Two-electrode method using acetic acid to measure pitting potential of aluminium and aluminium alloys in chloride solutions

This document specifies a test method for the measurement of the pitting potential of aluminium and aluminium alloys in sodium chloride solution of a mass fraction of 5 %, with a fixed concentration of acetic acid as the oxidant, using a two-electrode system. This document provides a simple method for ranking aluminium alloys and is especially useful for evaluating galvanic protection performance of thin clad materials because the test method causes little specimen damage.

Méthode à deux électrodes utilisant l'acide acétique pour mesurer le potentiel de piqûre de l'aluminium et des alliages d'aluminium dans des solutions de chlorure

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Status
Published
Publication Date
13-Nov-2022
Current Stage
6060 - International Standard published
Due Date
07-Dec-2022
Completion Date
14-Nov-2022
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ISO 3079:2022 - Two-electrode method using acetic acid to measure pitting potential of aluminium and aluminium alloys in chloride solutions Released:14. 11. 2022
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INTERNATIONAL ISO
STANDARD 3079
First edition
2022-11
Two-electrode method using acetic
acid to measure pitting potential of
aluminium and aluminium alloys in
chloride solutions
Méthode à deux électrodes utilisant l'acide acétique pour mesurer le
potentiel de piqûre de l'aluminium et des alliages d'aluminium dans
des solutions de chlorure
Reference number
ISO 3079:2022(E)
© ISO 2022
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ISO 3079:2022(E)
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© ISO 2022

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© ISO 2022 – All rights reserved
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ISO 3079:2022(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction .................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Field of application ............................................................................................................................................................................................ 1

5 Comparison with conventional methods ................................................................................................................................... 1

5.1 Anodic polarization curve measurement ....................................................................................................................... 1

5.2 Corrosion potential............................................................................................................................................................................. 2

6 General principles .............................................................................................................................................................................................. 2

7 Apparatus .................................................................................................................................................................................................................... 3

7.1 Potentiometer .......................................................................................................................................................................................... 3

7.2 Working electrode ............................................................................................................................................................................... 3

7.3 Reference electrode ........................................................................................................................................................................... 3

7.4 Stirrer ............................................................................................................................................................................................................. 3

8 Specimen ...................................................................................................................................................................................................................... 4

9 Test procedure .......................................................................................................................................................................................................4

9.1 Solution ......................................................................................................................................................................................................... 4

9.2 Test set-up ................................................................................................................................................................................................... 5

9.3 Evaluation ................................................................................................................................................................................................... 6

10 Test report .................................................................................................................................................................................................................. 6

Bibliography ................................................................................................................................................................................................................................ 8

iii
© ISO 2022 – All rights reserved
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ISO 3079:2022(E)
Foreword

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bodies (ISO member bodies). The work of preparing International Standards is normally carried out

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electrotechnical standardization.

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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

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This document was prepared by Technical Committee ISO/TC 156, Corrosion of metals and alloys.

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.
© ISO 2022 – All rights reserved
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ISO 3079:2022(E)
Introduction

Aluminium and aluminium alloys show excellent corrosion resistance in near-neutral environments as

a result of the formation of an oxide or hydroxide film on their surface, thereby achieving passivation.

However, if the environment contains the chloride ion, the passive film will be broken, and localized

corrosion, such as pitting corrosion, can occur. Aluminium-clad material is used to prevent localized

corrosion by galvanic protection. In this method, the underlying core aluminium is protected by a

sacrificial layer whose pitting potential is lower than that of the core aluminium. Therefore, in order to

estimate the performance of galvanic protection, it is important to obtain the pitting potential.

Although anodic polarization curve measurement is one method for obtaining the pitting potential, the

method described in the test method in this document has several advantages in that it causes less

specimen damage, has a shorter measurement time and smaller specimen area, multiple measurements

are possible, and a two-electrode system is used. In an anodic polarization curve measurement, the

specimen is severely corroded due to excessive polarization. The method described in this document

causes less specimen corrosion, as the degree of polarization is small because the potential is maintained

near the pitting potential. This makes it possible to conduct repeated etching and measurements with

the same specimen, which is particularly useful for measurement of the depth profile of the pitting

potential in thin clad materials. As a method for measuring the corrosion potential of aluminium

alloys, ASTM G69 was established in 1997. ASTM G69 is widely used, substantially to obtain the pitting

potential without the anodic polarization curve measurement. In ASTM G69, 1 M (a mass fraction of

5,85 %) of sodium chloride is used as the solution and hydrogen peroxide is used as the oxidant. The

test method in this document, where a sodium chloride mass fraction of 5 % is used as the solution

and acetic acid is used as the oxidant, also has advantages over ASTM G69. In particular, it causes less

specimen damage and has a more stable oxidant with a buffer action.
© ISO 2022 – All rights reserved
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