SIST-TP CEN ISO/TR 5602:2023
(Main)Sources of error in the use of electrochemical impedance spectroscopy for the investigation of coatings and other materials (ISO/TR 5602:2021)
Sources of error in the use of electrochemical impedance spectroscopy for the investigation of coatings and other materials (ISO/TR 5602:2021)
This document describes the main sources of error in the use of electrochemical impedance spectroscopy for the investigation of coatings and other materials. The sources of error listed here include all process steps from the set-up of the sample with the measuring cell right through to evaluation.
Fehlerquellen bei der Anwendung elektrochemischer Elektroimpdanzspektroskopie bei der Untersuchung von Beschichtungen und anderer Stoffe (ISO/TR 5602:2021)
Dieses Dokument beschreibt die wichtigsten Fehlerquellen bei der Anwendung der elektrochemischen Impedanzspektroskopie zur Untersuchung von Beschichtungen und anderen Materialien. Die hier aufgeführten Fehlerquellen umfassen alle Prozessschritte vom Probenaufbau mit der Messzelle bis hin zur Auswertung.
ANMERKUNG Die hier erörterten Fehlerquellen stellen keine vollständige Liste dar.
Sources d'erreur dans l'utilisation de la spectroscopie d’impédance électrochimique pour l'étude des revêtements et autres matériaux (ISO/TR 5602:2021)
Le présent document décrit les principales sources d’erreur dans l’utilisation de la spectroscopie d’impédance électrochimique pour l’étude des revêtements et autres matériaux. Les sources d’erreur énumérées ici comprennent toutes les étapes du processus, de la mise en place de l’échantillon avec la cellule de mesure jusqu’à l’évaluation.
NOTE Les sources d’erreur évoquées ici ne constituent pas une liste exhaustive.
Viri napak pri uporabi elektrokemijske impedančne spektroskopije pri preiskavah premazov in drugih materialov (ISO/TR 5602:2021)
Ta dokument opisuje glavne vire napak pri uporabi elektrokemijske impedančne spektroskopije pri preiskavah premazov in drugih materialov. Tukaj navedeni viri napak vključujejo vse korake postopka od nastavitve vzorca z merilno celico vse do ocene.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST-TP CEN ISO/TR 5602:2023
01-februar-2023
Viri napak pri uporabi elektrokemijske impedančne spektroskopije pri preiskavah
premazov in drugih materialov (ISO/TR 5602:2021)
Sources of error in the use of electrochemical impedance spectroscopy for the
investigation of coatings and other materials (ISO/TR 5602:2021)
Fehlerquellen bei der Anwendung elektrochemischer Elektroimpdanzspektroskopie bei
der Untersuchung von Beschichtungen und anderer Stoffe (ISO/TR 5602:2021)
Sources d'erreur dans l'utilisation de la spectroscopie d’impédance électrochimique pour
l'étude des revêtements et autres matériaux (ISO/TR 5602:2021)
Ta slovenski standard je istoveten z: CEN ISO/TR 5602:2022
ICS:
87.040 Barve in laki Paints and varnishes
SIST-TP CEN ISO/TR 5602:2023 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST-TP CEN ISO/TR 5602:2023
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SIST-TP CEN ISO/TR 5602:2023
CEN ISO/TR 5602
TECHNICAL REPORT
RAPPORT TECHNIQUE
November 2022
TECHNISCHER REPORT
ICS 87.040
English Version
Sources of error in the use of electrochemical impedance
spectroscopy for the investigation of coatings and other
materials (ISO/TR 5602:2021)
Sources d'erreur dans l'utilisation de la spectroscopie Fehlerquellen bei der Anwendung elektrochemischer
d'impédance électrochimique pour l'étude des Elektroimpdanzspektroskopie bei der Untersuchung
revêtements et autres matériaux (ISO/TR 5602:2021) von Beschichtungen und anderer Stoffe (ISO/TR
5602:2021)
This Technical Report was approved by CEN on 21 November 2022. It has been drawn up by the Technical Committee CEN/TC
139.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN ISO/TR 5602:2022 E
worldwide for CEN national Members.
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CEN ISO/TR 5602:2022 (E)
Contents Page
European foreword . 3
2
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SIST-TP CEN ISO/TR 5602:2023
CEN ISO/TR 5602:2022 (E)
European foreword
The text of ISO/TR 5602:2021 has been prepared by Technical Committee ISO/TC 35 "Paints and
varnishes” of the International Organization for Standardization (ISO) and has been taken over as
CEN ISO/TR 5602:2022 by Technical Committee CEN/TC 139 “Paints and varnishes” the secretariat of
which is held by DIN.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
Endorsement notice
The text of ISO/TR 5602:2021 has been approved by CEN as CEN ISO/TR 5602:2022 without any
modification.
3
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SIST-TP CEN ISO/TR 5602:2023
TECHNICAL ISO/TR
REPORT 5602
First edition
2021-11
Sources of error in the use of
electrochemical impedance
spectroscopy for the investigation of
coatings and other materials
Sources d'erreur dans l'utilisation de la spectroscopie d’impédance
électrochimique pour l'étude des revêtements et autres matériaux
Reference number
ISO/TR 5602:2021(E)
© ISO 2021
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SIST-TP CEN ISO/TR 5602:2023
ISO/TR 5602:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
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ISO/TR 5602:2021(E)
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Error in the make-up of the measuring cell . 1
4.1 Roughness of the surface . 1
4.2 O-ring — Considerations about the precise determination of the exposed area . 3
4.3 Faulty cell make-up . 7
4.3.1 Optically detectable leaks . 7
4.3.2 Optically non-detectable causes . 7
4.4 Reference electrodes . 9
4.4.1 General information on the distance between the reference and working
electrodes . 9
4.4.2 Shielding . 11
4.4.3 Air bubble in the reference electrode . 11
4.4.4 Poisoning of the reference electrode . 11
4.4.5 Bleeding of the reference electrode . 11
4.5 Counter electrodes . 11
4.5.1 Relative sizes . 11
4.5.2 Reactive counter electrodes . 11
4.6 Gas inclusions in the measuring cell . 11
5 Faults caused by electronics incl. shielding .12
5.1 Faraday cage .12
5.2 Extended cable (without active shielding) . 15
5.3 Cable breaks . 16
5.4 Contact resistances between metallic contacts and the working electrode/counter
electrode . 17
5.5 Inductivities . 18
5.6 Measurement range switching . 19
5.7 Scattering signals in power supply . 20
5.8 Insufficient signal-to-noise ratio . 22
5.9 Influence of peripheral devices . 22
6 Parameter selection, measurement range limits .24
6.1 Open-lead test. 24
6.2 Note on dummy cells – ISO 16773-3 . 24
6.3 Unsuitable amplitude . 24
6.4 Insufficient frequency range .26
6.5 Repetition rate for subsequent measurements . 27
7 Non-stationary measurement conditions .28
7.1 General .28
7.2 Temperature fluctuations . 29
7.3 Electrolytic conductivity . 31
7.4 Swelling . 31
7.5 Drifting OCP . 31
7.6 Corroding working electrode .33
7.7 Reactive counter electrodes . 33
7.8 Gas formation at the counter electrode . 33
8 Design and selection of equivalent circuit diagrams.34
8.1 Constant phase element .34
8.2 Multiple possibilities for the selection of equivalent circuits . 35
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8.3 Warburg impedance . 37
9 Significance of measurement values from equivalent circuits .37
9.1 Measurement uncertainty . . 37
9.2 Plausibility analysis .38
10 Interpretation of the measurement values of various coating systems .39
10.1 Pre-treatment . 39
10.2 Film thickness and measurement surface .40
10.3 Number of layers . 41
10.4 Conditioning. 45
10.5 Generic type of binder . . 45
11 Presentation of data .45
Annex A (informative) Calculation of the coating capacitance .48
Annex B (informative) Further information on the influence of the double-layer capacitance .49
Annex C (informative) Estimation of the order of magnitude of an apparent capacitance
caused by corrosion .50
Bibliography .52
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ISO/TR 5602:2021(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 35, Paints and varnishes, Subcommittee
SC 9, General test methods for paints and varnishes.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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Introduction
Electrochemical impedance spectroscopy is described in detail in ISO 16773-1 to ISO 16773-4. It
became apparent during use of these standards that sources of error and measurement artefacts that
lead to incorrect interpretations are not dealt with comprehensively. This document supplements the
ISO 16773 series of standards to deal with this issue.
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SIST-TP CEN ISO/TR 5602:2023
TECHNICAL REPORT ISO/TR 5602:2021(E)
Sources of error in the use of electrochemical impedance
spectroscopy for the investigation of coatings and other
materials
1 Scope
This document describes the main sources of error in the use of electrochemical impedance spectroscopy
for the investigation of coatings and other materials. The sources of error listed here include all process
steps from the set-up of the sample with the measuring cell right through to evaluation.
NOTE The sources of error discussed here do not represent a complete list.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 4618, Paints and varnishes — Terms and definitions
ISO 16773-1, Electrochemical impedance spectroscopy (EIS) on coated and uncoated metallic specimens —
Part 1: Terms and definitions
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4618, ISO 16773-1 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
limit impedance
minimum or maximum impedance that can be measured using the impedance spectrometer
3.2
limit frequency
minimum or maximum frequency that can be set on the impedance spectrometer
4 Error in the make-up of the measuring cell
4.1 Roughness of the surface
A wet and rough surface could conduct stray currents to a scratch or artificial defect, see Figure 1. This
could yield in a spectrum showing a much lower resistance than in reality. Examples of spectra are
shown in Figure 2.
1
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ISO/TR 5602:2021(E)
Key
1 without UV-irradiation
2 after UV-irradiation
PMMA tube
seal
coating
electrolyte
steel
Figure 1 — Conductive path from counter electrode to scratch due to surface roughness
The rough surface was measured on the unscratched area. Although the rough surface was dried with
a tissue, the residual amount of water was sufficient to produce a conductive path via the scratch to the
substrate. As result, the spectrum of the sample resulted in the incorrect identification of a defective
coating. After 2 h of continuous immersion in the cell, the surface outside the cell had dried and the
conductive path was interrupted, which resulted in a typical spectrum of an intact coating.
2
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ISO/TR 5602:2021(E)
Key
X frequency, f, in Hz
Y1 impedance, Z, in Ω
Y2 phase angle, φ, in degrees
2 h drying
wet
Figure 2 — EIS spectra of the initially wet coating and 2 h after drying
4.2 O-ring — Considerations about the precise determination of the exposed area
If an O-ring is used to seal the cell, the exposed area is smaller than the theoretically assumed area
because the O-ring will be compressed, and therefore, the exposed area will be reduced (see Figure 3).
a) Ideal situation, uncompressed
3
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ISO/TR 5602:2021(E)
b) Real situation, compressed
Key
R radius of the uncompressed O-ring
0
a difference in the radius of the O-ring due to compression
Figure 3 — Uncompressed and compressed O-ring
This behaviour can be visualized easily by using two transparent PMMA (poly methylene methacrylate)
plates which were compressed with 4 screws. The screws were gently tightened only by hand and
without any tools.
Figure 4 shows the set-up and Figure 5 and Figure 6 show the compressed O-rings of 1,2 cm and 5 cm
diameter, respectively.
Figure 4 — Compression of O-ring using 4 screws
4
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SIST-TP CEN ISO/TR 5602:2023
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Figure 5 — Compressed O-ring of 1,2 cm diameter
Figure 6 — Compressed O-ring of 5 cm diameter
The exposed area can be calculated as illustrated in Figure 7.
2
SR=π ·
00
a) O-ring not compressed — Contact surface of the specimen with testing solution
5
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ISO/TR 5602:2021(E)
2
SR=−π · a
()
10
b) O-ring compressed — Contact surface of the specimen with testing solution
2 2
ΔπSS=−SR=⋅ −⋅π Ra−
()
01 0 0
c) Reduction of contact surface of specimen due to O-ring compression
Key
S geometric area with the O-ring uncompressed
0
S exposed area with the O-ring compressed
1
ΔS difference S − S
0 1
R radius of the uncompressed O-ring
0
a difference of the radius of the O-ring due to compression
Figure 7 — Calculation of the exposed area
The error dS between exposed area S and geometric area S can be approximated depending on the
1 0
O-ring radius, R , and the measured contact, 2a, using Formula (1):
0
2
2 ⋅⋅aR ⋅ a
ΔS
0
d S =⋅ 100= ⋅ 100 (1)
2
S
R
0
0
Some examples for calculation of the error of the exposed area are shown in Table 1.
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ISO/TR 5602:2021(E)
Table 1 — Approximate error estimation of contact surface of specimens in corrosion cells
Geometric area
Difference in Exposed area
Radius of the with the O-ring
the radius of the with the O-ring Error of the
uncompressed uncompressed
O-ring due to compressed exposed area
O-ring (theoretical
compression (real surface)
surface)
R a R − a S S dS
0 0 0 1
2 2
mm mm mm mm mm %
6 0,8 5,2 113 85 25
12 0,8 11,2 452 394 13
24 0,8 23,2 1 809 1 690 7
30 0,8 29,2 2 826 2 677 5
6 1 5 113 79 31
12 1 11 452 380 16
24 1 23 1 809 1 661 8
30 1 29 2 826 2 641 7
6 1,25 4,75 113 71 37
12 1,25 10,75 452 363 20
24 1,25 22,75 1 809 1 625 10
30 1,25 28,75 2 826 2 595 8
4.3 Faulty cell make-up
4.3.1 Optically detectable leaks
Optically detectable leaks in the measuring cell are obvious and are not dealt with here.
4.3.2 Optically non-detectable causes
The behaviour shown in Figure 8 was observed in a non-reproducible manner for a very well-
documented coating (cathodic e-coat) that is in familiar use in measurement technology. This behaviour
occurred with varying amounts of pressure on the measuring cell at different locations on the same
test panels; however, a direct relationship was not detected.
If the behaviour shown in Figure 8 is observed in a measuring cell, the measuring cell is not suitable.
Generally, every measurement set-up is tested for errors with a familiar system before this measuring
cell is used on an unfamiliar system.
7
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a) Magnitude of impedance as a function of frequency
b) Phase angle as a function of frequency
Key
X logarithm of the frequency, log f, in Hz
2
Y1 logarithm of the modulus of the impedance, log |Z|, in Ω⋅cm
Y2 absolute value of the phase angle, φ, in degrees
wrong sealing
sealing correct
wrong sealing
sealing correct
Figure 8 — Possible influence of a faulty cell set-up
8
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ISO/TR 5602:2021(E)
4.4 Reference electrodes
4.4.1 General information on the distance between the reference and working electrodes
RE1, RE2 and RE3 as shown in Figure 9 are the various positions where the reference electrode RE can
be placed to measure the potential. At distances very close to the working electrode, the equipotential
lines are close together and small variations in the position of the reference electrode can lead to
large variations in the ohmic drop. This applies in particular to uncoated samples. In some cases, it
is preferable not to use a Luggin capillary, and instead to place the reference electrode far from the
working electrode and measure and compensate for the ohmic drop.
Key
1 working electrode (WE)
2 reference electrode 1 (RE 1)
3 reference electrode 2 (RE 2)
4 reference electrode 3 (RE 3)
5 equipotential lines
Figure 9 — Equipotential lines shown at close proximity to the working electrode
The influence of the reference electrode distance is negligible for measurements on coated (high-
resistance) samples. See Figure 10.
9
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ISO/TR 5602:2021(E)
a) Three |Z| curves are shown here that were recorded with different distances between the
reference electrode and working electrode. The distances to the coated substrate are 37 mm
(top), 15 mm (middle) and 2 mm (bottom).
b) Three phase angle curves are shown here that were recorded with different distances be-
tween the reference electrode and working electrode. The distances to the coated substrate are
37 mm (top), 15 mm (middle) and 2 mm (bottom).
Key
X1 frequency, f, in Hz
X2 frequency, f, in Hz
2
Y1 modulus of the impedance, |Z|, in Ω⋅cm
Y2 absolute value of the phase angle, φ, degrees
top (mostly invisible due to overlayings with the middle and bottom data points)
middle
bottom
Figure 10 — Spe
...
SLOVENSKI STANDARD
kSIST-TP FprCEN ISO/TR 5602:2022
01-september-2022
Viri napak pri uporabi elektrokemijske impedančne spektroskopije pri preiskavah
premazov in drugih snovi (ISO/TR 5602:2021)
Sources of error in the use of electrochemical impedance spectroscopy for the
investigation of coatings and other materials (ISO/TR 5602:2021)
Fehlerquellen bei der Anwendung elektrochemischer Elektroimpdanzspektroskopie bei
der Untersuchung von Beschichtungen und anderer Stoffe (ISO/TR 5602:2021)
Sources d'erreur dans l'utilisation de la spectroscopie d’impédance électrochimique pour
l'étude des revêtements et autres matériaux (ISO/TR 5602:2021)
Ta slovenski standard je istoveten z: FprCEN ISO/TR 5602
ICS:
87.040 Barve in laki Paints and varnishes
kSIST-TP FprCEN ISO/TR 5602:2022 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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kSIST-TP FprCEN ISO/TR 5602:2022
TECHNICAL ISO/TR
REPORT 5602
First edition
2021-11
Sources of error in the use of
electrochemical impedance
spectroscopy for the investigation of
coatings and other materials
Sources d'erreur dans l'utilisation de la spectroscopie d’impédance
électrochimique pour l'étude des revêtements et autres matériaux
Reference number
ISO/TR 5602:2021(E)
© ISO 2021
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kSIST-TP FprCEN ISO/TR 5602:2022
ISO/TR 5602:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
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kSIST-TP FprCEN ISO/TR 5602:2022
ISO/TR 5602:2021(E)
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Error in the make-up of the measuring cell . 1
4.1 Roughness of the surface . 1
4.2 O-ring — Considerations about the precise determination of the exposed area . 3
4.3 Faulty cell make-up . 7
4.3.1 Optically detectable leaks . 7
4.3.2 Optically non-detectable causes . 7
4.4 Reference electrodes . 9
4.4.1 General information on the distance between the reference and working
electrodes . 9
4.4.2 Shielding . 11
4.4.3 Air bubble in the reference electrode . 11
4.4.4 Poisoning of the reference electrode . 11
4.4.5 Bleeding of the reference electrode . 11
4.5 Counter electrodes . 11
4.5.1 Relative sizes . 11
4.5.2 Reactive counter electrodes . 11
4.6 Gas inclusions in the measuring cell . 11
5 Faults caused by electronics incl. shielding .12
5.1 Faraday cage .12
5.2 Extended cable (without active shielding) . 15
5.3 Cable breaks . 16
5.4 Contact resistances between metallic contacts and the working electrode/counter
electrode . 17
5.5 Inductivities . 18
5.6 Measurement range switching . 19
5.7 Scattering signals in power supply . 20
5.8 Insufficient signal-to-noise ratio . 22
5.9 Influence of peripheral devices . 22
6 Parameter selection, measurement range limits .24
6.1 Open-lead test. 24
6.2 Note on dummy cells – ISO 16773-3 . 24
6.3 Unsuitable amplitude . 24
6.4 Insufficient frequency range .26
6.5 Repetition rate for subsequent measurements . 27
7 Non-stationary measurement conditions .28
7.1 General .28
7.2 Temperature fluctuations . 29
7.3 Electrolytic conductivity . 31
7.4 Swelling . 31
7.5 Drifting OCP . 31
7.6 Corroding working electrode .33
7.7 Reactive counter electrodes . 33
7.8 Gas formation at the counter electrode . 33
8 Design and selection of equivalent circuit diagrams.34
8.1 Constant phase element .34
8.2 Multiple possibilities for the selection of equivalent circuits . 35
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ISO/TR 5602:2021(E)
8.3 Warburg impedance . 37
9 Significance of measurement values from equivalent circuits .37
9.1 Measurement uncertainty . . 37
9.2 Plausibility analysis .38
10 Interpretation of the measurement values of various coating systems .39
10.1 Pre-treatment . 39
10.2 Film thickness and measurement surface .40
10.3 Number of layers . 41
10.4 Conditioning. 45
10.5 Generic type of binder . . 45
11 Presentation of data .45
Annex A (informative) Calculation of the coating capacitance .48
Annex B (informative) Further information on the influence of the double-layer capacitance .49
Annex C (informative) Estimation of the order of magnitude of an apparent capacitance
caused by corrosion .50
Bibliography .52
iv
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kSIST-TP FprCEN ISO/TR 5602:2022
ISO/TR 5602:2021(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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SC 9, General test methods for paints and varnishes.
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Introduction
Electrochemical impedance spectroscopy is described in detail in ISO 16773-1 to ISO 16773-4. It
became apparent during use of these standards that sources of error and measurement artefacts that
lead to incorrect interpretations are not dealt with comprehensively. This document supplements the
ISO 16773 series of standards to deal with this issue.
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TECHNICAL REPORT ISO/TR 5602:2021(E)
Sources of error in the use of electrochemical impedance
spectroscopy for the investigation of coatings and other
materials
1 Scope
This document describes the main sources of error in the use of electrochemical impedance spectroscopy
for the investigation of coatings and other materials. The sources of error listed here include all process
steps from the set-up of the sample with the measuring cell right through to evaluation.
NOTE The sources of error discussed here do not represent a complete list.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 4618, Paints and varnishes — Terms and definitions
ISO 16773-1, Electrochemical impedance spectroscopy (EIS) on coated and uncoated metallic specimens —
Part 1: Terms and definitions
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4618, ISO 16773-1 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
limit impedance
minimum or maximum impedance that can be measured using the impedance spectrometer
3.2
limit frequency
minimum or maximum frequency that can be set on the impedance spectrometer
4 Error in the make-up of the measuring cell
4.1 Roughness of the surface
A wet and rough surface could conduct stray currents to a scratch or artificial defect, see Figure 1. This
could yield in a spectrum showing a much lower resistance than in reality. Examples of spectra are
shown in Figure 2.
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Key
1 without UV-irradiation
2 after UV-irradiation
PMMA tube
seal
coating
electrolyte
steel
Figure 1 — Conductive path from counter electrode to scratch due to surface roughness
The rough surface was measured on the unscratched area. Although the rough surface was dried with
a tissue, the residual amount of water was sufficient to produce a conductive path via the scratch to the
substrate. As result, the spectrum of the sample resulted in the incorrect identification of a defective
coating. After 2 h of continuous immersion in the cell, the surface outside the cell had dried and the
conductive path was interrupted, which resulted in a typical spectrum of an intact coating.
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Key
X frequency, f, in Hz
Y1 impedance, Z, in Ω
Y2 phase angle, φ, in degrees
2 h drying
wet
Figure 2 — EIS spectra of the initially wet coating and 2 h after drying
4.2 O-ring — Considerations about the precise determination of the exposed area
If an O-ring is used to seal the cell, the exposed area is smaller than the theoretically assumed area
because the O-ring will be compressed, and therefore, the exposed area will be reduced (see Figure 3).
a) Ideal situation, uncompressed
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b) Real situation, compressed
Key
R radius of the uncompressed O-ring
0
a difference in the radius of the O-ring due to compression
Figure 3 — Uncompressed and compressed O-ring
This behaviour can be visualized easily by using two transparent PMMA (poly methylene methacrylate)
plates which were compressed with 4 screws. The screws were gently tightened only by hand and
without any tools.
Figure 4 shows the set-up and Figure 5 and Figure 6 show the compressed O-rings of 1,2 cm and 5 cm
diameter, respectively.
Figure 4 — Compression of O-ring using 4 screws
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Figure 5 — Compressed O-ring of 1,2 cm diameter
Figure 6 — Compressed O-ring of 5 cm diameter
The exposed area can be calculated as illustrated in Figure 7.
2
SR=π ·
00
a) O-ring not compressed — Contact surface of the specimen with testing solution
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2
SR=−π · a
()
10
b) O-ring compressed — Contact surface of the specimen with testing solution
2 2
ΔπSS=−SR=⋅ −⋅π Ra−
()
01 0 0
c) Reduction of contact surface of specimen due to O-ring compression
Key
S geometric area with the O-ring uncompressed
0
S exposed area with the O-ring compressed
1
ΔS difference S − S
0 1
R radius of the uncompressed O-ring
0
a difference of the radius of the O-ring due to compression
Figure 7 — Calculation of the exposed area
The error dS between exposed area S and geometric area S can be approximated depending on the
1 0
O-ring radius, R , and the measured contact, 2a, using Formula (1):
0
2
2 ⋅⋅aR ⋅ a
ΔS
0
d S =⋅ 100= ⋅ 100 (1)
2
S
R
0
0
Some examples for calculation of the error of the exposed area are shown in Table 1.
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Table 1 — Approximate error estimation of contact surface of specimens in corrosion cells
Geometric area
Difference in Exposed area
Radius of the with the O-ring
the radius of the with the O-ring Error of the
uncompressed uncompressed
O-ring due to compressed exposed area
O-ring (theoretical
compression (real surface)
surface)
R a R − a S S dS
0 0 0 1
2 2
mm mm mm mm mm %
6 0,8 5,2 113 85 25
12 0,8 11,2 452 394 13
24 0,8 23,2 1 809 1 690 7
30 0,8 29,2 2 826 2 677 5
6 1 5 113 79 31
12 1 11 452 380 16
24 1 23 1 809 1 661 8
30 1 29 2 826 2 641 7
6 1,25 4,75 113 71 37
12 1,25 10,75 452 363 20
24 1,25 22,75 1 809 1 625 10
30 1,25 28,75 2 826 2 595 8
4.3 Faulty cell make-up
4.3.1 Optically detectable leaks
Optically detectable leaks in the measuring cell are obvious and are not dealt with here.
4.3.2 Optically non-detectable causes
The behaviour shown in Figure 8 was observed in a non-reproducible manner for a very well-
documented coating (cathodic e-coat) that is in familiar use in measurement technology. This behaviour
occurred with varying amounts of pressure on the measuring cell at different locations on the same
test panels; however, a direct relationship was not detected.
If the behaviour shown in Figure 8 is observed in a measuring cell, the measuring cell is not suitable.
Generally, every measurement set-up is tested for errors with a familiar system before this measuring
cell is used on an unfamiliar system.
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a) Magnitude of impedance as a function of frequency
b) Phase angle as a function of frequency
Key
X logarithm of the frequency, log f, in Hz
2
Y1 logarithm of the modulus of the impedance, log |Z|, in Ω⋅cm
Y2 absolute value of the phase angle, φ, in degrees
wrong sealing
sealing correct
wrong sealing
sealing correct
Figure 8 — Possible influence of a faulty cell set-up
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4.4 Reference electrodes
4.4.1 General information on the distance between the reference and working electrodes
RE1, RE2 and RE3 as shown in Figure 9 are the various positions where the reference electrode RE can
be placed to measure the potential. At distances very close to the working electrode, the equipotential
lines are close together and small variations in the position of the reference electrode can lead to
large variations in the ohmic drop. This applies in particular to uncoated samples. In some cases, it
is preferable not to use a Luggin capillary, and instead to place the reference electrode far from the
working electrode and measure and compensate for the ohmic drop.
Key
1 working electrode (WE)
2 reference electrode 1 (RE 1)
3 reference electrode 2 (RE 2)
4 reference electrode 3 (RE 3)
5 equipotential lines
Figure 9 — Equipotential lines shown at close proximity to the working electrode
The influence of the reference electrode distance is negligible for measurements on coated (high-
resistance) samples. See Figure 10.
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a) Three |Z| curves are shown here that were recorded with different distances between the
reference electrode and working electrode. The distances to the coated substrate are 37 mm
(top), 15 mm (middle) and 2 mm (bottom).
b) Three phase angle curves are shown here that were recorded with different distances be-
tween the reference electrode and working electrode. The distances to the coated substrate are
37 mm (top), 15 mm (middle) and 2 mm (bottom).
Key
X1 frequency, f, in Hz
X2 frequency, f, in Hz
2
Y1 modulus of the impedance, |Z|, in Ω⋅cm
Y2 absolute value of the phase angle, φ, degrees
top (mostly invisible due to overlayings with the middle and bottom data points)
middle
bottom
Figure 10 — Spectra of coated (high-resistance) samples
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4.4.2 Shielding
If the distance between the reference electrode and working electrode is too small, the electrical field
is shielded, and this leads to an undefined state. Shielding of the working electrode by the reference
electrode can only occur as a problem with the Haber-Luggin capillary, as there is a very small distance
between the capillary opening and working electrode in this case.
4.4.3 Air bubble in the reference electrode
An air bubble in the reference electrode leads to undefined potentials and can result in strong
oscillations in the phase.
4.4.4 Poisoning of the reference electrode
Poisoning of the reference electrode occurs when ions or molecules diffuse into the electrode and react
with the reference material. This results in a potential shift. This effect is less significant with a coated
electrode than with a metallic electrode.
Poisoning of the reference electrode can largely be prevented by hydrostatic effects and by correctly
positioning the electrode.
The use of a Haber-Luggin electrode can be effective in order to delay poisoning of the reference
electrode.
4.4.5 Bleeding of the reference electrode
Diffusion of ions from the reference electrode into the electrolyte is referred to as bleeding of the
reference electrode. These ions can alter the reaction at the working electrode.
The use of a Haber-Luggin electrode can be effective in order to delay bleeding of the reference
electrode.
4.5 Counter electrodes
4.5.1 Relative sizes
For coated samples, there are no known artefacts that can be ascribed to an unsuitable choice of relative
sizes of the working electrode and counter electrode. This can be explained by the very low currents
in the measurement of these high-resistance systems. However, the area of the counter electrode is
chosen as large as possible.
4.5.2 Reactive counter electrodes
As regards the make-up of measuring cells, the counter electrode consists of a material that is inert to
the electrolyte over the period of measurement. If there are doubts as to the suitability of the counter
electrode material, comparative measurements are carried out on different materials with a known
reference sample. Exposure experiments are also carried out.
4.6 Gas inclusions in the measuring cell
Despite the influence of gas bubbles in the measuring cell that is to be expected theoretically, this could
not be verified in a test experiment with gas bubbles on the counter electrode, see Figure 11. A single-
layer test coating was measured.
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