I could swear somebody told me about some sort of oxidizing spray-on/
wipe-off type of solution that can be used on aluminum. I'm looking
for a simple way to give a basic protecting finish to brushed
aluminum, which also doesn't inhibit electrical continuity. Anodizing
or painting is a little more than I want to deal with. Anybody heard
of something like this?
Thanks for any info,
To protect aluminum with a spray on/wipe off product, alodine is the
only thing that comes to mind. It discolors the surface, though.
Pretty much anything you do to aluminum, including leaving at alone on
the shelf will affect its electrical properties, as the oxide layer that
forms on the surface of aluminum offer a higher resistance.
That was a good part of the problem with Al. wiring in houses.
Alodine seems to be the only solution that does not require paint or
tanks of chemistry.
alodine is electrically conductive.
anodising electrically insulating.
you can get alodining kits at pilot shops on your local airport.
or through aircraft spruce and specialty or wicks mail order.
if you leave alodine on too long it will appear brown but a light gold
finish passivates the surface almost as well.
Alodine is an insulating conversion coating. Sometimes you will see a
reference to a "level 3" alodine coating for applications (such as
aircraft) that require conductivity. The level 3 coating is so thin that
very small forces will scrape through the conversion layer. You can test
this at home.
The reference for alodine conversion coatings is MIL-C-5541.
Alodine is probably the easiest process, but it is not a "spray on, wipe
Alodine is available at automotive paint stores. It comes in two kinds,
gold, which will turn the aluminum sort of a straw-yellow, and silver, which
discolors it only slightly. Either will inhibit oxidation and ensure
continued electrical conductivity. But the alodine layer is extremely thin
and can easily be scratched through...
The way I do it is a three step process:
1. Thoroughly de-grease the piece of aluminum (I wash it in laquer
2. Immerse the part in a solution of phosphoric acid (which you can get
anywhere they sell alodine) for three to five minutes. Rinse.
3. Immerse the part in the alodine solution for a few minutes (time will
vary with temperature). Rinse and dry.
The chemicals are relatively harmless. You don't have to worry about
getting on yourself (just rinse it off...) nor need you worry about fumes
unless you are doing large items (the phosphoric acid outgasses a
The only tricky part is the time you leave it in the alodine: too short and
you don't get good coverage and too long and you will turn the aluminum a
rather crummy shade of brown...
The chemicals are not cheap, but not that expensive, either. About $25 will
get you a pint of each and a pint will do a LOT of aluminum... And the
shelf-life is several years.
Nothing you can do to aluminum will perserve surface conductivity, unless
you plate it with a non-corrodable metal, like platinum, gold, or chromium.
Aluminum, almost instantly upon being cleaned, begins to form an aluminum
oxide (like sapphire) coating that is an excellent insulator.
Thanks for all the help guys. This is for antennas... They actually
work fine without anything done to them at all. You can avoid problems
by just taking them down and cleaning them every so often. But I was
just looking into ways of getting around that, if possible.
On Feb 18, 11:44 am, email@example.com wrote:
Wiping clear polyurethane (non-metallic) paint is really probably the
easiest way to go, it's rf transparent and very durable. If you need
something more serious, you might want to see Henkel 5700, (Alodine
5700) but if it's a salt water application I think you have to use a
chromium product. The proper prep is really time consuming so, if it's
like some home patch antennae or something I wouldn't be too troubled
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