>One more technique for removing rust is Electrolytic Rust Removal. Rust can
>be electrically etched off of iron or steel in a bath of mild alkali, such
>as Sodium Carbonate (swimming pool supply stores. Ask for product to raise
>water pH). Connect the rusty part to the negative terminal of a 12V battery
>or battery charger and a scrap piece of steel or iron to the positive
>terminal. Use one tablespoon of Sodium Carbonate per gallon of water. This
>technique has many advantages. First, the alkaline solution is much safer
>than some of the acids mentioned above. It is still a chemical, so rubber
>gloves and splash goggles are recommended. Another advantage of
>electrolytic rust removal is that it will have no effect on good metal, so
>you can leave the work in the bath for a long time and not damage the
>metal. There is no risk of hydrogen embrittlement nor of etching unrusted
>metal.
There are a few problems with this method, although they don't always show
up. The process doesn't "remove" rust, it reconverts it to metallic iron.
This may seem like a good thing, but there are some hidden problems in
that process. The redeposited iron is "spongey" - it has a much lower
density than forged iron, and is semi-porous. It rusts much more quickly
than forged or rolled plate. That means it is important to protect it
ASAP. This is especially important when the car might be exposed to salt
or weak acids, since there is a horrible process whereing the ions
catalyzes rusting. That means that once the rust restarts, it continues
into good metal at a faster rate.
This was discovered not in automobiles, but in the care and preservation of
antiquities! The process of electrolytic cleaning became very popular in
the early 20's, and many items had been cleaned by the late 30's. As the
war approached, many items were removed from the British Museum, stored in
boxes filled with pine shavings, and stored in deep mines safe from bombs
and such. However, much to the horror of the keepers, many of the items
which had been electrolytically cleaned were found to be mere piles of
rust, verdigris, or other metallic oxidation products after a mere 6 years
of storage. Most of the other objects were hardly damaged. It was tracked
down to the combination of the spongy redeposited metal and the organic
acids in the pine shavings. Many priceless artifacts were lost.
There are other problems with this technique, which almost certainly
wouldn't show up in cleaning MGB parts. For example, ancient iron
artifacts which had been almost completely converted to rust were cleaned
by this technique, and converted to an increadably fine matrix of
filiments. Sort of like super fine steel wool. Normally steel wool
doesn't burst into flames, because the iron already has a thin coating of
rust. This thin oxide coating protects some metals (like chromium and
aluminum), and slows down subsequent rusting of iron. However, these
freshly cleaned objects had huge surface areas of virgin iron. When these
objects were taken from the bath and the water began to evaporate, the heat
from the sudden oxidation could actually cause some of them to burst into
flames. Ever burned steel wool? Try it, and you'll get an idea of the
horrifying site of a 10'th C viking sword actually bursting into flames!
Anyway, I ramble... the take home lesson is this - electrolytically
cleaned surfaces are more prone to subsequent oxidation, and in the
presence of some acids or salts, can actually work to catalyze the
destruction of surrounding once-solid metal. Caveat emptor!
By the way, if anyone has any questions on preservation or restoration of
antiquities (and I don't mean T series MGs, I mean ranging from 1000 to
4000 years old) please feel free to drop me a line.
---
A .sig is static My life is dynamic. I can't think of a single
quote or witty saying that expresses the mercurial nature of the changes in
my life. The only constants in my life are stress, my loving wife, and
the weekly hairball my cat leaves on the carpet.
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