RUST REMOVAL BY ELECTROLYSIS
20 January 2005:
There are a number of sites on the Web that explain using electrolysys to remove rust. I'll just show some of my limited experiences with it.
Briefly, electrolysis is an electrochemical process that defines how batteries, electroplating, etc. work. You use Direct Current to force molecules of one conductor to move through a liquid that conducts electricity (called an electrolyte) to another conductor. In charging of a battery, the movement is accompanied by a chemical change in the plates that in some cases stores energy that can be recovered by reversing the charging process. In other batteries, the chemical change is not reversible and, once the chemicals are "used up", the battery can no longer produce current.
Electrolytes can be composed of numerous mostly water based compounds. A car battery uses a dilute solution of Sulfuric Acid as the electrolyte. An Edison or "Nickel-Iron" battery uses a saturated solution of Sodium Hydroxide as the electrolyte.
In the rust removal process, a mild caustic is used for the electrolyte. The rust from the cathode is moved by electrolytic action through the electrolyte to the positive terminal.
I've never been able to get ahold of the recommended chemical to use as an electrolyte. The recommended chemical is safe and is supposed to work well. The chemical is Sodium Carbonate, otherwise known as "washing soda". It is a common ingredient in powdered dishwashing detergents and other household cleaners. Sodium Carbonate is as safe to use as any household detergent. The cautions on it's use are the same as those on the box it comes in.
In lieu of that, I've used Sodium Bicarbonate, which is commonly available as Arm & Hammer (and other brands) "baking soda". This chemical is safe to use, but I've been told that it works more slowly than Sodium Carbonate.
I've also used products like "409" and the like. They don't conduct electricity as well as the above two chemicals but work pretty well. If you want to live dangerously, dissolve a small amount of Sodium Hydroxide or "Lye" in some water and add a few drops to the brew. This makes the solution conduct electricity much better.
CAUTION, CAUTION, CAUTION!:
- In this process, you're working with potentially dangerous chemical reactions. Among them are some that can cause serious injury. Do NOT experiment with unknown chemicals for the electrolyte!
- DO NOT USE SALT WATER as the electrolyte! Poisinous Chlorine gas is produced in quantities large enough to irritate your eyes and lungs.
- Electrolysis can generate a very flammable mixture of Hydrogen and Oxygen gas in closed places. Ventilate the area well!
- Be sure to use only carbon steel, cast iron or carbon for the anode. If, for instance, you use stainless steel as the anode, poison gas can be liberated and the electrolyte will become a poison that could kill you!
A couple of days ago, I needed to de-rust a piece of railroad rail I'd been picking at off and on for a while. I'm going to use it as an anvil. I couldn't find any detergents that I thought would work and didn't have any baking soda so I started looking at labels in my wife's cupboard. I almost passed-up a product I'm sure you've seen commercials for on TeeVee. The stuff's called "Oxi Clean" and is supposed to be able to remove just about any stain you can throw at it. Looking at the label, I saw that it contains Sodium Percarbonate and Sodium Carbonate.
I got the plastic bucket set-up and filled it with about 4 gallons of water. I put-in the rail and connected it to the negative terminal of my home-made power supply. I squashed a 4-lb coffee can and hooked it up to the positive terminal and dunked it into the pail using a piece of PVC pipe to keep the two electrodes separated.
At first, when I turned on the power, I could register about a half Amp of current at a little over 30 Volts. I added a scoop (it comes with the product) of Oxi Clean and stirred. The current went to around 7 Amps. I added another scoop and stirred and the current went to about 14 Amps. The third scoop only raised the currrent to about 19 Amps, so that's where I left it. I figure that if I added much more, I'd just be wasting the chemical so it looks like about a scoop to a gallon of water does it.
Boy, did it cook! After about an hour, the current had gone down to about 16 Amps because of the coffee can collecting crud and the mixture in the bucket had an ugly froth on it. At that current, the whole thing was getting a bit warm so I turned the voltage down 'til it was drawing around 10 Amps and figured to leave it to cook overnight.
When I went back out the next morning, the current was zero. The anode lead, which was just a strip of the coffee can that I cut to lead out of the bucket, had corroded in two, cutting the circuit.
This morning, I looked in the junk pile and found a flywheel off of a small Briggs engine that had been underwater for long enough to ruin it. I punched out the pins that held the magnet and diecast magnet housing, drilled one of the holes for a 5/16" bolt and bolted a piece of 1/4" diameter copper wire to it. I dipped it into the brew, cranked up the power supply and away it went again.
Here's a photo of the anode - a junk B&S flywheel. The copper lead-in wire may have to be replaced with some steel strap due to corrosion. A few hours in the tank working should tell the tale.
Here's the setup in my decidedly cluttered garage/shop. I just couldn't resist using the antique (around 1900) meter to measure the current. Nice thing is that you can see it from anywhere in the room. You don't have to use anything complex for a power source for electrolysis. Most folks just use a common garden-variety 5-10 Amp battery charger. Just about any low voltage, relatively high Direct Current source will work. Remember that, at high currents, the process will work faster but more gas and heat will be generated.
For you techno-geeks out there who wonder what I used to make this power supply, the transformer is out of a big, old Hewlett Packard Winchester disk drive that had outlived it's usefulness. The variac (the thing the knob's connected to) simply varies the AC voltage going to the primary of the transformer, thus varying the output voltage. The rectifier consists of a couple of junkbox 75 Amp, 250 Volt silicon rectifiers hooked up in a full-wave configuration. Likewise, the electrolytic (take note) capacitors for filtering the output, the heatsink and almost everything else but the rack and panels are from the same source. Love that junkbox!
"Icky!" or "Yuk!" are probably words my wife would use to describe what the glop in the bucket looks like while it's working. If you let it sit for a day or two after turning off the power source, all the suspended rust will settle the mixture will clear some.
The rail's not a really good test because I'd already gotten most of the rust off of it.
Here's a fish plate bolt I found on the long-abandoned road bed of the defunct Colorado Midland Railroad in the mountains above the town of Buena Vista. Here's a picture of it as I found it. I've ground off some of the rust from the end to make good contact with the negative clip.
Here's the bolt fizzing away. The bubbles are Hydrogen and Oxygen - the reason to have good ventillation when you're doing this. At this point, I'm running the power supply flat-out at a little over 30 Volts and drawing about 5 Amps.
21 January 2005:
This morning, after letting the bolt cook for about 18 hours at low current, I took it out and brushed it off. I also pulled the flywheel out of the bucket and rinsed it off. To my eyes, it looks like the anode (where the rust is supposed to go) has gained more rust than the bolt lost.
That said, do any of you chemists out there know if the Sodium Percarbonate is making the solution too active or something. It seems to work, though.