Letter 139

Why does this derusting trick work?

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I have been removing rust from metal tools by using a galvanized bucket of water and suspending the tool in the water by a string. I connect a twelve volt battery charger to the tool and the other side to the bucket. Overnight the rust turns to black goop which I wash off and further buff out the tool. Works great. I got it from a tip in a wood magazine. Can someone explain why this works. What is the "electrolosis?" process here ? Thank You.

Dennis Slabaugh
Hobbyist Woodworker

the rust on your tools is FeO, of iron oxide, when you run the electricity through the tools the electrons reduce the FeO into Fe and O2, oxygen gas. Every time and equal part of the galvanized bucket which is Zinc is oxidized into ZnO or Zinc Oxide a white powder. So everytime you do this, a little of your bucket is blown away, watch for holes! haha

Adam Hoalcraft
college student - usa

Electrolysis in plumbing,where two dissimilar metals come into contact or electrical wiring comes into contact with water piping creating the process of electrolysis. A definition in this sense how and why the results are caused

Jack Davis
plumbing service - Houston, TX, U.S.A.

It's hard to pick a starting point to explain this without danger of assuming you know something that you may not, or spending pages of explanation starting at too low a level for you. But noble metals like copper want to come out of solution, while base metals like zinc and iron want to ionize into solution.

If you have both an ionic circuit (a wet and salty path between the two metals) and a metal conduction circuit (the metal of the pipe itself if there are no dielectric joints), the fact that the metals are dissimilar means that they form a battery that causes the copper to plate out and the zinc or steel to dissolve.

SOOOO... you want to keep the exteriors clean and dry and insulate the connection between the two metals with a non conductive material if practical. Also, if practical, you want a lot of the anodic material (zinc and steel) and a minimum of cathodic material (copper) so that what galvanic current does flow and will dissolve zinc and steel is divided up over a large surface area.

 
Ted Mooney, P.E.
finishing.com Inc. - Brick, NJ

Getting rid of rust can cost a fortune in chemicals but if you have the time and can fully submerge the item to be de-rusted, here is a cheap way to do it. Submerge it in a black molasses and water solution. 1 part black molasses to 9 parts water. I have 40 litres of the stuff mixed up.
Where I used to work on Norfolk Island (in the South Pacific, halfway between Australia and Fiji - the place where the majority of the descendants of the mutineers from the Mutiny on the Bounty live), we had a 200 litre (44 Imperial gallons, 55 US gallons) drum mixed so we could dip big stuff. Like any small island, because of salt spray, rust is a real problem over there.

Really severe rusting will need a week or so in the solution. I recommend removing the job after a few days and wire brushing to remove the loosened scale, a quick hose down and return to the pot for another go. It is essential that the steel is fully covered. Unprotected steel will corrode very badly at the air/solution interface where it come out of the solution. Note: Some alloys e.g., zinc will be severely corroded by this stuff so keep it for iron and steel only or test it first.

I bought 5 litres of blackstrap molasses (stuff they feed horses) from my local feed and produce store. It is quite cheap.

Ron Beckett
- Emu Plains, NSW, Australia

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