A "better" electrolysis driven rust remover

[PyroNeuby]

So I'm new but know there's been plenty said already on using electrolysis for rust removal. Washing Soda (Sodium Carbonate), some scrap steel and a trickle charger.

Immediately you start to see the blue-green/gray scale build on the anode (scrap steel) which later turns the familar rust red. Stop the reaction, scrape the anode off and continue only to stop and scrape some more.

The problem is in the chemistry. The initial blue-green/gray stuff is iron (ii) carbonate and perhaps a little iron (ii) hydroxide. Both of these compounds are not soluble in water whatsoever. The anode gets coated in the stuff slowing the reaction down as the iron (ii) coating becomes red iron (iii).

Metallic iron can give up 2 electrons initially Fe -> Fe2+ + 2e-. The Fe2+ can only give up one electron Fe2+ -> Fe3+ + e-. You need the electrons to remove the rust on the piece you are restoring, so once your anode gets coated, the reaction speed slows by half or more.

The other problem is on the cathode end (your piece being restored). The black magnetite coating that develops; it's porous, holds moisture, and can be troublesome to remove.

The solution is in mixing a better electrolyte. Both acetate and citrate salts readily solublize iron and citrates can coat and hold magnetite in a colloidal suspension. And both are readily available and inexpensive.

Vinegar is acetic acid and many radiator flushes contain citrates (Prestone Flush is Sodium citrate and water, nothing else). So let's react the vinegar with some baking soda (or washing soda, doesn't matter in this case), and then add the citrate based radiator flush. Dilute these with water, and you have an electrolyte solution that allows for a far more efficient process.

I'll post all the details soon, but so far all the small pieces (bib hinge, door hinges, spare tire latch) have only taken an approximate 2 hrs with absolutely no maintenance and the black magnetite coating is much easier to remove.

 

[Cruiserdrew]

Good luck but doubt it will work.

I think the bonded magnetite on the surface is OK as paint sticks to it just fine, and the stuff that isn't bonded just wipes right off.

I have heard of using Carbon (graphite) electrodes that don't corrode.

 

[PyroNeuby]

So far it's definately working. I went to college for chemistry (never finished sadly) so it's always fun to combine science geek in me with the cruiser nut.

5 Gallon formula:

First mix:
71 fl oz. of distilled vinegar
12 Tbsp of baking soda

mix until fizzing stops and all baking soda is dissolved

Then add:
22 fl oz of Prestone Radiator Flush/Cleaner

Fill remaining with water up to 5 gallon mark.

You wil notice the solution will turn a very dark rust red (ferric acetate forming) becoming eventually almost black (from the citrate chelated magnetite). The anodes stay clean because the iron stays soluble, and the reaction only takes a few hours.

You should be able to use and resuse the solution indefinately with some basic filtering. Should only need to add more of the radiator flush as the colloidal magnetite citrate will be filtered out.

I want to go large scale soon with it (front bib and grill or a perhaps fender (FJ40)). The ultimate goal is to successfully electrogalvanize most of the more rust prone parts of my '76 FJ40. To do that I needed a cleaner method. I've also done some research on the carbon electrodes, but they can be costly. Best part about this is I can dilute the solution once I'm finished and spray it on the lawn for a nice iron boost and happy green grass in the summer.

I'm currently giving the latch spare tire swing a bath using an old exhaust clamp for the anode. Here's the setup.

 

[Cruiserdrew]

The question is though, have you prevented the scale from insulating the anode?

The real advantage of the high pH solution is the solution prevents the cathode from itself corroding. That's why a solution of sodium hydroxide works so well as the electrolyte. It's just dangerous and hard to handle. The sodium carbonate is much safer to handle and isn't quite as effective.

By adding acids to your solution, you are making the solution itself corrosive which will tend to work against you. Plus it will make the surface more reactive even after you paint it.

I'm going to look into Carbon electrodes. I think that would work, and I'm wiling to do the experiment.

 

[PyroNeuby]

Carbon electrodes will definately work, but they will eventually corrode, as it too is oxidized (losing electrons), and need to be replaced as well. You can find some on Amazon. I also found a guy online doing model A Ford parts with carbon electrodes, he had a link posted to his supplier, don't remember the site though.

Scrap steel is plentiful and going larger scale would get expensive fast with carbon electrodes.

In my method the anodes don't become insulated because the sodium acetate/citrate mixture displaces the iron scale as it develops. Electrolysis in water will yield OH- (hydroxide-strong base) ions which will react with the anode producing the iron (ii) hydroxide scale. This is displaced by the presence of the acetate ion, iron acetate is soluble in both oxidation states.

It too is a high pH solution, you are reacting the vinegar with the baking soda which nets a sodium acetate (weak base) solution, then adding sodium citrate (another weak base). So there's no danger in acid damage to your cathode piece.