collecting and presenting electrochemical impedance data. If followed, this practice provides a standard material, electrolyte, and procedure for collecting electrochemical impedance data at the open circuit or corrosion potential that should reproduce data determined by others at different times and in different laboratories. This practice may not be appropriate for collecting impedance information for all materials or in all environments.
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.
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Standards Content (Sample)
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Designation:G106 −89(Reapproved 2010)
Standard Practice for
Verification of Algorithm and Equipment for Electrochemical
Impedance Measurements
This standard is issued under the fixed designation G106; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope G59TestMethodforConductingPotentiodynamicPolariza-
tion Resistance Measurements
1.1 This practice covers an experimental procedure which
can be used to check one’s instrumentation and technique for
3. Terminology
collecting and presenting electrochemical impedance data. If
followed, this practice provides a standard material,
3.1 Definitions—For definitions of corrosion related terms,
electrolyte, and procedure for collecting electrochemical im-
see Terminology G15.
pedance data at the open circuit or corrosion potential that
3.2 Symbols:
should reproduce data determined by others at different times
and in different laboratories. This practice may not be appro-
−2
priate for collecting impedance information for all materials or
C = capacitance (farad-cm )
in all environments.
Eʹ = real component of voltage (volts)
E" = imaginary component of voltage (volts)
1.2 The values stated in SI units are to be regarded as
E = complex voltage (volts)
standard. No other units of measurement are included in this
−1
f = frequency (s )
standard.
−2
Iʹ = real component of current (amp-cm )
−2
1.3 This standard does not purport to address all of the
I" = imaginary component of current (amp-cm )
−2
safety concerns, if any, associated with its use. It is the
I = complex current (amp-cm )
responsibility of the user of this standard to establish appro- j =
=21
priate safety and health practices and determine the applica-
L = inductance (henry−cm )
bility of regulatory limitations prior to use.
R = solution resistance (ohm-cm )
s
R = polarization resistance (ohm-cm )
p
2. Referenced Documents
R = charge transfer resistance (ohm-cm )
t
Zʹ = real component of impedance (ohm-cm )
2.1 ASTM Standards:
Z" = imaginary component of impedance (ohm-cm )
D1193Specification for Reagent Water
Z = complex impedance (ohm-cm )
G3Practice for Conventions Applicable to Electrochemical
α = phenomenological coefficients caused by depression
Measurements in Corrosion Testing
of the Nyquist plot below the real axis, α is the
G5Reference Test Method for Making Potentiodynamic
exponent and τ is the time constant(s).
Anodic Polarization Measurements
θ = phase angle (deg)
G15TerminologyRelatingtoCorrosionandCorrosionTest-
−1
ω = frequency (radians-s )
ing (Withdrawn 2010)
3.3 Subscripts:
This practice is under the jurisdiction ofASTM Committee G01 on Corrosion
ofMetalsandisthedirectresponsibilityofSubcommitteeG01.11onElectrochemi-
x = in-phase component
cal Measurements in Corrosion Testing.
y = out-of-phase component
Current edition approved May 1, 2010. Published May 2010. Originally
approved in 1989. Last previous edition approved in 2004 as G106–89(2004). DOI:
10.1520/G0106-89R10.
4. Summary of Practice
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
4.1 Reference impedance plots in both Nyquist and Bode
Standards volume information, refer to the standard’s Document Summary page on
formatareincluded.Thesereferenceplotsarederivedfromthe
the ASTM website.
3 results from nine different laboratories that used a standard
The last approved version of this historical standard is referenced on
www.astm.org. dummy cell and followed the standard procedure using a
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G106−89 (2010)
FIG. 1 Circuit Diagram for Dummy Cell Showing Positions for Hook-Up to Potentiostat
specific ferritic type alloy UNS-S43000 in 0.005 M H SO 6.2 Test Cell—The test cell should be constructed to allow
2 4
and 0.495 M Na SO . The plots for the reference material are the following items to be inserted into the solution chamber:
2 4
presentedasanenvelopethatsurroundsallofthedatawithand
the test electrode, two counter electrodes or a symmetrically
without inclusion of the uncompensated resistance. Plots for
arranged counter electrode around the working electrode, a
one data set from one laboratory are presented as well. Since
Luggin-Haber capillary with salt bridge connection to the
the results from the dummy cell are independent of laboratory,
reference electrode, an inlet and an outlet for an inert gas, and
only one set of results is presented.
a thermometer or thermocouple holder. The test cell must be
constructed of materials that will not corrode, deteriorate, or
4.2 A discussion of the electrochemical impedance
otherwise contaminate the solution.
technique, the physics that underlies it, and some methods of
interpretingthedataaregivenintheAppendixX1–Appendix 6.2.1 OnetypeofsuitablecellisdescribedinReferenceTest
X6. These sections are included to aid the individual in Method G5. Cells are not limited to that design. For example,
understanding the electrochemical impedance technique and a 1-L round-bottom flask can be modified for the addition of
some of its capabilities. The information is not intended to be
variousneckstopermittheintroductionofelectrodes,gasinlet
all inclusive. and outlet tubes, and the thermometer holder.ALuggin-Haber
capillaryprobecouldbeusedtoseparatethebulksolutionfrom
5. Significance and Use
the saturated calomel electrode. The capillary tip can be easily
adjusted to bring it into close proximity to the working
5.1 The availability of a standard procedure, standard
electrode. The minimum distance should be no less than two
material, and standard plots should allow the investigator to
capillary diameters from the working electrode.
check his laboratory technique. This practice should lead to
electrochemical impedance curves in the literature which can
6.3 Electrode Holder—The auxiliary and working elec-
be compared easily and with confidence.
trodes can be mounted in the manner shown in Reference Test
5.2 Samples of a standard ferritic type 430 stainless steel
Method G5. Precautions described in Reference Test Method
(UNS 430000) used to obtain the reference plots are available
G5 about assembly should be followed.
forthosewhowishtochecktheirequipment.Suitableresistors
6.4 Potentiostat—The potentiostat must be of the kind that
andcapacitorscanbeobtainedfromelectronicssupplyhouses.
allows for the application of a potential sweep as described in
5.3 This test method may not be appropriate for electro-
Reference Test Method G5 and Reference Practice G59. The
chemical impedance measurements of all materials or in all
potentiostat must have outputs in the form of voltage versus
environments.
ground for both potential and current. The potentiostat must
havesufficientbandwidthforminimalphaseshiftuptoatleast
6. Apparatus
1000Hzandpreferablyto10000Hz.Thepotentiostatmustbe
6.1 Dummy Cell—The dummy cell used to check the
capable of accepting an external excitation signal. Many
equipment and method for generating electrochemical imped-
commercial potentiostats meet the specification requirements
ance data is composed of a 10 Ω precision resistor placed in
for these types of measurements.
series with a circuit element composed of a 100 Ω precision
6.5 Collection and Analysis of Current-Voltage Response—
resistorinparallelwitha100µFcapacitor.Theresistorsshould
The potential and current measuring circuits must have the
have a stated precision of 60.1%. The capacitor can have a
characteristics described in Reference Test Method G5 along
precision of 620%. The cell can be constructed from readily
with sufficient band-width as described above. The impedance
available circuit elements by following the circuit diagram
can be calculated in several ways, for example, by means of a
shown in Fig. 1.
transferfunctionanalyzer,Lissajousfiguresonanoscilloscope,
ortransientanalysisofawhitenoiseinputusingaFastFourier
ThesestandardsamplesareavailablefromASTMHeadquarters.Generally,one Transform algorithm. Other methods of analysis exist.
sample can be repolished and reused for many runs. This procedure is suggested to
conserve the available material. 6.6 Electrodes:
G106−89 (2010)
FIG. 2 Nyquist Plot of Electrochemical Impedance Response for
FIG. 3 Bode Plot, Impedance Magnitude Versus Frequency, of
Dummy Cell
Electrochemical Impedance Response for Dummy Cell
6.6.1 Working electrode preparation should follow Refer-
ence Test Method G5, which involves drilling and tapping the
specimen and mounting it on the electrode holder.
6.6.2 Auxillary electrode preparation should follow Refer-
ence Test Method G5. The auxillary electrode arrangement
should be symmetrical around the working electrode.
6.6.3 Reference electrode type and usage should follow
Reference Test Method G5. The reference electrode is to be a
saturated calomel electrode.
7. Experimental Procedure
7.1 Test of Algorithm and Electronic Equipment (Dummy
Cell):
7.1.1 Measure the impedance of a dummy cell consisting of
a10 Ωresistorinserieswithaparallelcombinationofa100 Ω
resistor and a 100 µF capacitor. The circuit diagram is shown
in Fig. 1.
7.1.2 Typicalconnectionsfromthepotentiostatareshownin
Fig. 1. Connect the auxiliary electrode and reference electrode
leads to the series resistor side of the circuit. Connect the
FIG. 4 Bode Plot, Phase Angle Versus Frequency, of Electro-
working electrode lead to the opposite side of the circuit
chemical Impedance Response for Dummy Cell
beyond the resistor-capacitor parallel combination.
7.1.3 Set the potential at 0.0V. Collect the electrochemical
impedance data between 10 000 Hz (10 kHz) and 0.1 Hz (100
mHz) at 8 to 10 steps per frequency decade. The amplitude
7.2.1 Test specimens of the reference material should be
mustbethesameasthatusedtochecktheelectrochemicalcell,
prepared following the procedure described in Reference Test
10 mV. The resulting frequency response when plotted in
Method G5. This procedure involves polishing the specimen
Nyquist format (the negative of the imaginary impedance
with wet SiC paper with a final wet polish using 600 grit SiC
versustherealimpedance)mustagreewiththatshowninFigs.
paper prior to the experiment. There should be a maximum
2-4. Testing with the electrochemical cell should not be
delay of 1 h between final polishing and immersion in the test
attempteduntilthatagreementisestablished.Resultsusingthe
solution.
dummy circuit were found to be independent of laboratory.
7.2.2 Prepare a 0.495 M Na SO solution containing 0.005
2 4
7.2 Test of Electrochemical Cell: MH SO from reagent grade sulfuric acid and sodium sulfate
2 4
G106−89 (2010)
and Type IV reagent water described in Specification D1193.
The test is to be carried out at 30 6 1°C.
7.2.3 At least 1 h before specimen immersion, start purging
the solution with oxygen-free argon, hydrogen, or nitrogen gas
ataflowrateofabout100to150cm /min.Continuethepurge
throughout the test.
7.2.4 Transfer the specimen to the test cell. Adjust the
Luggin-Haber probe tip so that it is no less than two capillary
diameters from the sample. However, since this distance will
affect the uncompensated solution resistance, the greater the
distance, the larger the resistance. Therefore, close placement
is important.
7.2.5 Connect the potentiostat leads to the appropriate
electrodes, for example, working electrode lead to working
electrode, counter electrode lead to counter electrode, and
reference electrode lead to reference electrode. Hook-up in-
structions provided with the potentiostat must be followed.
7.2.6 Recordtheopencircuitpotential,thatis,thecorrosion
FIG. 5 Nyquist Plot of Typical Frequency Response for UNS-
potential,for1h.Thepotentialshouldbeabout−645 610mV
S43000 From One Laboratory
relative to the saturated calomel electrode. If the potential is
more positive than −600 mV (SCE) then the specimen may
have passivated. If so, remove the specimen and repolish with
600 grit wet silicon carbide paper. Then reimmerse the sample
and monitor the corrosion potential for 1 h. If the potential
again becomes more positive than −600 mV (SCE) check for
oxygen contamination of the solution.
7.2.7 Recordthefrequencyresponsebetween10000Hz(10
kHz)and0.1Hz(100mHz)atthecorrosionpotentialrecorded
after1hof exposure using 8 to 10 steps per frequency decade.
The amplitude must be the same as that used in 7.1.3,10mV.
7.2.8 Plot the frequency response in both Nyquist format
(real response versus the negative of the imaginary response)
and Bode format (impedance modulus and phase angle versus
frequency). Frequency can be reported in units of radians/
second or hertz (cycles/s).
7.2.9 Therewasnoattempttoestimatecircuitanaloguesfor
the electrochemical impedance curves since there is no univer-
sally recognized, standard method for making such estimates.
FIG. 6 Bode Plot, Impedance Magnitude Versus Frequency, for
8. Standard Reference Results and Plots
UNS-S43000 From One Laboratory
8.1 Dummy Cell:
8.1.1 The results from nine different laboratories were
8.2.2 The average solution resistance from the nine labora-
virtually identical and overlaid each other almost perfectly.
2 2
toriesin3.3 Ω-cm 61.8 Ω-cm (onestandarddeviation).The
TypicalplotsoftherawdataareshowninFigs.2-4.Noattempt
solution resistance of the user’s test cell as measured by the
has been made to estimate the variance and standard deviation
high frequency intercept on the Nyquist plot must lie in this
of the results from the nine laboratories. The measured values
range to use agreement with Figs. 8-10 for verification of the
of R,R , and the frequency at which the phase angle is a
s p
electrochemical test cell. If the uncompensated resistance lies
maximum must agree with these curves within the specifica-
outside of this range, it should be subtracted from the results
tions of the instrumentation, resistors, and capacitors before
(see 7.2.4).Then, results from the electrochemical test cell can
testing of the electrochemical cell commences. See 9.1.1.
be compared with the results in Figs. 11-13 to verify the test
8.2 Electrochemical Cell: cell. Figs. 11-13 envelop all of the results from the nine
laboratories with the uncompensated resistance subtracted out.
8.2.1 Standard electrochemical impedance plots in both
Nyquist format and Bode format are shown in Figs. 5-7.These
9. Precision and Bias
are actual results from one laboratory. F
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