Could you post the curves and tell more about substrate and solution used?

As you specify that your coating behave in a different manner.....the ICorr 10^-8 is lower than 10^-7. which tells that the corrosion current is reduced by your specific coating.... hence the corrosion rate is reduced..... it may 2-4 times reduced .... which can be calculated by seeing your tafel plot.....

now come to your Ecorr value ... as the Ecorr value is reduced from 0.7V to 0.5 V hence in case of your coating the corrosion start at lower potential than the uncoated material.

Dear All thanks for the answer, this morning I went to lab and recheck the results. So there's one plot that better describe the findings. Sorry if it's not "ready to be published" it's just preliminary. The coated sample is the green one as you can see I've a change in Ecorr from 07 to 0.5 but a Icorr from 10-8 TO 10-7 (sorry for bad explaining in first question) .

What i feel dear ...... your have maintained wrongly the I corr and Ecorr values here....

If you compare the plot then, i could see that the green (coated) one shows the corrosion at higher potential then the red and black curves.....the potential is in negative scale so your coated material Ecorr is ~ (-0.6V) then red ~ (-0.7V) as (-0.6V ) is greater then (-0.7V) hence your coated sample will corroded at higher potential then uncoated one.

now if you come to Icorr values ... it seem that the the green one shows the 10^-4 which is not improved (worst) then the uncoated material.

one more point i am concluding here that your coated material is continuously corroded then the uncoated material whereas your uncoated material shows passivity after certain potential ... as some of the passive layer has been formed which protect it from further corrosion.

I think the most common methods to study the coatings(qualitatively) are (a) Polarization resistance(Rp) and (b) Electrochemical Impedance Spectroscopy(EIS), and futher you can also compare the Rp values that you have got from both methods.

thanks for the answer I will try to figure out even if the EIs measurements performed gave quite odd results.

Dear Mahanty- you explained the curves nicely- as you said that the uncoated samples show better passivity than the coated one, I think you are talking about the horizontal part of right side of the red and black curves, am i right ? secondly what does the left side these curves tell about corrosion? thanks

Do you mean the peak you can see in the plots ? (green coated samples and other colors two reference metals ?)

more detail about the coating. it is a silano trymetilsiloxysilane with carbon nanotubes. It is sprayes and it give to the surface a CA of 175°. The substrate is Al6082 (as is). when I put the solution in the cell I can see a bit of bubbles and the coating after the analysis is degraded (it seems the silicate part agregate). I hope this can help in giving more hint about the results

Super-hydrophobic coatings are good as a corrosion inhibitor coating when water is the target corrosive culprit. Thus Mg alloys are covered with superhydrophobic coating to prevent corrosion of Mg by water according to

Mg +2 H2O -------- Mg(OH)2 +H2( gas bubbles)

What was the corrosive solution used in your study?

used NaCl 0.5% and NaCl 0.05% water solution

Hello Giorgio. I had the similar results using films of poly(pirrole) on aluminium.....Do you find an explanation for your results?? Thanks

Hello and sorry for the late reply. We finded an explaination, pls send me a message for a longer answer + paper we pubblished. Sorry again for not answering before !

Origin has specific script that can help you in calculating them.  Also there are some free software that can help you in that. I suggest you to open a new question on the topic.