Removing rust with electrolysis

SouthArk370Z

This might be useful if you have some rusty car parts you want to clean up.

A friend of mine has three old (late-1960s) Coleman lanterns that have been laying around in a shed for several decades. The valves and tubing are brass - not too hard to clean up. The tank ("fount" in Colemanese), cage around the globe, top hat, and handle are all steel - LOTS of rust after being neglected for so long.

We decided to try making one working lantern from all the parts. A quick look on The Intertubes led us to electrolysis. The electro-chemical reaction is rather complicated but the process is very simple. Many videos on Youtube.

WARNINGS:
* You'll be using electricity around an electrolyte (conductor) - there is a chance of shock. Since the charger shouldn't put out much more than 15 VDC, it won't be a big shock but it may startle you (similar to dipping your hands in salt water and touching both posts of a battery, you may not feel anything).
* This process gives off Hydrogen and Oxygen gasses. These are very explosive if they are allowed to build up. Only perform in a well-ventilated area and away from any ignition sources.
* Sodium Carbonate is a surfactant (soap) and will dry your skin out. Gloves are a good idea. Wash thoroughly if you get any on you. Don't eat it, breathe it, or get it in your eyes.
* The use of chrome/stainless steel/etc in this process can produce hexavalent chromium. Use only iron and/or steel.
* It's not a bad as it sounds. Sodium Carbonate is safe when handled carefully. The explosive gasses dissipate easily with a little wind. The shock risk is low. Don't put anything with chrome in it into the electrolyte.

Supplies:
* Container large enough to cover your part in electrolyte.
* Steel/iron anodes - we are using a piece of steel rebar and parts from a steel wire shelf.
* Sodium Carbonate (AKA washing soda) (not Sodium Bicarbonate, AKA baking soda) - you should be able to find at most grocery stores. We had an old box of Arm & Hammer brand in the back of a closet. You don't need much; about 1 tablespoon per gallon of water.
* Water to fill container.
* A bar long enough to span your container and suspend part in electrolyte. Non-conductive is best.
* Battery charger. If you can find a "dumb" charger, it will work better. The "smart" charger we are using requires us to put a car battery in the circuit. Our setup is pulling up to 15A but most of that is going into the worn-out battery we have; process takes less than 5A.
* Small-gauge wires to connect charger/battery to part and anode(s). 18-24 ga works well. Jumpers with alligator clips would be handy.


Set the container in a well-ventilated area, away from ignition sources, add approx 1 tablespoon of soda per gallon of water, then fill with enough water to cover your part.

Attach wires to anode(s) and part. Place anode(s) at edge of container and hang part from support rod so that it is NOT touching the anode(s). I'm using some steel wire to hang the part from and negative power wire to that). Copper turns into an ugly, green crud when you get electrolyte on it.

Connect wiring to charger - negative to your part and positive to the anode(s) - and turn charger on. If you get the polarity wrong, you will make MORE rust on your part.


Almost immediately, you will see tiny bubbles coming from your part and the anode. This is the Hydrogen and Oxygen I warned you about.

How long you have to leave the process running varies from a few hours to a few days, depending on size of part, how bad the rust is, and how much current you have flowing.

When the steel turns black, it has been converted to magnetite (another form of iron oxide that isn't as nasty as rust). This can be sanded/painted or allow the process to run longer and it will turn into silvery, unoxidized iron.
Since the rust is being converted back to iron, pitting will be less than with sandblasting or acid etching.


At the end of the process, you will need to properly dispose of the electrolyte and the sludge at the bottom of your container. The electrolyte is just washing soap and the sludge is rust - neither is particularly nasty but the rust will stain stuff. I will be decanting the electrolyte and diluting it before sending down the drain. I'll dry and save the rust sludge for future experiments.

Enjoy

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