From the workshop
Cleaning metal
Photos: Nicole Baxter
Electrolysis makes a meal of rust
by
Josh Giumelli,
KONDININ GROUP
1
Any piece of rusty metal can be cleaned using
electrolysis. The part pictured is an 80-year-old
rusted cylinder head.
2
Find a plastic tub large enough to hold the part.
The tub pictured holds 95 litres and was bought for
$20 from a hardware store.
3
Gather some scrap steel for the anodes and polish
a contact point on the ends. Ensure the whole
surface is relatively rust-free. A third length of
steel is used to support the part being cleaned.
This steel rod becomes the cathode with the rusty
metal part.
4
In this example, two anodes are being used to
increase cleaning efficiency. Arrange them in both
ends of the container as shown.
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R
emoving rust from intricate metal
components and parts can be difficult
but electrolysis offers an effective approach.
Electrolysis removes rust from intricateshaped metal components, which could be
impossible using a wire brush or sand blasting.
Electrolysis is safe and more gentle than an
acid bath because it does not remove any
‘good’ metal with rust.
An electrolysis bath can be easily put
together using inexpensive materials and a
battery charger as a power source.
The chemistry of rust
Electrolysis is a process of oxidation and
reduction. During electrolysis these two
chemical reactions occur simultaneously.
A material undergoes oxidation when
it releases electrons (negatively charged
sub-atomic particles). Reduction is when a
material gains electrons. The process of
rusting occurs when iron oxidises, it initially
losing two electrons, becoming ferrous iron
(Fe2+). If iron loses a further electron it
becomes ferric iron (Fe3+).
At the same time oxygen is being reduced,
gaining electrons and combining with
the ferric iron to become ferric oxide (Fe2O3)
or rust.
How electrolysis works
To clean rust from metal, the processes of
oxidation and reduction are reversed, turning
ferric oxide into magnetite (Fe3O4), which is
an intermediate stage in the rusting process.
Eventually the process of electrolysis turns
ferric oxide into iron metal.
To make the rusting process work
backward, an electrical current is supplied to
terminals called anodes and cathodes in a
conductive solution.
The rusty metal part becomes the cathode,
which carries a negative charge and some
pieces of scrap steel carrying a positive charge
become the anode.
The solution used in electrolysis is a weak
mixture of water and caustic soda (sodium
hydroxide), which conducts electricity far
better than plain water.
By supplying a negative current to the rusty
metal, reduction occurs and the ferric iron
atoms gain electrons, initially reducing to
ferrous oxide. The ferrous oxide then gains
electrons to become ferrous iron.
The anode, which is simply scrap steel,
eventually becomes eaten away by rust.
WARNING:
During operation
hydrogen gas is emitted from the
solution. Place in a well ventilated area
away from flames or sparks.
5
Connect the two anodes together with some scrap
copper wire.
7
Check the rusty part will fit without touching the
two anodes.
6
Attach the part to the rod. The wire needs to make
good contact with the rod and part. An area of the
part may need to be polished back to bare metal.
8
Remove the part and fill the tub with water.
FA R M I N G A H E A D
No. 129
September 2002
Cleaning metal
From the workshop
19
14
9
Add concentrated caustic soda (sodium hydroxide)
to the water at a rate of about one tablespoon per
four litres of water. Stir the solution.
Switch on the power source after all leads have
been connected.
15
10
Place the part into the solution, making sure the
anodes do not contact the cathode (rusty part).
Ensure the battery charger is only supplying
2–4 amperes.
16
11
If everything has been set up correctly, bubbles will
form around the anodes and the rusty part.
Attach the positive lead of the battery charger to
the anode. Make sure no copper parts contact the
solution or they will be eaten away.
When the part has been cleaned sufficiently,
remove it from the bath. The time taken to
clean rusty metal varies. Check the part after about
six hours.
20
Wash the part with water.
21
All loose rust pieces have been removed and the
metal is cleaned by wiping with a rag or wire
brushing. The part will rust quickly if not painted
or oiled.
17
Apart from the reduction of the oxidisation,
hydrogen bubbles are formed on the surface of the
part, which help to remove rust from the surface.
12
22
Parts that are not earthed well such as the spring
pictured will not be cleaned successfully.
Attach the negative lead to the cathode.
18
13
Ensure the battery charger is set to low.
FA R M I N G A H E A D
No. 129
September 2002
After a few hours the liquid will become murky with
white foam on the top. The bubbles contain
hydrogen so place the tub in a ventilated area away
from angle grinder sparks or naked flames.
The two anodes have been shifted, so they are
exposed to different sides of the part.
23
This axe head was placed in the bath for three
hours with the top section (rusty) protruding from
the solution. The middle area was left as treated
and the bottom has been wire-brushed to remove
the black coating. Electrolysis easily removed rust
from the deep surface pits.
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