Is it critical to analyse the surface of the coupons after potentiodynamic testing or surface analysis after simple immersion testing is enough?
Dear Sana Mirza
it is enough to practiced the surface analysis after simple immersion testing by means of the different characterization techniques, since the immersion test is long term , reflecting the full kinetic of transient and steady state conditions of sample corrosion progress mechanisms.
Best regards
Dear Mohammed Hussein j. H. Al'Atia
Thank you for your answer. A quick follow up, I have done stainless steel immersion testing in seawater and found pitting corrosion after 30 days. To understand the corrosion behaviour, I ran some potentiodynamic polarization tests and recorded breakdown potential values. Is it critical to confirm the corrosion attack morphology from immersion testing with electrochemical testing?
Dear Dr. Sana Mirza ,
in general, you have 4 main different methods to study the corrosion behaviour of a specific material (protected or not by a coating or other surface treatments) in the environment of possible use:
1 - Field tests (according to standard regulations and followed by appropriate characterizations / evaluations) in a corrosive environment very similar to the one of use that require an exposure time of at least one year (or more);
2 - Salt spray chamber tests (these, too, according to standard regulations), conducted in a series of corrosive environments simulating those of real application, with often rapid assessments of a photographic type. These tests require an exposure time of about 1-2 months and are considered "accelerated tests";
3 - Lab tests in free corrosion conditions, in a controlled environment, followed by analysis of weight loss (gravimetric test)and / or morphological and chemical analyzes of the surface of the samples by scientific instrumements, for example Optical Microscopy, SEM, et. (time required about 1 month);
4 - Electrochemical measurements (eg. Potentiodynamic Polarization Curves, EIS, etc.) carried out in an suitable aggressive solution which, once the experimental parameters are optimized, are able to provide a comparative or absolute evaluation, in a time of order of one hour every single measure.
Now all that remains is to choose. Personally I prefer to use at least two of the tests mentioned above ... it is always better to have two results in agreement with each other, if time allows us to do this...
Best regards, Pierluigi Traverso
Dear Sana Mirza ,thank you for your kindly feedback.
Yes, it is critical since the morphology obtained from both test is totally different, but it is highly accepted if you refer to the electrochemical polarization test results as supportive results.
Best regards
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