Greetings everyone!
I've been struggling with this problem for quite a long time and have to admit that I need help.
The main task is to obtain pitting characteristics of 13Cr metal using different electrochemical techniques. I need to find a way to avoid crevice corrosion in electrochemical methods of determining pitting potentials. The sample surface was polished (2.5 μm diamond paste - mirror surface). A 3.5% NaCl solution with CO2 was used. Stirring.
What I have tried so far in order to avoid crevice corrosion is as follows:
1) I polished a cubic metal sample from all sides and connected it through a PTFE compression gasket for the sample holder rod (Gamry Ins. kit) - I observed crevice corrosion under the PTFE gasket on the metal surface.
2) I embedded the sample in just epoxy resin - I observed crevice corrosion at the interface between the metal surface and the epoxy resin.
3) I embedded the sample in epoxy resin and sealed the area of the specimen near the interface between the resin and the specimen with silica gel sealant - I observed crevice corrosion near the metal surface/silica gel sealant border.
4) I embedded the sample in epoxy resin and covered the area of the specimen near the interface between the resin and the specimen with insulating tape (3M™ Electroplating Tape 470!) - I observed crevice corrosion under the insulating tape near the metal surface/tape border.
5) I embedded the sample in epoxy resin and sealed the area of the specimen near the interface between the resin and the specimen with insulating varnish (see picture) - I observed crevice corrosion near the metal surface/varnish border.
I have also tried steps 2-5 without using epoxy resin, but still observed crevice corrosion near the non-metallic sealant or under it.
I am sure that this is not an issue with the electrochemical technique as I have tried different modes, different steels as well.
One thing I haven't tried yet is prepassivating the specimen surface in HNO3. Would this be helpful? Or would it alter the surface and affect the true electrochemical characteristics of pitting corrosion?
Any other advice would be greatly appreciated. Thank you for reading all of this.
Уважаемый исследователь. Чтобы избежать щелевой коррозии нужно полностью убрать границы "покрытие - металл". весь металл должен быть покрыт. Иначе, даже с пассивацией, вы получите щелевую коррозию.
Anatoly Laptev Спасибо за Ваш ответ. К сожалению, полное покрытие поверхности металла не представляется возможным, так как сам эксперимент заключается в исследовании этой поверхности. Возможно есть какие-то способы минимизировать щелевую коррозию на границе металл/покрытие?
Dear Ekaterina Mansurova, I recommend the following ways to avoid crevice corrosion: 1. Eliminate the irregularities on the surface that can trap corrosive agents. Smooth surfaces minimize the formation of crevices where corrosion can occur. 2. Employ corrosion inhibitors in the electrolyte or surrounding environment to mitigate the risk of crevice corrosion.
Dear Ekaterina Mansurova,
may I suggest you use the Avesta electrochemical cell, which was developed to avoid crevice during pitting corrosion testing (https://doi.org/10.1016/0010-938X(88)90090-X)
There are many versions on the market that can perhaps be adapted to the size of your samples.
Use a gelled electrolyte:Article Design of gel electrolytes for electrochemical studies on me...
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