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Old 02-08-2009, 01:08 PM   #1
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Does oxidation cause oxidation

Maybe this should be filed under stupid questions.

If I remove the oxidation off a section of aluminum and all that dust settles on another section of aluminum, clear coated or not will it cause oxidation where it settled.

Same question for rust on bare or painted steel.
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Old 02-08-2009, 01:54 PM   #2
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Is metal dust a miniature life form? A seed? Basically no. Take two pieces of clean steel. Sprinkling rust grindings on one won't cause it to rust. Add moisture, road salt and other factors to the clean piece and it will rust (oxidize).

A cleaned pure aluminum surface doesn't exist for long in our atmosphere. Though not visible, a layer of Al2O3 is formed pretty fast.
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Old 02-08-2009, 02:57 PM   #3
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The oxidation of metals is a self preservation tactic that prevents further environmental deterioration to the exposed surface. It occurs on all metals to some degree, even aluminum and stainless steel. In certain cases, such as with copper, it actually enhances the appearance by creating a desirable patina. As stated in post #2 oxides are not sustainable and do not seed oxidation like plant spores. Oxidation is like an ugly sunscreen if you will. It develops at a certain rate, color, and thickness, depending on the material type and exposure conditions.

Aluminum oxidation starts immediately after the material is formed, cast, wrought, or otherwise produced. Likewise, it instantly begins to reform after polishing. The initial layer is not visible to the naked eye, but it is tenacious. Even a days worth of oxidation can create significant electrical resistance (hence the issue with electrical wiring) and can interfere with the welding of aluminum too.

The good news is that oxide production stops at a certain point, depending on the material type, and the type(s) of exposure. Without it our precious Airstreams would deteriorate to dust in a matter of time. So, we can:

A. Learn to love the gray.
B. Buff and wax, clearcoat, or paint.
C. Switch to SOB.

Don’t lose any sleep over the issue of oxide contamination on your aluminum skin caused by dust from adjacent aluminum buffing. Just wash it off and keep on buffing. Just remember to have a plan to overcoat polished areas in short order. There’s no real need to worry about top coating immediately after buffing, but I would not wait weeks, or months to do it.
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Old 02-08-2009, 04:39 PM   #4
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Thanks for the answers guys

I asked because I took the antenna (Braund Skyliner) off and there was a very thick layer of oxidation under the mounting plate, enough I could scrap big chunks off with a putty knife, it ate through the skin in some places.
Before I put the antenna back up, how do I prep the aluminum so Idon't get this heavy oxidation again?
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Old 02-08-2009, 05:02 PM   #5
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Wink Maybe Something Different.....

Quote:
Originally Posted by bmklawt View Post
Thanks for the answers guys

I asked because I took the antenna (Braund Skyliner) off and there was a very thick layer of oxidation under the mounting plate, enough I could scrap big chunks off with a putty knife, it ate through the skin in some places.
Before I put the antenna back up, how do I prep the aluminum so Idon't get this heavy oxidation again?

Oxidation is one thing....big chunks of stuff may be another issue. If your antenna base is a dissimilar metal, you may be experiencing galvanic corrosion. Galvanic corrosion (reaction) is an undesirable side effect when metals of differing nobility are in contact with each other. The metal of lower nobility will experience galvanic corrosion. Basically becoming a sacrificial anode of sorts. If this is the case make sure you insulate the metals with a gasket, or some type of coating when re-installing.

Best of luck,

Kevin
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Old 02-08-2009, 05:24 PM   #6
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Kevin, you are probably right about dissimilar metals, I had thought the antenna base was cast aluminum but although it is caked with corrosion it does not appear to have affected the base plate at all. I scraped the base plate and now it looks like it has white white dust on it, no pitting at all.
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Old 02-08-2009, 09:56 PM   #7
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I'm not sure if the base of old antennas was white metal. But this issue has been raised by theVAP.com and (I believe) overlander63. There can be significant deterioration of skins under antennas on 1970 units due to the effect bmklawt reports.
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Old 02-09-2009, 05:56 AM   #8
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You need to completely insulate the antenna base. Make a rubber or plastic gasket. Don't forget to put insulating washers under the screw heads and sleeve the screws with heat shrink tubing.
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Old 02-09-2009, 08:04 AM   #9
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What some people call white metal or pot metal is zinc diecastings. Zinc is very high on the galvanic table even higher than Aluminum. It should not cause the aluminum to sarifice itself. I was the materials engineer at Johnson/Evinrude outboard motors and put zinc anodes on our aluminum diecast products to protect them from corrosion in salt water. I do not understand why you experienced corrosion of the aluminum. From what you have observed, it is not likely the antenna base is zinc. The base could be another alloy of aluminum which is lower on the galvanic table and caused the trailer skin (which is either Alclad, pure aluminum or the alloy Airstream is using now). A high silicon diecast alloy which is lower on the galvanic table might make the skin sacrifice to protect the antenna. In any event, the above poster is right that you have to completely electrically insulate between the dissimilar metals to stop the corrosion. Airstream originally used zinc plated steel screws to mount the antenna. The zinc quickly is eaten up and the steel fasteners then become the item the trailer and the antenna tries to protect, causing the castings to start to corrode. The same is true for any steel screw on the trailer. You need to use fresh hot dipped galvanized fasteners and renew then at the first signs of rut at two years or use stainless steel fasteners which are passified to produce a non-conductive oxide layer. When in doubt, insulate and coat with Vulkem between the parts and over the exposed steel.
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Old 02-09-2009, 10:21 AM   #10
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I just recently removed my skyliner antenna from my 75 Tradewind and it also had significant skin corrosion on the skin but not to the extent yours did - there were no spots where the corrosion had eaten through the skin... I cleaned it up best I could and put a nice layer of vulcem between the skin and the new antenna. (as dwightdi suggests in post #9)
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