Thread: Electrolysis solution longevity

Hey, thanks guys. I failed chemistry in a big way at school (spent too much time piping water into the gas lines ) so I'm really enjoying this read and lessons.
I was always under the assumption that SS was they way to go for the anodes...that how it's always been in my readings over the years...so this new info is great to have and quite interesting, particularly in regards to toxic contamination of the solution. The hydrogen bubbles were always just a bit of fun to know about, but I do try to keep the area ventilated just in case of "kabo0m"

Originally Posted by RedShirtGuy

I was always under the assumption that SS was they way to go for the anodes...that how it's always been in my readings over the years...so this new info is great to have and quite interesting, particularly in regards to toxic contamination of the solution.

I wouldn't describe it as contamination -- as far as I know, the presence of Chromium salts has no impact on the effectiveness of the solution.

The hydrogen bubbles were always just a bit of fun to know about, but I do try to keep the area ventilated just in case of "kabo0m"

the ventilation suggested by Bob is is less about a possible KABOOM and more about dispersing the aerosols which potentially are a source of ingested chromium (VI)

Originally Posted by ian

I wouldn't describe it as contamination -- as far as I know, the presence of Chromium salts has no impact on the effectiveness of the solution.

the ventilation suggested by Bob is is less about a possible KABOOM and more about dispersing the aerosols which potentially are a source of ingested chromium (VI)

Actually I was just as serious about a KABOOM , there are several vids on other forums using typical battery charger setups that have resulted in explosions.

Typically what happens is containers are used that are too tall, sometimes covered, and the higher voltages produced too much current hence too much hydrogen.

Then instead of switching the PS off, wires are just disconnected from the objects being electrolysed and any resulting small spark ignites the gasses.

The worst one was a guy using a 200L plastic drum about half full of electrolyte. The explosion set his eyebrows and hair on fire but fortunately it was put out by the 50 odd litres of filthy brown orange electrolyte ejected out of the drum. He also soiled his pants in another way during the process.

I'd love to know more about how the ss is dissolved. I've always thought of electrolytic cleaning as a sort of 'reverse plating' where the oxide on the anode is removed as though it was the plating metal and moved to the cathode where it doesn't actually plate because it is not compatible (so to speak).

So in my mind the ss should be completely inert.

Apparently I am wrong!


Russ

Originally Posted by russ57

I'd love to know more about how the ss is dissolved. I've always thought of electrolytic cleaning as a sort of 'reverse plating' where the oxide on the anode is removed as though it was the plating metal and moved to the cathode where it doesn't actually plate because it is not compatible (so to speak).

So in my mind the ss should be completely inert.

Apparently I am wrong!

Russ

Actually you make a good point, but it sounds like you are referring to using anodic cleaning.
Most DIY think of electrolysis as a way to convert rust to metal process whereas practically none of the rust is plated back onto the workpiece surface - instead the rust is actually removed or cleaned.

There are two forms of electrolytic cleaning: from https://www.corrosionpedia.com/defin...lytic-cleaning

• Anodic electrocleaning - The workpiece is made the anode in the system. This is performed in a basic solution to facilitate the oxidation reaction 4(OH)- = 2H2O + O2(g) + 4e-. Oxygen gas bubbles are generated directly at the workpiece, beneath the contaminant, which helps lift and remove the rust, deposits and light oils.
• Cathodic electrocleaning - The workpiece is made the cathode and a reduction reaction occurs at the surface. In this case, the pH of the system needs to be acidic to provide sufficient hydrogen ions to sustain the reaction 4H+ + 4e- = 2H2(g). In the same manner, it lifts deposits like rust or oxide from the metal surface.

Most DIYers use cathodic cleaning with basic solutions because then you cannot damage the surface of the object being derusted even if you leave the work piece in there for a long period. The belief is longer must be better which is not always the case. If an acid is used and forgotten about the workpiece will dissolve over time.

If anodic cleaning is used the electrolyte must be kept basic and be done for a very short time period otherwise the continual generation of oxygen at the surface will also dissolve your work piece.

The most efficient electrolytic cleaning uses repeated pulses of cathodic and anodic cleaning.
However, the time periods involved are in the seconds to minutes range.
Apparent this also helps keep the electrodes clean so no wiping is need

I have tried anodic cleaning but wanted a set and forget method so I switched to cathodic cleaning with an carbon anode.
I should go back and give the anodic method a try now that I have some more controllable PS.
In recent times I have been using oxalic acid as a rust removal process. Although it is relatively slow its a dunk and forget about process and does not dissolve any of the steel.

What time periods are you using for your anodic cleaning Russ?

I just use a few teaspoons of caustic soda in a few gallons of water but I was using 36v.
Cleaning time usually a few hours.

A little bubbling but not a lot so I assume a low current. (the ps is regulated to 4a so less than that but I didn't ever measure it.)

A large (say 200x350) as plate as electrode


Russ

Originally Posted by russ57

I just use a few teaspoons of caustic soda in a few gallons of water but I was using 36v.
Cleaning time usually a few hours.

A little bubbling but not a lot so I assume a low current. (the ps is regulated to 4a so less than that but I didn't ever measure it.)

A large (say 200x350) as plate as electrode

Thanks Russ,

Back of the envelope calculation , 3 tsp in coupla gallons is about 15g in 10L, 1.5g/L which will have a pH between 12 and 13.
I'm surprised you don't see any pitting over about two hours.

I use Sodium carbonate (foot bath salts) about 40g/L which has a pH of about 12.
With < 6V with resulting currents are between 3 and 4A and cleaning generally takes so it takes between 4 and 6 hours
However, I'm using cathode cleaning which is know to be slower - I will give anodic cleaning a go next time.

Possibly more like 40l

I'm surprised that the pH would be that high but I've not really considered it.
I havent observed pitting but if I did I would put it down to the result of the rust not the cleaning.




Russ

Originally Posted by russ57

Possibly more like 40l

OK so ~8 gallons, that would make it about 0.4 g/L so pH around about 12.

I'm surprised that the pH would be that high but I've not really considered it.
I havent observed pitting but if I did I would put it down to the result of the rust not the cleaning.

Fair enough.

Some great advice on this thread about removing rust.

I, however, have a different problem...

I need a load of rusty nails.
If I put a load of steel nails in some sort of steel mesh bag, on the positive terminal, and dipped it into the bucket with an old rusty horseshoe, on the negative terminal, would it make my new nails look old?

Sounds a bit complicated I know, but a bit of advice would be appreciated. Thanks

Originally Posted by B & HA

Some great advice on this thread about removing rust.

I, however, have a different problem...

I need a load of rusty nails.
If I put a load of steel nails in some sort of steel mesh bag, on the positive terminal, and dipped it into the bucket with an old rusty horseshoe, on the negative terminal, would it make my new nails look old?

Sounds a bit complicated I know, but a bit of advice would be appreciated. Thanks

That will pull metallic iron off the nails and leave behind an orange sludgy mess which will wash off leaving a black pitted surface (is this what you are after?) which will then develop a patina of thin rust if left exposed to air. If you want them to finish up with reasonably thick flakey layers of rust on then you will then have to leave them exposed to air for some time..

Either way any oil/grease dirt etc should be removed by using suitable solvents etc.

If you want the nails to have a thicker layer of rust you might get a quicker result by dunking them in hydrochloric acid for a few minutes and then laying them out so they are fully exposed to air. To speed things up, if they dry out spray them with dilute HCl every day they should work up layers of rust.

The RHS cog was sprayed with vinegar and shows what happens. The rust is friable (physically not robust) - if you want robust layers of rust you have to let it develop by itself in moist warm air.

2ndpassa.jpg.