I couldn't seem to get into the electrolysis FAQ site suggested by Buzz (I'll try again
later). But if anyone wants to know more about electrolysis for converting rust, you might
do well to look at these sites:
Conserving a corroded iron cannon (very interesting):
http://www.pch.gc.ca/cci-icc/english/treatmen/cannon.htm
Possible conservation approaches for a civil-war-era submarine project (also interesting,
discusses several conservation options for iron/steel):
http://www.cla.sc.edu/sciaa/hunley3.html
The chemistry of corrosion:
http://c.chem.ualberta.ca/~plambeck/che/p102/p02115.htm
Notice that I said "converting" not "removing" rust. The electrolysis process converts
typical "rust" to magnetite, which is also an iron oxide, but it's a MUCH more stable
oxidation state.
The nice thing about electrolysis for treating deep rust, as opposed to chemical "rust
stop" surface treatments, is the depth of treatment that can be obtained. It also helps
eliminate salts like chlorides, which greatly speed up the rusting process.
However, don't expect all of your rust to fall off, leaving gleaming metal. You'll still
have iron oxide, except it will be more stable, and kind of a blackish color. Sometimes
the electrolysis process will help loosen surface agglomerations so that the profile of
the object will more closely resemble its original shape after treatment.
In archaeology classes, we used to clean up and conserve small iron (and other metal)
artifacts using electrolysis with a sodium hydroxide solution. One thing I recall about
this process is that it was excruciatingly SLOOOOOW. It often took months to do something
as small as an iron door hinge. But the hinge or other object did look pretty good
afterwards (black...not bare metal).
For removal of minor surface rust, phosphoric acid works quite well if you don't want to
sandblast or hot tank the object. Be careful not to leave the metal in too long, since it
also etches the clean metal...and neutralize the object afterwards. Also be EXTRA careful
with iron, especially cast iron, since it's porous and an acid treatment might weaken the
surface layers. In fact, I personally wouldn't even consider acid rust removal on iron.
I'm not really sure about the effects of hot tanking cast iron in caustic soda or other
solutions, either. Check it out before you accidentally destroy a valuable part.
Aluminum oxide or silicon carbide blasting will do a good job of removing rust and
preparing the surface to bond with paint, since it makes countless microscopic sharp
facets on the surface of the metal that really give primers a good grip on the metal.
Glass beads tend to make tiny rounded indentations that don't work as well for holding
paint. A self-etching primer will largely make up for an overly smooth metal surface,
however, providing a good grip on clean metal.
My suggestion as to electrolysis? TRY IT FIRST on four small pieces of rusted steel, each
with a different condition:
- Clean, but with light surface rust.
- Clean, but with some heavy, deep rust.
- Light surface rust, but with paint over the rusted area.
- Heavy, deep rust with paint over the rusted area.
Here I go, getting long-winded again. Time to stop procrastinating and get back to work...
Alan
Jeep Meister wrote:
> I have been following the comments here on chemical dipping and would like
> to suggest a method for rust removal using electrolysis. On the web site at
> http://acheron.watson.ibm.com/~clarke/woodwork/electro.html
> I found a FAQ
> on rust removal using electrolysis by Ted Kinsey. It took me several tries
> over a few days to connect to the web site so be patient.
> The process seems simple enough and uses a tablespoon of washing soda (Sal
> Soda) to a gallon of water and a 12 volt battery charger. I haven't tried
> it yet, but saw a show on TV where they used something similar to restore
> artifacts from sunken ships. A friend has a rusted GPW chassis that we hope
> to try it on. We plan to make a large tank out of plywood and 2x4's, lined
> with vis queen to make it water proof, and then treat the entire chassis at
> once.
> I know this process doesn't do a thing for paint removal but it sure sounds
> like a good alternative to sandblasting large complex parts for rust
> removal. If you can't get into the web site email me and I'll email you the
> FAQ in .txt form.
> Buzz
>
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