Thread: Electrolysis using an old computer power supply

Originally Posted by BobL

The empty carbon arc rod packet I saw at work says 80-90% carbon and 10-20% copper.

I'm not sure it matters in most cases if the iron gets some copper deposited on it anyway, it will just protect the iron.

If it is, just soaking them in aqua-regia for a day will dissolve out the copper, at least far enough into the rod to stop it fouling the electrolysis.

hi do you know what oxygen press you use on a carbon arc cutter

Originally Posted by azzrock

hi do you know what oxygen press you use on a carbon arc cutter

Sorry can't help there - I've never done it myself.

I saw this thread earlier today, and it caught my eye as I'd never come across this process before.
I dabbled with electroplating and anodizing years ago - which use a very similar process, but hadn't heard of it for rust removal.

So, I did a quick bit of background reading then rummaged through the laundry cupboard to try and find a suitable alkaline electrolyte that didn't contain NaCl.
It turns out that Sellys liquid sugar soap is perfect for the job (but probably the most expensive way to do it).

So off to the shed to grab a plastic mop bucket, a bench power supply and a chunk of sacrificial steel... and a suitably rusty test piece.




About 4 hours in the tub, then 10 minutes cleaning up resulted in this:



There's no doubt that this is a gentle process, after it was cleaned up you can see every little score and burr on the arbor, I certainly hadn't noticed them under all that rust before...



I went out and bought a bag of washing soda this afternoon, because I think I'll be using this process a fair bit in the future.

Originally Posted by festy_

So, I did a quick bit of background reading then rummaged through the laundry cupboard to try and find a suitable alkaline electrolyte that didn't contain NaCl.
It turns out that Sellys liquid sugar soap is perfect for the job (but probably the most expensive way to do it).

Sugar soap contains ~60% Sodium Phosphate, 30% Sodium Carbonate and 10% sodium meta silicate. I don't mind sticking my hands in baths salts (sodium carbonate) but sugar soap is a bit more aggressive although there's not much of an issue if its diluted down enough.

Baths salts from coles is the cheapest I could find Sodium Carbonate for $4/kg - only about 5 g/l is required.

That's the powdered sugar soap.

The liquid version is much better, according to the MSDS it contains water, sodium carbonate and sodium tripolyphosphate - both of which are well suited to the process.
As I said, a rather expensive way to get sodium carbonate - but it was just a test run. The pure sodium carbonate was only a couple of dollars for 500g so I'll stick with that from now on.
I've got an old spanner that I found rusting in a paddock in the bucket at the moment with the lectric soda, hopefully it turns out as well as the first piece did.

Came up great Bob. I'm going to have to remember this one.

Stuart

Originally Posted by Stustoys

Came up great Bob. I'm going to have to remember this one.

Stuart

Given how pitted and rusted it was I'm happy enough with the way it turned out - it's being painted at the moment.

The rusty railway plate is proving a bit tricky - it's not just rust, there's sand and a sort of tarry crusty layer that's taking a lot longer than usual to make any head way with. I even gave the plate a couple of hours in raw spirit vinegar to see if the layer was calcium carbonate but there was no fizzing so my guess is it's just hard compacted rusty tarry sand. I took it out about an hour ago and scrubbed the tarry stuff with a stiff wire brush and that scraped some of it off.

Here's the railway line plate after 48 hours in the electrolysis unit.

Alongside is another similarly rusted plate that is now in the bath.

While it looks pretty good, a close up reveals that even 48 hours would not get all the scale off even with a bit of a wire brushing to help it along.

That works good. I have a few things around here that could do with it.

Dave

wow Bob, would take ages with a wire brush to even get close to that good. I think only thing that would be better would be sandblaster and you have to be there working for that to do anything
Stuart

Originally Posted by Stustoys

wow Bob, would take ages with a wire brush to even get close to that good. I think only thing that would be better would be sandblaster and you have to be there working for that to do anything
Stuart

Although it wouldn't matter in the case of the railway plate, a sandblaster can also be pretty abrasive.

It's not all beer and skittles. I had to clean the anodes probably a dozen times over the 48 hour period - usually I just sweep them side to side but several times I had to wipe them down with a rag. I wore disposable gloves while doing this otherwise my hands went black and were hard to get clean. There is certainly a lot less sweat involved.

Once I have finished the second plate I'll pack things in for while - SWMBO wants the back veranda back

Good point about the sandblasting.
What happens when the anodes get dirty? does the current just drop off?

I stumbled on this post, giving a bit more of an insight into using old PC power supplies.

TheBackShed.com - DIY CNC

Ken

Originally Posted by Bushmiller

BobL

I have always used stainless steel for the sacrificial annode. It lasts far longer than mild steel. I make a point of picking up scap SS for just that purpose.
Regards
Paul

G'day Bushmiller and all,
I am no chemist at all, but there is a body of opinion who argue that using stainless steel for the anode is likely to cause the formation of highly toxic hexavalent chromium compounds, because the chromium content of stainless steel may be leached out, or more correctly may react with the other compounds present in the solution. I might add that I have used a large ss bin to act as both the containing vessel, and the anode when de-rusting electrolytically. As you have said Bushmiller, there is no problem with it corroding, and no need to stop to clean the anode as you must do when using iron or steel. I have no idea whether any toxic compounds were formed at all, or indeed if it is likely that they could form in the likely conditions encountered in the amateurs workshop. If it is possible for hexavalent chrome compounds to be formed, it might still be something we could control by the appropriate choice of voltage, current density or even materials used for the electrolyte. If we have any budding industrial chemists or their ilk on this forum with appropriate knowledge of this branch of chemistry, perhaps they could inform us of the likely situation regarding the formation of these compounds, or even tests we could perform to detect the formation of them.
In the meantime I am trying to locate some graphite sheet to use for the anode, as there would be no chance of it plating out as other metalic materials will do, and as far as I know, no chance of forming dangerous compounds either. If anyone has a local source for graphite sheet or bar / rod at reasonable prices, I would be very grateful for the heads up. I have found a seller on U.S. eBay, and his prices seem quite reasonable, but the freight would not be cheap, so a local seller, especially if he deals in scrap or off-cut material could be a deal maker.
I used a battery charger (Arlec Charger4) as my power source but I like the idea of using scrapped PC power supplies because of their much higher currents enabling a faster reaction most likely Thanks to all contributors for your input, Cheers all,
Rob