[HH] rust removal

[Tom Metro]

Mark Woodward wrote:
> ...I would use is sodium perchlorate (oxy-clean)
> dissolved in water and a battery charger for electrolytic rust removal.
> It was amazing, connect the electrodes, drop a part into a bucket of
> solution, and in a day, the rust was gone.

Neat. I hadn't heard of using electrolysis for rust removal, but it
makes sense given that you often hear of stray current playing a role
contributing to corrosion.

It might take some digging to find a battery charger that would work for
this. Most modern charger are now microprocessor controlled, and refuse
to output anything unless they detect a minimum battery voltage. (But I
do have an old-school charger with a manual mode that would work.)


> You can google for the exact ratios and stuff.

Here's a video showing the process:
http://www.youtube.com/watch?v=-8vT2mdXBs8

He used Arm & Hammer Washing Soda:
http://www.google.com/products/catalog?cid=14401059783015092671

which Wikipedia says is Sodium carbonate (Na2CO3):
http://en.wikipedia.org/wiki/Sodium_carbonate

rather than sodium perchlorate (NaClO4):
http://en.wikipedia.org/wiki/Sodium_perchlorate

Is the latter better? (One site cautions against using ordinary table
salt, because it can release chlorine gas. NaClO4 seems it would have
the potential to do that. Perhaps the perchlorate sticks together and
remains in the water. The EPA regulates it as hazardous, but as long as
you don't drink the water, you should be fine.)

The other item you need is a sacrificial anode. This video says any
ferrous metal will do, but he recommends stainless steel, and something
with a large surface area. (Comments on some of the similar videos and
in the text documents say don't used SS because it will release chromium
into the water - a toxic heavy metal. Just used some scrap mild steel.)

You then attach the positive to the anode, the negative to your rusted
part, dump both in a bucket of water (keeping the positive battery clamp
out of the water) with 1 tablespoon of soda per gallon of water.

The narrator points out the bubbles coming out of the solution are
mostly hydrogen, so ventilation is recommended. :-)

The end result is metal with a dull black finish. Presumably a good
surface for primer.

Other videos used citric acid, and some using molasseses (which didn't
appear to use electrolysis), plus more using vinegar, apple sider, and
even potatoes (I didn't bother looking at these).

This search:
http://www.google.com/search?q=electrolysis+rust+removal

turns up several text documents describing the technique.

The tail end of this one:
http://www.rickswoodshopcreations.com/Miscellaneous/Rust_Removal.htm

explains the chemistry taking place.


> I imagine you could construct a recirculating continuous stream system
> with a water pump and a tray big enough to catch the return solution for
> objects bigger than can be easily submerged.

I'm not sure that would be effective, as it doesn't sound like it is
merely creating a solution that dissolves rust, but instead depending on
the free flow of electrons from the rusted part to the anode.


I picked up some Evapo-Rust, which I'll try first, as it is more
convenient. But I'll keep the above in mind as a plan B.


Thanks for the tip.

 -Tom