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Corrosion in close-up
Rapid examination methods can shorten coating development times
Korrosion in Nahaufnahme - Schnelle Untersuchungsmethoden können die Entwicklungszeiten von Beschichtungen verkürzen
One of the most critical factors controlling the speed of development of new coatings is the duration of environmental testing. It is shown that rapid indications of corrosion resistance can be obtained from microscopic inspection, ion permeability and electrochemical noise measurements. However, all require some knowledge of the actual corrosion mechanisms to allow correlation with the performance of coatings in service. Three tests which give rapid indications of corrosion resistance are considered. Corrosion defects start long before they become large enough to be visible, so various forms of microscopy allow earlier detection - but the smaller the scale and the earlier the detection, the worse may be the correlation to actual performance. Ion permeability on free paint films is shown to correlate with the degree of blistering in a salt spray test. Measurement of electrochemical noise gives rapid indications of the extent of activation and leaching of anticorrosive pigments.However, all these methods require knowledge of the relevant corrosion mechanisms if they are to be correlated usefully with coating performance in service.
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