Most of us have at one time or another, flipped the gas cap of a bike you either own or plan to own and seen the dreaded rust blooms everywhere. Because I appear to have plenty of time on my hands I decided to have a go at using electrolysis. My friend down the street has a number of tanks with rust so we decided to try one of his.
The theory is fairly simple, you direct current from one spot to another through a liquid and get the current to carry the rust molecules with it, transferring them from the tank surface to your anode. This is almost the same principle as plating where you employ a cathode of the material you wish to transfer and an anode, the item you wish to transfer the molecules to except in this case the inside surface of the tank is considered to be the cathode.
You need a medium to transfer the rust and a solution of carbonate of soda in water is sufficient. (Not BI-carbonate of soda or baking soda. You need a washing soda. You can create carbonate of soda by heating bi-carb in your oven at 350' for about 20 minutes.) About half a cup for 5 gallons is right. We found the carbonate of soda at the local Home Hardware.
Next you need a a piece of iron to act as the anode and we used a 6" piece of rebar. You'll see the plastic cap on the top and a bit of plastic on the end of the rebar. This was to prevent the rebar from grounding out anywhere on the tank surface so the current would only flow to the rebar through the liquid.
The voltage and amperage to use can be decided leaving a lot of wiggle room in case your power supply isn't a heavy duty one. Along as the current is flowing fairly evenly at around 2 amps and 12 volts you will get the desired result. You probably want to monitor this activity during the day in case the solution bubbles over or the power supply gets too hot.
Fill the tank right to the brim with your soda solution, set the anode in so there's no metal to metal contact, fix the positive to the anode and the negative to something like the fuel tap or some other well grounded part and you're ready to go!
We had to use a shorter anode because of the hump in the tank so we had to clean the deposits off the anode a couple of times.
As you can see from the photos, the process is fairly straight forward and leaves only a few specks of rust after the second treatment. We then dried the tank out and splashed some kerosene around to coat the bare metal. I have one more photo of the finished process coming and will upload it later.
This sort of process works especially well in tanks that have lots of small crevasses where shaking a bunch of nuts around wouldn't reach all the spots.
There's a few YouTube demo's available too.
Finally - it's probably a good idea to do a careful examination of the seams of your tank for any bubbling to ensure all that rust hasn't actually eaten through the metal.
