Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Creating Durable Ag/AgCl Wire and Electrodes
Q. Hello, my name is Pirouz Shamszad. I am an undergraduate physics major here at GWU. I am currently doing a joint research program with the medical school and I am experiencing a slight problem. I expect that this question is going to be a cinch for you guys to answer, but I say its dumber not to ask!
I need to create a silver-silver chloride wire. The electrodeposition process I am using now is not satisfactory. I do not get a thick enough coating nor do I get any durability. What method do you suggest in order to create a better Ag/AgCl electrode? Right now I am running 30 mA through a 2M HCl solution. I treat the silver wire in 3M HNO3 first. I do reverse polarity twice while I am depositing giving about 2 mins per run (in each direction) --> Is this even the correct way of doing it?
Thank you for your help and time. Also, if you can refer me to any good literature, I would appreciate it. Thank you.
(I have done extensive research on this so give me everything ya got! :) )
Pirouz Shamszad,Presidential Scholar -- PhysicsThe George Washington University, Washington, DC
1999
A. Hi, Pirouz.
Sorry, I don't know much about Silver / silver chloride cells, only metal finishing, so I can't help you except in terms of your plating and electrodeposition questions.
It sounds like you attempt to clean and activate the silver wire by immersion in nitric acid, and then try to electroplate more silver onto the wire from a silver chloride - hydrochloric acid solution?
The only reliable way to electroplate silver that I know of is from a silver cyanide plating solution, but I'm not sure that that is what you are even trying to do. Thanks for any available clarification.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
1999
A. I finally dug this out for you - I make my own Ag/AgCl reference electrodes sometimes.
Pre-age the silver wire (which must be 99.99% pure Ag) in a silver nitrate solution acidified with a little nitric acid. Then with it as the anode, and a platinum wire as the cathode, plate it in 1 M HCl. Use a current density of 5 - 10 mA/cm2. After a good coating is obtained, age the electrode overnight in distilled water.
You do not say what size wire you are using but I suspect the problem is that you current density is too high.
(This procedure is from "Experiments in Physical Chemistry" by Shoemaker, Garland, et al, McGraw Hill, 1981. It's a handy book for lab stuff like this.)
Dave Wichern
Consultant - The Bronx, New York
1999
Q. Dear Mr.,
I'm studying in Padjadjaran University. I have to finish my experiment about Ag-AgCl Electrode, but I have some trouble:
1. I don't have procedure for electroplating AgCl.
2. And how to connect the electrode to the wire.
I hope you can give me some information about my problems. Thank you.
Lika Pita Saristudent - Bandung, West Java, Indonesia
2003
A. The Ag-Cl is not electroplated. It is a solution.
Check with your chemistry department and see if anyone has a textbook on instrumental analysis. It is a little too deep to go over in a letter.
Have you been introduced to the Nernst Equation?
You may be able to find some information in the literature that comes with a pH probe.
- Navarre, Florida
2003
Q. Hi
Silver wire electrode pretreatment. Can you suggest the best method for pretreating pure silver wire to be used as a reference electrode in non-aqueous systems?
researcher - Singapore
2006
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Ed. note: As you see, we appended your inquiry to a thread which hopefully answers it. But get back to us if you have additional questions.
A. Hi, I have tried the 1 M solution technique advised above a few times. Here's my tips.
1) abrade the wire with very fine sandpaper
2) nitric acid - not too strong. Dilute at least 10 to 1 from fuming
3) rinse in distilled water
4) if you're not using gloves, from here on keep you hands clean and non-greasy
5) make sure the fumes from the HCl solution doesn't cause any clips or what-have-you from corroding and dripping cr@p into the solution
6) 1M HCl is fine - but 5 to 10mA / cm2 is still way too high current density - try 1/100th of that slowly over a few days.
A good starting place is to directly connect the silver to the platinum electrode you are using as the negative (through an ammeter). Whatever current flows naturally - use around that order of magnitude. The current will drop with time when connected together.
Set a constant current power source (Ag to positive) at the required current setting and plot the voltage required to keep that current happening over time. it will gradually come to a plataeu. You can stop there but I would go for another overnight period.
Steep in distilled water overnight as suggested previously.
KEEP ADJUSTING THE pH TO KEEP IT STABLE. it will rise as the reaction takes place. 1M should be around pH = zero
- Perth, Western Australia
Q. Hi,
In reference to the above suggestion I have a query. When you maintain a constant current then the potential slowly increases, we have to take care that the potential does not increase that much that it dissociates water which results in a oxide layer deposition on silver wire?
- Enschede, Netherlands
March 2, 2012
A. Yawah,
that's the point of using acidified solution and not just some NaCl solution. The high level of acidity will prevent oxides from forming.
Matt
- Perth, Western Australia
May 2, 2012
Matt
Thank you very much for sharing this information and experience.
- Saudi Arabia
May 17, 2012
How to coat Ag/AgCl onto ABS for EKG electrodes?
Q. How to coat Ag/AgCl [silver/silver chloride] on ABS [acrylonitrile butadiene styrene] for EKG [electrocardiogram/ECG] electrodes? This is for developing ECG electrodes.
Hasmukh RamoliyaSurgimed - Vadodara, Gujarat, India
2005
Q. Hello
We are a producer of ECG electrodes.
We need Ag/AgCl plating on ABS.
Please advise what to do for that plating?
best regards,
pantamed - Iran
September 6, 2008
Q. I would like to know the process to plate Ag/AgCl on ABS plastic ECG Electrodes?
Nikhil Nagarindustrial user - India
September 17, 2009
by American Society for Electroplated Plastics
on AbeBooks
or eBay or
Amazon
(affil links)
A. I spent some time on Google and am beginning to get an understanding of your ECG electrode needs. It seems that silver must be electroplated onto the ABS, then the silver is anodized in a solution of KCl or similar salt to form an adherent AgCl coating on the silver. In use, a conductive gel is placed between the conductive probe and the patient's skin. I understand that the Ag/AgCl probes offer advantages over a plain metal button, but I don't know enough about ECGs to understand why :-(
Please see letter 31550, "How high quality plating on plastics is done" to understand the metallization and electroplating of the ABS, and see if it makes sense to you.
You might get better results if you write a paragraph or two explaining the principles you are thinking about and the issues you are trying to solve, because readers like myself may have a pretty good understanding of metal finishing, but often we don't understand very brief questions which require knowledge about a particular field or application :-)
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. I would like to know the process to plate Ag/AgCl on ABS plastic ECG Electrodes?
Ehsan Akbari- Iran
May 9, 2013
Hi Ehsan. As you read, I tried to answer that exact question. If my answer was not clear, please try to clarify exactly what info you seek. To simply cut & paste, and repeat letter-for-letter, a question that has just been answered is non-productive. I guess I shouldn't mention mention insulting :-)
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 2014
Ag/AgCl Electrode Problems
June 25, 2008Q. Initially we used a 2 mm pellet electrode made of Ag/AgCl as anodes and cathodes both to stimulate Brain. We used one anode and 4 cathodes. One anode in the center and 4 cathodes around it. With this configuration we sent dc current through anode. Approximately 1 mA current for about 10 minutes. But never this aAg/AgCl pellet electrode allowed us to send this much of current for 10 min.
As we started sending DC current through that electrode resistance of the electrode started increasing to very high values. Most of the times this shoot up of resistance returned back to normal value of resistance within 2-4 minutes after stopping the dc current.
Because of this problem we could not stimulate for more than 3-4 min, maximum 5 min. with 1 mA current. As increase of resistance decreases current. Commercially available stimulator are designed in way that they can send only up to 67 volts. So, if our scalp contact resistance is 8 k-ohm, that means with 1 mA, almost 8 volt is the voltage drop. But because of those electrodes resistance shoots up to very high values within very less time, that means if we keep current same so voltage start increasing. Voltage also shoots up because of resistance.Within 3-5 minutes resistance increases to such a high value that voltage reaches to threshold voltage of machine and then stimulation stops. We could never stimulate with 1 mA current for 10 minutes.
The wear and tear was visible as there colour also changed from grayish tone to dark black colour, only of that electrode that we used as compared to fresh ones.
So, we changed our pellet ( 2mm ) electrode with 8 mm disc electrode as anode. Which could easily bear this much of current with out any significant change in colour or its resistance even for more than 15 min with 2mA current.
1) We don't know what's going on in these Ag/AgCl electrodes, why small electrode could not bear this much of current while disc electrode could easily bear.
2) we cannot predict the life of disc electrode with different current input.
3) We cannot relate the size and shape of electrode with its capability to bear dc current.
Student - Bronx, New York
Need consultant/supplier to automate our Ag/AgCl plating
RFQ: We want to automate our coating lines and are looking for the services of an expert in the field. We process approx. 30-40 million Ag/AgCl sensors for use in ECG electrodes. Please feel free to contact us with your company name and/or credentials.
Salvatore E [last name deleted for privacy by Editor]Leading supplier of Ag/AgCl sensors for ECG electrodes - Fitchburg, Massachusetts
November 22, 2009
Ed. note: Sorry, this RFQ is old & outdated, so contact info is no longer available. However, if you feel that something technical should be said in reply, please post it; no public commercial suggestions please ( huh? why?)
Selective Plating of Ag/AgCl for Fast, Reel-to-Reel Wire Application
Q. Trying to develop new product in electrocardiology field, specifically disposable ECG electrodes. The ECG electrodes sense micro/millivolt pulses & feed them to a ECG signal storage unit for later analysis by cardiologist. I need to selectively plate silver, silver chloride over a flat wire. The wire has been through a die & has a copper strike over a steel wire. Nickel plating is done over the copper strike.
Need a high speed plating line. Material is put-up on reels and would necessitate a "reel-to-reel" high speed electroplating production line. Existing plating is done via electroless plating bath over treated plastics.
Application Engineering - Tampa, Florida, USA
February 10, 2015
Q. I would like to know the process to plate Ag/AgCl on ABS plastic ECG Electrodes?
Yasaman Eslami- Iran
April 30, 2018
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