ASTM G106-89(1999)
(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
SCOPE
1.1 This practice describes 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 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: G 106 – 89 (Reapproved 1999)
Standard Practice for
Verification of Algorithm and Equipment for Electrochemical
Impedance Measurements
This standard is issued under the fixed designation G 106; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope
E8 = real component of voltage (volts)
E9 = imaginary component of voltage (volts)
1.1 This practice describes an experimental procedure
E = complex voltage (volts)
which can be used to check one’s instrumentation and tech-
−1
f = frequency (s )
nique for collecting and presenting electrochemical impedance
−2
I8 = real component of current (amp-cm )
data. If followed, this practice provides a standard material,
−2
I9 = imaginary component of current (amp-cm )
electrolyte, and procedure for collecting electrochemical im-
−2
I = complex current (amp-cm )
pedance data at the open circuit or corrosion potential that
j = 21
=
should reproduce data determined by others at different times
L = inductance (henry − cm )
and in different laboratories. This practice may not be appro-
R = solution resistance (ohm-cm )
s
priate for collecting impedance information for all materials or
R = polarization resistance (ohm-cm )
p
in all environments.
R = charge transfer resistance (ohm-cm )
t
1.2 This standard does not purport to address all of the
Z8 = real component of impedance (ohm-cm )
safety concerns, if any, associated with its use. It is the Z9 = imaginary component of impedance (ohm-cm )
responsibility of the user of this standard to establish appro- Z = complex impedance (ohm-cm )
a = phenomenological coefficients caused by depression
priate safety and health practices and determine the applica-
of the Nyquist plot below the real axis, a is the
bility of regulatory limitations prior to use.
exponent and t is the time constant(s).
2. Referenced Documents
u = phase angle (deg)
−1
v = frequency (radians-s )
2.1 ASTM Standards:
D 1193 Specification for Reagent Water
Subscripts:
G 3 Practice for Conventions Applicable to Electrochemical
x = in-phase component
Measurements in Corrosion Testing
y = out-of-phase component
G 5 Reference Test Method for Making Potentiostatic and
Potentiodynamic Anodic Polarization Measurements
4. Summary of Practice
G 15 Terminology Relating to Corrosion and Corrosion
4.1 Reference impedance plots in both Nyquist and Bode
Testing
format are included. These reference plots are derived from the
G 59 Practice for Conducting Potentiodynamic Polarization
results from nine different laboratories that used a standard
Resistance Measurements
dummy cell and followed the standard procedure using a
specific ferritic type alloy UNS-S43000 in 0.005 M H SO
2 4
3. Terminology
and 0.495 M Na SO . The plots for the reference material are
2 4
3.1 Definitions—For definitions of corrosion related terms,
presented as an envelope that surrounds all of the data with and
see Terminology G 15.
without inclusion of the uncompensated resistance. Plots for
3.2 Symbols:
one data set from one laboratory are presented as well. Since
the results from the dummy cell are independent of laboratory,
−2
only one set of results is presented.
C = capacitance (farad-cm )
4.2 A discussion of the electrochemical impedance tech-
nique, the physics that underlies it, and some methods of
1 interpreting the data are given in the Appendix X1-Appendix
This practice is under the jurisdiction of ASTM Committee G-1 on Corrosion
of Metals and is the direct responsibility of Subcommittee G01.11 on Electrochemi-
cal Measurements in Corrosion Testing.
Current edition approved Sept. 29, 1989. Published November 1989.Originally
e1 4
published as G 106-89. Last previous edition G 106 - 89 (1994) . These standard samples are available from ASTM Headquarters. Generally, one
Annual Book of ASTM Standards, Vol 11.01. sample can be repolished and reused for many runs. This procedure is suggested to
Annual Book of ASTM Standards, Vol 03.02. conserve the available material. Order PCN 12–700050–00.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
G 106 – 89 (1999)
X6. These sections are included to aid the individual in electrode. The minimum distance should be no less than two
understanding the electrochemical impedance technique and capillary diameters from the working electrode.
some of its capabilities. The information is not intended to be
6.3 Electrode Holder—The auxillary and working elec-
all inclusive.
trodes can be mounted in the manner shown in Reference Test
Method G 5. Precautions described in Reference Test Method
5. Significance and Use
G 5 about assembly should be followed.
5.1 The availability of a standard procedure, standard ma-
6.4 Potentiostat—The potentiostat must be of the kind that
terial, and standard plots should allow the investigator to check
allows for the application of a potential sweep as described in
his laboratory technique. This practice should lead to electro-
Reference Test Method G 5 and Reference Practice G 59. The
chemical impedance curves in the literature which can be
potentiostat must have outputs in the form of voltage versus
compared easily and with confidence.
ground for both potential and current. The potentiostat must
5.2 Samples of a standard ferritic type 430 stainless steel
have sufficient bandwidth for minimal phase shift up to at least
(UNS 430000) used to obtain the reference plots are available
1000 Hz and preferably to 10 000 Hz. The potentiostat must be
for those who wish to check their equipment. Suitable resistors
capable of accepting an external excitation signal. Many
and capacitors can be obtained from electronics supply houses.
commercial potentiostats meet the specification requirements
5.3 This test method may not be appropriate for electro-
for these types of measurements.
chemical impedance measurements of all materials or in all
6.5 Collection and Analysis of Current-Voltage Response—
environments.
The potential and current measuring circuits must have the
characteristics described in Reference Test Method G 5 along
6. Apparatus
with sufficient band-width as described above. The impedance
6.1 Dummy Cell—The dummy cell used to check the
can be calculated in several ways, for example, by means of a
equipment and method for generating electrochemical imped-
transfer function analyzer, Lissajous figures on an oscilloscope,
ance data is composed of a 10 V precision resistor placed in
or transient analysis of a white noise input using a Fast Fourier
series with a circuit element composed of a 100 V precision
Transform algorithm. Other methods of analysis exist.
resistor in parallel with a 100 μF capacitor. The resistors should
6.6 Electrodes:
have a stated precision of 60.1 %. The capacitor can have a
6.6.1 Working electrode preparation should follow Refer-
precision of 620 %. The cell can be constructed from readily
ence Test Method G 5, which involves drilling and tapping the
available circuit elements by following the circuit diagram
specimen and mounting it on the electrode holder.
shown in Fig. 1.
6.6.2 Auxillary electrode preparation should follow Refer-
6.2 Test Cell—The test cell should be constructed to allow
ence Test Method G 5. The auxillary electrode arrangement
the following items to be inserted into the solution chamber:
should be symmetrical around the working electrode.
the test electrode, two counter electrodes or a symmetrically
6.6.3 Reference electrode type and usage should follow
arranged counter electrode around the working electrode, a
Reference Test Method G 5. The reference electrode is to be a
Luggin-Haber capillary with salt bridge connection to the
saturated calomel electrode.
reference electrode, an inlet and an outlet for an inert gas, and
a thermometer or thermocouple holder. The test cell must be
7. Experimental Procedure
constructed of materials that will not corrode, deteriorate, or
7.1 Test of Algorithm and Electronic Equipment (Dummy
otherwise contaminate the solution.
Cell):
6.2.1 One type of suitable cell is described in Reference Test
7.1.1 Measure the impedance of a dummy cell consisting of
Method G 5. Cells are not limited to that design. For example,
a10 V resistor in series with a parallel combination of a 100
a 1-L round-bottom flask can be modified for the addition of
V resistor and a 100 μF capacitor. The circuit diagram is shown
various necks to permit the introduction of electrodes, gas inlet
and outlet tubes, and the thermometer holder. A Luggin-Haber in Fig. 1.
capillary probe could be used to separate the bulk solution from 7.1.2 Typical connections from the potentiostat are shown in
the saturated calomel electrode. The capillary tip can be easily Fig. 1. Connect the auxillary electrode and reference electrode
adjusted to bring it into close proximity to the working leads to the series resistor side of the circuit. Connect the
FIG. 1 Circuit Diagram for Dummy Cell Showing Positions for Hook-Up to Potentiostat
G 106 – 89 (1999)
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. 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
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 G 5. 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
2 4
FIG. 3 Bode Plot, Impedance Magnitude Versus Frequency, of
MH SO from reagent grade sulfuric acid and sodium sulfate
2 4
Electrochemical Impedance Response for Dummy Cell
and Type IV reagent water described in Specification D 1193.
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.
FIG. 4 Bode Plot, Phase Angle Versus Frequency, of
Electrochemical Impedance Response for Dummy Cell
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
potential, for 1 h. The potential should be about −645 mv 610
mv 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
FIG. 2 Nyquist Plot of Electrochemical Impedance Response for
Dummy Cell 600 grit wet silicon carbide paper. Then reimmerse the sample
G 106 – 89 (1999)
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 after1hof exposure using 8 to 10 steps per frequency
decade. The amplitude must be the same as that used in 6.1.3,
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.
8. Standard Reference Results and Plots
8.1 Dummy Cell:
FIG. 6 Bode Plot, Impedance Magnitude Versus Frequency, for
8.1.1 The results from nine different laboratories were
UNS-S43000 From One Laboratory
virtually identical and overlayed 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
s p
maximum must agree with these curves within the specifica-
tions 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 resistance from each
laboratory was not subtracted out prior to making this plot.
8.2.2 The average solution resistance from the nine labora-
2 2
tories in 3.3 V-cm 6 1.8 V-cm (one standard deviation). The
solution resistance of the user’s test cell as measured by the
FIG. 7 Bode Plot, Phase Angle Versus Frequency, for UNS-
S43000 From One Laboratory
high frequency intercept on the Nyquist plot must lie in this
range to use agreement with Figs. 8-10 for verification of the
electrochemical test cell. If the uncompensated resistance lies
outside of this range, it should be subtracted from the results
(see 7.2.4). Then, results from the electrochemical test cell can
be compared with the results in Figs.
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