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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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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First edition
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)
© 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
© ISO 2022 – All rights reserved

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ISO 3079:2022(E)
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This document was prepared by Technical Committee ISO/TC 156, Corrosion of metals and alloys.
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 © ISO 2022 – All rights reserved

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ISO 3079:2022(E)
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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