Organic Coatings (Paint)

Organic Coatings (Paint)

Good corrosion resistance is frequently a requirement of paint coatings. In addition to the structural damage which will result from under film corrosion, the highly visible nature of many applications, for example, car bodies, makes corrosion an aesthetic problem too.

Accelerated Environmental Techniques, such as neutral spray testing and humidity testing are widely recognised techniques for measuring the corrosion resistance of paint coatings. The duration of the tests is dependent on the coating, but may extend to 500 or 1000 hours. The tendency for a coating to delaminate at a scratch or cut edge can be assessed by simulating these occurrences prior to testing.

Impedance Spectroscopy is a useful tool for testing paints, as it can be used to measure water uptake, which typically precedes the corrosion of the substrate. Additionally, the technique can detect electrochemical (corrosion) activity occurring at the metal surface before it is detectable by eye. Data can be acquired after short periods, or samples can be subjected to longer exposure in a corrosive solution to monitor their deterioration.

Localised Corrosion Measurements can also be performed on paint coatings. Of these, the scanning vibrating electrode technique (SVET) can be used to obtain information about corrosion activity occurring when the coating becomes delaminated, for example at a cut edge. The scanning droplet cell (SDC) can also perform impedance experiments, using the same technique as for general impedance testing but with data acquired from a small area of the sample (around 1mm diameter). This allows specific points of interest on the surface of a coating to be examined.

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