Anyone made a sliver/silver chloride reference electrode?

[GHA]

There is a rather expensive one onboard my steel boat already to check how the zincs are doing, but would be nice to make a cheap one which could live over the side when not under way to keep an eye on things. Raspberry pi already exists to measure the voltage and record it.

Anyone made one?

Some stuff on the web but seems more lab based.

Ta

 

[Roberto]

I used one of those medical electrodes, they come in dozens for a nominal price. Usually ok for one set of measurements, they then have to be replaced with new ones.
Mine is a plastic boat, I would buy a proper one for a metal boat needing almost constant checking.
Somewhere I have the address of a cheapish commercial one, I ll try and find


In pre-photobucket times I made a post here with the medical electrodes, I understand of not much help now
http://sybrancaleone.blogspot.fr/2011/10/controllore-protezione-galvanica-fai-da.html


Add: Ag/AgCl medical electrodes are those sticky patches (often 3M) with a tiny metal cell in the middle they work very well but do not last very long

 

[GHA]

Thanks Roberto, I have a calibrated one already but don't like the idea of leaving it immersed for long periods of time so thought I'd look into making something cheaper. Some bits did come up on google just using a piece of silver wire or creating a silver chloride layer by immersing silver wire in bleach.

 

[Roberto]

Thanks Roberto, I have a calibrated one already but don't like the idea of leaving it immersed for long periods of time so thought I'd look into making something cheaper. Some bits did come up on google just using a piece of silver wire or creating a silver chloride layer by immersing silver wire in bleach.

Well if you need something to be used occasionnally, imho the medical ones are perfect.
Just connect their "push button" side to a piece of wire, then insulate the connection with some putty, silicone of whatever, bring the wire onboard to one side of your multimeter. Peel off the opposite adhesive side and stick it to a piece of plastic with a hole, so that water can come in contact with the metal piece, add some weight to:let it go underwater for measurements.
From what I have heard from people having aluminium boats (and care about this type of measures, which is not frequent), even semi professional electrodes with thick surfaces do not last long if used continuously, maybe the "use once and throw away" is not a bad middle solution ?
I am sure you have anything you need, anyway a couple of pictures here (where I copied mine) might give some suggestions:
http://www.plaisance-pratique.com/mesures-de-controle-en-protection

 

[GHA]

Thanks again, useful link.

I found some more on a allaboutcircuits thread -
https://forum.allaboutcircuits.com/threads/help-needed-bond-ckt.84645/page-2

Looks like he had success using a sliver earring as an electrode.

 

[VicS]

How to make a silver / silver chloride electrode

From "Analysis with Ion Selective Electrodes" by P.L. Bailey. ( ISBN 0 88501 223 4)

Clean a pure silver wire in strong ammonia solution; rinse; dip in 50% nitric acid until the silver is an even white colour ( usually about one minute). Rinse with distilled water but do not dry.

Cathodize the silver wire against a silver anode at a current density of 0.5 - 10 mA cm ^-2 ( about 5mA cm ^-2 is most suitable) in 0.1 M hydrochloric acid ( analytical reagent grade) for 30s. Allow bubbles to disperse from the wire.

Anodize the wire for 10- 15 min at the same current density. Rinse.

I knew I had the instructions somewhere because I made one years ago. Just taken a while to find them.

Can't find the electrode though nor the surplus silver wire!

 

[GHA]

How to make a silver / silver chloride electrode

From "Analysis with Ion Selective Electrodes" by P.L. Bailey. ( ISBN 0 88501 223 4)



I knew I had the instructions somewhere because I made one years ago. Just taken a while to find them.

Can't find the electrode though nor the surplus silver wire!

Thanks Vic!! If i read that many times I might understand what's going on with the aid of google
Most should be achievable onboard with a current limited buck converter and with a visit to a Portuguese supermarket barring nitric acid.

Looking at the galvanic scale - silver on its own is only about 0.1v above Ag/AgCl and there are examples on google of peope having success, i wonder if silver would work on its own with an offset programmed in? Precise measurements aren't really that important, with a proper Ag/AgCl reference cell onboard it should be possible to calibrate then watch for any drift in the DIY version.

Maybe.. But any data is good if it gives you a heads up that something is different.

 

[GHA]

Still not sourced any silver to play with but came across this circuit, which seems like good idea, basically a "volume control" for a zinc. This was for a boat moored in a tidal river to keep the voltage stable as the salinity changed. Reading a bit more it was actually an old silver coin he was using as a reference electrode. Seems to work OK with an offset.

 

[Hydrozoan]

... "Analysis with Ion Selective Electrodes" by P.L. Bailey. ...

That brought back memories – though not of making them: I commonly used the Orion type with sleeve junctions rather than frits (for high accuracy laboratory pH and fluoride ion determinations). I don’t know anything about Ag/AgCl electrodes in corrosion monitoring, but presume that those without a KCl electrolyte and liquid junction are restricted to conditions of unvarying salinity.

Closely matched pairs of very high stability Ag/AgCl/KCl electrodes were used to estimate marine current flows from the EMF generated by the water’s passing through the earth’s magnetic field – particularly by W S von Arx of Woods Hole in the 1950s who towed his ‘GeoElectric Kinetograph (GEK)’ from this vessel: http://www.whoi.edu/page.do?pid=83503&tid=4142&cid=1551