Florida Research dry electrodes corrosion, reaction, discoloration

Aniol1349 · December 2016

Hey guys,

I'm about to complete my headset but I'm a bit scared to attach my electrodes. I read some users have experience corrosion even after one day when using them with stainless steel mounting.

Have any one experience this and are there any ways to avoid it?

Cheers!

wjcroft · December 2016

Aniol, hi.

If everything is dry you will not have any issues. The only posts here on the forum that I've seen regarding FRI electrode corrosion, have been when using the FRI clip-on cables plus the FRI electrodes in an environment where there is constant moisture involved around that cable / electrode connection. With the Ultracortex headset all of the connections are dry: electrode, screws, wires, etc.

Also mentioning Karl Zurn @kzurn at FRI.

Regards,

William

Aniol1349 · December 2016

Thank you for your answer William.

I'm gonna go ahead and finish the assembly.

Aniol1349 · December 2016

Unfortunately the electrodes start to corrode as soon as I attach them with the stainless steel bolts. Would it be possible to solder a wire directly to the electrode and then attach them using nylon bolts?

wjcroft · December 2016

Aniol, hi again.

Mentioning Karl @kzurn and @Conor . I have not heard of this issue before: "the electrodes start to corrode as soon as I attach them". Can you post a photo?

The electrodes are plastic with 2 platings: first silver, then the silver is chlorided. No, it is not possible to solder to something made out of plastic without melting the plastic. Is it possible that your anxiety about seeing some (rare) mention of FRI electrode corrosion, may be complicating the situation?

Even if you are seeing a slight discoloration for some reason, that may not be a sign of corrosion that would affect performance. The electrodes must be attached with the bolts as described.

I do wonder if some stainless bolts from certain manufacturers may contain certain alloy combinations that cause the effect you are seeing. Or if the bolts might have had some kind of oils or coatings related to what is happening.

William

wjcroft · December 2016

If the issue is caused by some type of oil or machining residue on the bolts, you could first try cleaning the bolts with solvent that evaporates well, such as alcohol or acetone.

Aniol1349 · December 2016

Thanks for your quick reply,

I didn't realise it was coated plastic, its not stated on the product page. Within two minutes from mounting the electrode to I noticed a small band of oxidation around the bolt, in the next 10 minutes it has grown and then I removed it to avoid any further damage.

I will try cleaning them with isopropyl alcohol and see if that helps.

I did a trial with copper wire wrapped around the electrode to see if copper causes the same effect and by now it seems its fine.

wjcroft · December 2016

This looks to be some kind of chemical reaction, not 'corrosion' per se. But nonetheless may be affecting the chloride coating. The silver plate may be just fine, which is what is important for the electrical contact with the screw. And the chemical change does not extend down to the scalp, where the chloride coating is still fine.

Thanks for the photos.

Would still appreciate insights from @kzurn and @Conor

Where did you get your stainless bolts?

Aniol1349 · December 2016

I got mines from eBay A2 Stainless Steel.

But I also read a post https://github.com/OpenBCI/Ultracortex/issues/21 which describes the same issue with the recommended parts.

wjcroft · December 2016

Thanks for that link to the Ultracortex issues page. The coloration pattern looks very similar with white band on the edge and brown / rusty color inside the white band.

If the isopropyl doesnt solve the issue, try other possibly stronger solvents.

Stainless alloys may contain various other elements such as nickel, chromium, manganese. One of these may be interacting with the silver / silver chloride. And may be a matter of luck what stock you get from the supplier.

https://en.wikipedia.org/wiki/Stainless_steel#Types

EVEN the user who submitted that issue page, if they "used the parts listed" for the Ultracortex build -- could have wound up with bolts or oil coating that trigger this. Mechanical part suppliers get stock from many vendors. And do not have the same kind of chemical purity you would get with chemical grades,

https://www.sciencecompany.com/Learn-Chemical-Grade-Definitions-from-Highest-to-Lowest-Purity..aspx

William

Aniol1349 · December 2016

Just a quick update, the electrodes did react with the stainless steel bolt however measuring with a DMM I didn't observe any significant loss in conductivity.

wjcroft · December 2016

So to clarify, you did not try cleaning off a new bolt, then using that with a new FRI electrode. As a test to see if it was the oil or coating on the bolts that was responsible, not the stainless steel itself reacting with the Ag-AgCl coating.

This would be a useful data point to arrive at a solution for others who have seen this issue.

Thanks,

Aniol1349 · December 2016

Yes I did try cleaning the bolt with isopropyl alcohol, however it didn't have any positive effect and the electrode was still reacting with it.

wjcroft · December 2016

https://www.google.com/search?q=do+alcohol+and+oil+mix

Alcohol is likely not the best cleaning agent for coatings applied during manufacturing.

https://www.google.com/search?q=best+solvent+to+remove+oil

Aniol1349 · December 2016

Ok so I cleaned the bolts with Servisol 10 which I normally use to clean potentiometers and switches and I always found it good to cleaning off any residue from electronics parts. I also tried cleaning them with hot water and washing up liquid which in theory should remove oil from the parts.

Unfortunately the problem remains, the discolouration is still present, I would say its even more aggressive than before. I will try another product but it is a little frustrating as it stops me in completing my headset.

I have measured the electrode and attached to the bolt and the resistance is very low so at least it seems like this discolouration doesn't affect the conductivity.

Regards,

Hubert

wjcroft · December 2016

Acetone is what you want. Servisol likely contains lubricants if it is recommended for contact cleaning. Water based methods are also not going to work.

Aniol1349 · December 2016

Thanks @wjcroft I will report back after I try it.

Aniol1349 · December 2016

Cleaned the bolts and nuts with acetone today, I have soaked them for a while then cleaned them with Q-tips, then towel dry them, and repeat once again.

The result however is the same, I attached the bolt to a new electrode, 5 mins and the reaction was already discolouring the electrode.

Is it possible the quality of the bolts is that bad and contaminated with impurities that there is no way to stop it from happening?

wjcroft · December 2016

Hubert, wow.

Thanks so much for all your solvent cleaning tests. It does now look like you have some kind of stainless steel alloy (as mentioned a few posts back) with a reactive element to the Ag-AgCl.

https://en.wikipedia.org/wiki/Stainless_steel#Types

William

davide_93 · October 2017

Hi all,

I'm experiencing a weird problem with the dry electrodes of my Mark III headset (which I built by myself).

The problem is the following one: some hours after inserting the dry electrodes in the electrode holders following the procedure described here, it is possible to notice a corrosion (?) of the electrodes. At this link you can see a picture showing the condition of the electrodes.

In the past, I have used these same electrodes with another Mark III headset that I built, and I didn't experience this problem at all (even after 100+ recordings). Does anybody have an idea of what is happening here? Could this problem be caused by the screw? Should I try to loosen the screw?

Thanks in advance,

Davide

wjcroft · October 2017

Davide, hi. I merged your question into this existing thread.

The corrosion seems to be related to the alloy type of the stainless screws. Did you use a different box of screws on the first Mark III?

William

davide_93 · October 2017

Hi William,

thanks for your reply.

Yes, for the first Mark III I used the McMaster-Carr screws that are suggested in the tutorial (I was in the US back then). For the second Mark III, I used another type of screws (I cannot buy from McMaster-Carr since I'm in Italy now). Do you have any suggestions for the screws that I should use?

Do you think that this phenomenon will influence the quality of the signal? Today in the lab I tested the impedance of the electrodes and, even if the electrodes were affected by this phenomenon, it seemed ok to me (in the range 5-30kOhm for the eight channels).

Thanks,

Davide

davide_93 · October 2017

A thing that I noticed today during my experiments is the following: leaving the electrode with the screw inserted and secured by the bolts didn't cause any "corrosion" up until the electrode is used for the first time for recording EEG (so, until current is flowing through the electrode).

wjcroft · October 2017

Davide, hi. My guess from the earlier posters on this thread, is that the corrosion will not affect your readings, since the actual parts / pins that touch the scalp are not affected.

Florida Research dry electrodes corrosion, reaction, discoloration

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