Wooden frame that will become the "tank"
Written: November 20, 2021
The advantage of removing rust by electrolysis is that only rust gets removed. You aren't inadvertantly scraping away metal with abrasives. Not only that, there just might be less elbow grease involved. We shall see. For me this isn't all about saving work, but about giving this electrolysis thing a try.
Then I used a carpenters level to locate a level spot in my yard. Getting it level ensures that you won't have solution spilling out of one corner and that a minimum amount of solution will be needed to evenly cover what goes in the "tank".
I have a roll of plastic sitting around that is labeled 3.5 mil plastic sheeting, 10 feet by 25 feet. I cut off 32 inches and the resulting 32 inch by 10 foot piece works perfectly. I use my staple gun to put 4 or 5 staples on each side and in go the parts.
The way this works is that you fill the tank with an ionic solution. I used 7 gallons of water along with 7 tablespoons of washing soda (sodium carbonate). People say plain old baking soda (sodium bicarbonate) works just fine, so don't make yourself crazy hunting around for washing soda.
What I did was to fill the tank with 7 gallons of water, then add spoonfuls of washing soda. If I had it to do again, I would make 3 batches of about 2.5 gallon size in my 5 gallon bucket, mix them thoroughly, then dump them in. But suit yourself, it all gets mixed up eventually. Just avoid poking any holes in the plastic.
Then you need a DC power supply. Many people use a battery charger. I have two and neither works. They are too smart and recognize that whatever it is you have them connected to isn't acting like a battery and refuse to do what they should. If you have an old school battery charger that doesn't outsmart you, you will be fine. I have all kinds of electronics available and did my initial setup with a 24 volt 10 amp unregulated supply I had available. Later I switched to a 33 volt, 33 amp lab supply that worked wonderfully; I could turn the knob to 15 volts and watch the current on a display.
Once you have your power supply, you connect the negative side to the part you want to clean and the positive side to some scrap iron you don't care about. I had a couple pieces of rebar laying around, so I used those. I cleaned up the ends with a wire brush (probably not required) then wrapped bailing wire around them. I also used bailing wire to make the connection to my saw blade. The idea is that nothing other than iron goes into the bath.
You will see in the photo above, that bailing wire is stiff enough to reliably make a bridge up out of the solution and over the saw blade. I connected the bailing wire from each piece of rebar together and connected them to the positive side of my power supply by just twisting the wires around each other.
I made connections in the most quick and dirty way imaginable. I just twisted wires together, wrapped wire around dirty rusty metal. I was shocked that it all worked just fine. The setup was immediately pulling 8 amps as soon as I fired it up. So don't go nuts fussing over the connections, this hookup is going to be in service for only a day or so.
You make all the connections and turn on the juice. In my initial setup, I included an 0.2 ohm resistor in series with one side of the system to allow me to measure current. Measuring the voltage across this resistor tells me the current by a simple calculation involving Ohms law, i.e current = voltage / resistance. I measured 1.6 volts immediately (8 amps) which surprised (and pleased) me.
Away it goes. How long should it go for? I let mine run for 5 hours with 8 amps going through it. As it runs, there is a buildup of brown colored foam, especially above the rebar. There are weird smells and it starts to look like (but isn't) an environmental disaster. At the end there are less bubbles, but current seems to be staying at 8 amps and if anything slowly creeping up.
What current? The fancy charger I used later in the game allows me to set a current limit, but most folks won't have this ability and it doesn't matter. Your setup is going to want to pull a certain amount of current. This is in large part determined by the surface area of the object you are cleaning (and probably also the sacrifical negative electrodes). I also wonder if the amount of washing soda in the water relates to the current; perhaps putting in less washing soda could be used to control how much current is drawn.
A charger for a car battery will either freak out and stop charging, or just limit the current if your setup pulls a lot. Hopefully the latter.
Your object to be cleaned is negative, so it will attract positive ions in the solution, namely sodium ions. When these get to the negative electrode, they will become sodium atoms, but these are unstable in the presence of water, so we immediately get hydrogen gas and sodium is back in solution again (along with the production of hydroxyl).
What goes on at the positive electrode? Some people call this a sacrificial electrode, implying that iron is going into solution and then getting redeposited on the object to be cleaned. I don't buy it. One reason is that people talk about using graphite electrodes, which clearly are not going to react or dissolve. One thing is sure from inspecting the positive electrode, something is going on. They get nasty looking and I see what look like crystals of something growing on mine. Some folks say that the bubbles that come up from the sacrificial electrode are oxygen, and perhaps they are.
You will read cautionary advice about not using stainless steel for the sacrificial electrode. I wasn't tempted to do so, but the reason is that chromium will dissolve in the solution and yields nasty toxic compounds.
You could probably use salt in lieu of sodium carbonate, but you would be producing chlorine gas at the positive electrode. I would not consider this a "good thing", but if you were desperate and doing this out of doors, well just stay upwind and cross your fingers.
You will also read a lot about ferric (brown) iron oxides (i.e. rust) being converted to black (ferrous) iron oxides on the object to be cleaned. Maybe so, but it looks to me like a lot of the rust is just being loosened. My saw blade is covered by a layer of fine brown sediment once the process finishes.
Some people claim that what is really going on is that hydrogen gas produced on the object to be cleaned is just physically dislodging rust and no reduction chemistry at all is going on there involving iron. I just can't say one way or the other myself.
Tom's Computer Info / tom@mmto.org