Localised corrosion test techniques

Within the Centre for Corrosion Technology (CCT), facilities exist for conducting localised corrosion tests. These techniques have allowed researchers to examine specific phenomena related to corrosion degradation, such as organic coating delamination, stress corrosion cracking, pitting corrosion and repassivation. The range of equipment available includes a scanning vibrating electrode (SVET), scanning Kelvin probe (SKP) and scanning droplet cell (SDC).

The SVET is used to measure the corrosion of conducting materials immersed in an electrolyte. The surface of the corroding material consists of anodic and cathodic sites, resulting in potential gradients forming in the solution. These are measured by a microelectrode which is vibrated perpendicular to the sample surface, hence the name given to this technique. A simple calibration procedure can also allow the measured potentials to be converted to corrosion currents.

The SKP is a non contact technique which, unlike other electrochemical methods, does not require the specimen to be immersed in or exposed to a corrosive medium. Non-conducting materials are essntially transpareent to this technique so corrosion beneath paint coatings can ne characterised using this method.

The scanning droplet cell is not a technique, but is a piece of equipment that allows a full range of electrochemical tests to be performed within a small droplet of electrolyte, typically around 1 mm diameter. The electrolyte is constantly replenished, the solution being fed through a capillary arrangement, whereby the spent electrolyte is also removed.

SVET line scan of a scratched chrome-free passivate on a zinc electrodeposit. The scan shows corrosion activity at the scratch which diminishes with time.

External links

Further details of localised corrosion measurement techniques are available on the Electrochemical Scanning Probe Network (ESPNET) website

Equipment manufacturer Uniscan Instruments also have more information on their website.

Sheffield Hallam University is not responsible for the content of external websites

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