ASTM G106-89(2015)

Standard Practice for Verification of Algorithm and Equipment for Electrochemical Impedance Measurements

SIGNIFICANCE AND USE
5.1 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.  
5.2 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.  
5.3 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.

General Information

• Status: Historical
• Publication Date: 31-Oct-2015
• ICS: 71.040.40 - Chemical analysis
• 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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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: G106 − 89 (Reapproved 2015)
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. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope G59 Test Method for Conducting Potentiodynamic Polariza-
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 =
=
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 )
D1193 Specification for Reagent Water
Z = complex impedance (ohm-cm )
G3 Practice 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
G5 Reference Test Method for Making Potentiodynamic
exponent and τ is the time constant(s).
Anodic Polarization Measurements
θ = phase angle (deg)
G15 Terminology Relating to Corrosion and Corrosion Test-
−1
ω = frequency (radians-s )
ing (Withdrawn 2010)
3.3 Subscripts:
This practice is under the jurisdiction of ASTM Committee G01 on Corrosion
of Metals and is the direct responsibility of Subcommittee G01.11 on Electrochemi-
x = in-phase component
cal Measurements in Corrosion Testing.
y = out-of-phase component
Current edition approved Nov. 1, 2015. Published December 2015. Originally
approved in 1989. Last previous edition approved in 2010 as G106–89(2010). DOI:
10.1520/G0106-89R15.
4. Summary of Practice
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. 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
format are included. These reference plots are derived from the
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 (2015)
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
presented as an envelope that surrounds all of the data with and 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
interpreting the data are given in the Appendix X1 – Appendix 6.2.1 One type of suitable cell is described in Reference Test
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 various necks to permit the introduction of electrodes, gas inlet
all inclusive.
and outlet tubes, and the thermometer holder. A Luggin-Haber
capillary probe could be used to separate the bulk solution from
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.
for those who wish to check their equipment. Suitable resistors
6.4 Potentiostat—The potentiostat must be of the kind that
and capacitors can be obtained from electronics supply houses.
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
have sufficient bandwidth for minimal phase shift up to at least
6. Apparatus
1000 Hz and preferably to 10 000 Hz. The potentiostat must be
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—
resistor in parallel with a 100 µF capacitor. The resistors should
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.
transfer function analyzer, Lissajous figures on an oscilloscope,
or transient analysis of a white noise input using a Fast Fourier
These standard samples are available from ASTM Headquarters. 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 (2015)
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
a 10 Ω resistor in series with a parallel combination of a 100 Ω
resistor and a 100 µF capacitor. The circuit diagram is shown
in Fig. 1.
7.1.2 Typical connections from the potentiostat are shown in
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 0.0 V. 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 ampli-
7.2.1 Test specimens of the reference material should be
tude must be the same as that used to check the electrochemical
prepared following the procedure described in Reference Test
cell, 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
versus the real impedance) must agree with that shown in Figs.
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
attempted until that agreement is established. Results using the
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: M H SO from reagent grade sulfuric acid and sodium sulfate
2 4
G106 − 89 (2015)
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
at a flow rate of about 100 to 150 cm /min. Continue the purge
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 Record the open circuit potential, that is, the corrosion
FIG. 5 Nyquist Plot of Typical Frequency Response for UNS-
potential, for 1 h. The potential should be about −645 6 10 mV
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 Record the frequency response between 10 000 Hz
(10 kHz) and 0.1 Hz (100 mHz) at the corrosion potential
recorded after 1 h of exposure using 8 to 10 steps per frequency
decade. The amplitude must be the same as that used in 7.1.3,
10 mV.
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 There was no attempt to estimate circuit analogues for
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-
2 2
virtually identical and overlaid each other almost perfectly.
tories in 3.3 Ω-cm 6 1.8 Ω-cm (one standard deviation). The
Typical plots of the raw data are shown in Figs. 2-4. No attempt
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 veri
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: G106 − 89 (Reapproved 2010) G106 − 89 (Reapproved 2015)
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. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. 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.
2. Referenced Documents
2.1 ASTM Standards:
D1193 Specification for Reagent Water
G3 Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing
G5 Reference Test Method for Making Potentiodynamic Anodic Polarization Measurements
G15 Terminology Relating to Corrosion and Corrosion Testing (Withdrawn 2010)
G59 Test Method for Conducting Potentiodynamic Polarization Resistance Measurements
3. Terminology
3.1 Definitions—For definitions of corrosion related terms, see Terminology G15.
3.2 Symbols:
−2
C = capacitance (farad-cm )
Eʹ = real component of voltage (volts)
E" = imaginary component of voltage (volts)
E = complex voltage (volts)
−1
f = frequency (s )
−2
Iʹ = real component of current (amp-cm )
−2
I" = imaginary component of current (amp-cm )
−2
I = complex current (amp-cm )
j =
=21
L = inductance (henry − cm )
R = solution resistance (ohm-cm )
s
R = polarization resistance (ohm-cm )
p
This practice is under the jurisdiction of ASTM Committee G01 on Corrosion of Metals and is the direct responsibility of Subcommittee G01.11 on Electrochemical
Measurements in Corrosion Testing.
Current edition approved May 1, 2010Nov. 1, 2015. Published May 2010December 2015. Originally approved in 1989. Last previous edition approved in 20042010 as
G106–89(2004).G106–89(2010). DOI: 10.1520/G0106-89R10.10.1520/G0106-89R15.
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 ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G106 − 89 (2015)
FIG. 1 Circuit Diagram for Dummy Cell Showing Positions for Hook-Up to Potentiostat
R = charge transfer resistance (ohm-cm )
t
Zʹ = real component of impedance (ohm-cm )
Z" = imaginary component of impedance (ohm-cm )
Z = complex impedance (ohm-cm )
α = phenomenological coefficients caused by depression of the Nyquist plot below the real axis, α is the exponent and τ is the
time constant(s).
θ = phase angle (deg)
−1
ω = frequency (radians-s )
3.3 Subscripts:
x = in-phase component
y = out-of-phase component
4. Summary of Practice
4.1 Reference impedance plots in both Nyquist and Bode format are included. These reference plots are derived from the results
from nine different laboratories that used a standard dummy cell and followed the standard procedure using a specific ferritic type
alloy UNS-S43000 in 0.005 M H SO and 0.495 M Na SO . The plots for the reference material are presented as an envelope
2 4 2 4
that surrounds all of the data with and without inclusion of the uncompensated resistance. Plots for one data set from one laboratory
are presented as well. Since the results from the dummy cell are independent of laboratory, only one set of results is presented.
4.2 A discussion of the electrochemical impedance technique, the physics that underlies it, and some methods of interpreting
the data are given in the Appendix X1 – Appendix X6. These sections are included to aid the individual in understanding the
electrochemical impedance technique and some of its capabilities. The information is not intended to be all inclusive.
5. Significance and Use
5.1 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.
5.2 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.
5.3 This test method may not be appropriate for electrochemical impedance measurements of all materials or in all
environments.
6. Apparatus
6.1 Dummy Cell—The dummy cell used to check the equipment and method for generating electrochemical impedance data is
composed of a 10 Ω precision resistor placed in series with a circuit element composed of a 100 Ω precision resistor in parallel
with a 100 μF capacitor. The resistors should have a stated precision of 60.1 %. The capacitor can have a precision of 620 %.
The cell can be constructed from readily available circuit elements by following the circuit diagram shown in Fig. 1.
These standard samples are available from ASTM Headquarters. Generally, one sample can be repolished and reused for many runs. This procedure is suggested to
conserve the available material.
G106 − 89 (2015)
6.2 Test Cell—The test cell should be constructed to allow the following items to be inserted into the solution chamber: the test
electrode, two counter electrodes or a symmetrically arranged counter electrode around the working electrode, a Luggin-Haber
capillary with salt bridge connection to the reference electrode, an inlet and an outlet for an inert gas, and a thermometer or
thermocouple holder. The test cell must be constructed of materials that will not corrode, deteriorate, or otherwise contaminate the
solution.
6.2.1 One type of suitable cell is described in Reference Test Method G5. Cells are not limited to that design. For example, a
1-L round-bottom flask can be modified for the addition of various necks to permit the introduction of electrodes, gas inlet and
outlet tubes, and the thermometer holder. A Luggin-Haber capillary probe could be used to separate the bulk solution from the
saturated calomel electrode. The capillary tip can be easily adjusted to bring it into close proximity to the working electrode. The
minimum distance should be no less than two capillary diameters from the working electrode.
6.3 Electrode Holder—The auxiliary and working electrodes can be mounted in the manner shown in Reference Test Method
G5. Precautions described in Reference Test Method G5 about assembly should be followed.
6.4 Potentiostat—The potentiostat must be of the kind that allows for the application of a potential sweep as described in
Reference Test Method G5 and Reference Practice G59. The potentiostat must have outputs in the form of voltage versus ground
for both potential and current. The potentiostat must have sufficient bandwidth for minimal phase shift up to at least 1000 Hz and
preferably to 10 000 Hz. The potentiostat must be capable of accepting an external excitation signal. Many commercial
potentiostats meet the specification requirements for these types of measurements.
6.5 Collection and Analysis of Current-Voltage Response—The potential and current measuring circuits must have the
characteristics described in Reference Test Method G5 along with sufficient band-width as described above. The impedance can
be calculated in several ways, for example, by means of a transfer function analyzer, Lissajous figures on an oscilloscope, or
transient analysis of a white noise input using a Fast Fourier Transform algorithm. Other methods of analysis exist.
6.6 Electrodes:
6.6.1 Working electrode preparation should follow Reference 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 Reference 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 a 10 Ω resistor in series with a parallel combination of a 100 Ω
resistor and a 100 μF capacitor. The circuit diagram is shown in Fig. 1.
7.1.2 Typical connections from the potentiostat are shown in Fig. 1. Connect the auxiliary electrode and reference electrode
leads to the series resistor side of the circuit. Connect the working electrode lead to the opposite side of the circuit beyond the
resistor-capacitor parallel combination.
7.1.3 Set the potential at 0.0V. 0.0 V. Collect the electrochemical impedance data between 10 000 Hz (10 kHz) and 0.1 Hz (100
mHz) (100 mHz) at 8 to 10 steps per frequency decade. The amplitude must be the same as that used to check the electrochemical
cell, 10 mV. The resulting frequency response when plotted in Nyquist format (the negative of the imaginary impedance versus
the real impedance) must agree with that shown in Figs. 2-4. Testing with the electrochemical cell should not be attempted until
that agreement is established. Results using the dummy circuit were found to be independent of laboratory.
7.2 Test of Electrochemical Cell:
7.2.1 Test specimens of the reference material should be prepared following the procedure described in Reference Test Method
G5. This procedure involves polishing the specimen with wet SiC paper with a final wet polish using 600 grit SiC paper prior to
the experiment. There should be a maximum delay of 1 h between final polishing and immersion in the test solution.
7.2.2 Prepare a 0.495 M Na SO solution containing 0.005 M H SO from reagent grade sulfuric acid and sodium sulfate and
2 4 2 4
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 at
a flow rate of about 100 to 150 cm /min. Continue the purge 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 instructions provided with
the potentiostat must be followed.
7.2.6 Record the open circuit potential, that is, the corrosion potential, for 1 h. The potential should be about −645 610 6 10
mV relative to the saturated calomel electrode. If the potential is more positive than −600 mV (SCE) then the specimen may have
G106 − 89 (2015)
FIG. 2 Nyquist Plot of Electrochemical Impedance Response for Dummy Cell
FIG. 3 Bode Plot, Impedance Magnitude Versus Frequency, of Electrochemical Impedance Response for Dummy Cell
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 Record the frequency response between 10 000 Hz (10 kHz) (10 kHz) and 0.1 Hz (100 mHz) at the corrosion potential
recorded after 1 h of exposure using 8 to 10 steps per frequency decade. The amplitude must be the same as that used in 7.1.3,
10 mV.
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 There was no attempt to estimate circuit analogues for the electrochemical impedance curves since there is no universally
recognized, standard method for making such estimates.
G106 − 89 (2015)
FIG. 4 Bode Plot, Phase Angle Versus Frequency, of Electrochemical Impedance Response for Dummy Cell
8. Standard Reference Results and Plots
8.1 Dummy Cell:
8.1.1 The results from nine different laboratories were virtually identical and overlaid each other almost perfectly. Typical plots
of the raw data are shown in Figs. 2-4. No attempt has been made to estimate the variance and standard deviation of the results
from the nine laboratories. The measured values of R , R , and the frequency at which the phase angle is a maximum must agree
s p
with these curves within the specifications of the instrumentation, resistors, and capacitors before testing of the electrochemical
cell commences. See 9.1.1.
8.2 Electrochemical Cell:
8.2.1 Standard electrochemical impedance plots in both Nyquist format and Bode format are shown in Figs. 5-7. These are
actual results from one laboratory. Figs. 8-10 show plots in both Nyquist and Bode formats which envelop all of the results from
the nine laboratories. The solution resista
...