Spray-on aluminum finish?

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.

Cheers Trevor Jones

Alodine is probably the easiest process, but it is not a "spray on, wipe off..."

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 thinner...).
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 little...).

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.

Jerry

I've used Everbrite. It too is relatively easily scratched but does not discolor the metal. It keeps the aluminum nice and shiny...

Peter

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.

LLoyd

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. Stealth Pilot

alodine is electrically conductive.

Yep... missed that...

LLoyd

No.

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.

Kevin Gallimore

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.

Dave

you're on the right track. passivate the surface so that it becomes inert and doesnt react.

Stealth Pilot

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 about it