Dear Murali,

I believe that the EIS measurements are the best assays that you can perform in your samples, because EIS is a non-destructive method and you can follow the degradation of your system during a long times in the same region. Furthermore, you can model the equivalent circuits, that improve your understand about your electrochemical system.

The polarization tests are destructive test and high resistive coatings could not be evaluated by this method.

The SSC tests may not be trusted, due the results obtained do not present a good correlation with the real results.

Best regards.

Dear Murali

All methods are good, if you want a non-destructive EIS method, but it is a method that will not give you much information; If you want to make the test more real and see how your material degrades in time if there is passivation and pittings, it is better potentiodynamic polarization and also the method of electrochemical noise you can observe if your material is passivatig  and if there are tendency to pittings. If a passive layer is formed and what type it is, if the corrosion products are released.

Electrochemical impedance spectroscopy offers an excellent and non-destructive means to do what u desire. EIS complemented with SEM/EDAX can provide u with the corrosion information such a effect of long term corrosion on surface morphology changes of the substrate, occurrence of pitting corrosion on the substrate as well as the elemental composition of the corrosion product layer formed on the substrate during the long term immersion test.

The EIS is an excellent choice for coated sample.   I have used with my co-worker the EIS to Monitor the Marine Bio-fouling of Different Alloys Exposed to Continuous Flowing Fresh Seawater for a duration of 180 days.

Refer to the following:

K. Al-Muhanna, K. Habib, Marine Bio-fouling of Different Alloys Exposed to Continuous Flowing Fresh Seawater by Electrochemical Impedance Spectroscopy, Journal of  Saudi Chemical Society (2012),doi: http://dx.doi.org/10.1016/j.jscs.2012.07.008.

Hi Murali,

relating any accelerated lab based test to real world performance is tricky. industry tend to use the salt spray and accelerated UV exposure (QUVA or QUVB, or even EMMAQUA) but relating these results to in life performance is not an exact science and is generally based on iterative knowledge (ie this formulation lasted x hours in salt spray and we have data over y years in use, so if formulation B lasts X+Z hours in salt spray then it should at least outlast y years. As pointed out, this correlation is not with out issues as the high salinity can cause corrosion products or processes that are not seen in the 'wild' (or not seen to that extent) - other tests such as eis etc require full immersion and this is often not the use that the material is for, so a wet / dry cycle better represents its use. EIS supplies one part of the puzzle, along with other electrochemical techniques, CV, OCP etc. SVET, SKP and timelapse microscopy can also be used to identify where on a sample corrosion occurs and help elucidate the mechanisms involved, but with the possible exception of timelapse microscopy i wouldn't class them as simple)

Dont forget that corrosion of a coated sample is not the only potential failure mode, (assuming it is a polymer coated sample) as UV plays a part in coating degradation which can affect porosity and performance as a barrier coating and hence affect the overall corrosion resistance. the link explores this in a relatively simple way.

hope this helps

Justin

Article The Use of 3D-SVET for the Examination of Plasticized PVC Co...

EIS because of non-destructive character. 

Hi Murali,

I have carried out for my research the 3 testing methods you mentioned above (NSS, EIS and polarisation). In my case, I just used NSS as a quick screening method since it can't be trusted to correlate to real environment and I was using EIS and polarisation as more reliable techniques. As it has been already mentioned, polarisation is a destructive technique and EIS is a non-destructive technique and you can gather lot of information with it although it is quite complicated and you will need to understand the mechanisms behind it.

As with all type of available tests, it will depend on your coating and the environment you would like to test it.

Kind regards,

Laura

https://doi.org/10.1016/j.surfcoat.2017.05.063

Thanks to all researchers for taking time from their tight schedule in answering my doubts. 

Hi there,

impedance measurements allow a comparison of the charge transfer/diffusion response of a Nyquist curve that provide a reasonable indication of the effectiveness of an inhibitor, together with some indication of the likely mechanism of protection.  The result is not perfect, but comparisons of inhibitor performance are easier to achieve and the findings are more clearly evident.

Initially you can check bu immersion studies and after EIS is best technique

Dear all, usually such information id possible via ' accelerated corrosion tests for coatings ', many available procedures and standard norms are available via simple search. My Regards

Hi there

you can try Potentiodynamic polarization but you need to use potentiostate device

or using the weight loss method it is simple but needs a long period of time.