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Oxidation/Corrosion in metal combustion chambers

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Oxidation/Corrosion in metal combustion chambers

Unread postAuthor: broken_system » Mon Dec 07, 2009 7:41 pm

Hey guys, sorry for bombarding you all with my questions but I am near the start date for making my cannon. So here goes:

As you can probably guess from the title I am concerned about long-term use of my cannon and it wearing down, and potentially becoming dangerous if the integrity of the metal is lowered by corrosion/oxidation.

My setup will be a small aluminum or steel combustion chamber (1.8" thick by 3-4" long, by 2" tall), and the barrel will be made of the same metal I choose for the chamber (which as of right now I am leaning towards aluminum).

Without going into much detail I will have a setup that is compact, and able to have a high rate of fire. My projectiles will be small (3/4" max) and lighter (no more than a few grams).

My fuel will be either propane or butane (and due to convenience I am leaning towards Butane).

This is where my concerns come into play. I am not only worried about oxidation from the combustions but also corrosion due to the h2o that forms from the chemical reaction of combusting butane (or propane for that matter).

Am I right to have legitimate concern or do you think that with regular daily maintenance/cleaning that I can remove any chance of the combustion chamber exploding on me after some use.

I am trying to look into oils that I can wipe on the internals to prevent oxidation/corrosion however anyone with experience is more than welcomed to share your knowledge!

Thanks guys!
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Unread postAuthor: kjjohn » Mon Dec 07, 2009 7:54 pm

I have recently done a lot of research on metal pipes since I am going to be building my own metal cannon, and you shouldn't worry about oxidation or corrosion, so long as you use:
a. Galvanized Steel Pipe
b. 6061-t6 aluminum pipe
or c. stainless steel pipe.

Just never use hydrogen fuel in a metal cannon, it corrodes metal very quickly and efficiently.

As for corrosion from h20, these metal pipes were originally intended for, believe it or not, water, so h20 will not cause corrosion, especially in the small amounts produced by butane combustion.
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Unread postAuthor: broken_system » Mon Dec 07, 2009 8:14 pm

Awesome thanks for the info Kjjohn :)
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Unread postAuthor: Heimo » Tue Dec 08, 2009 4:37 am

If you are really concerned about corrosion then the answer is simple paint the chamber on the inside with a rustproofing paint..
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Unread postAuthor: Moonbogg » Tue Dec 08, 2009 6:58 pm

I left my aluminum cannon outside on a gun table overnight and it was soaking wet from mist by the morning. It didn't rust and never will. The cannon did not explode into a violent mess of chaotic blood spilling goop. I am a scholar in wordiness.
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Unread postAuthor: broken_system » Tue Dec 08, 2009 11:31 pm

Moonbogg wrote:I left my aluminum cannon outside on a gun table overnight and it was soaking wet from mist by the morning. It didn't rust and never will. The cannon did not explode into a violent mess of chaotic blood spilling goop. I am a scholar in wordiness.


Haha thats awesome, chaotic blood spilling goop :) Well thats good that there is not cause for concern, better safe than sorry!
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Unread postAuthor: F.E.A.R._Sniper » Wed Jan 13, 2010 2:07 pm

Moonbogg wrote:I left my aluminum cannon outside on a gun table overnight and it was soaking wet from mist by the morning. It didn't rust and never will. The cannon did not explode into a violent mess of chaotic blood spilling goop. I am a scholar in wordiness.


i dont wanna be that guy but in order to protect the gene pool of humanity i have to.

of course it didnt rust, there is a reason for that. ALUMINUM DOES NOT RUST. it will oxidize to a degree but nothing major on the scale of structural failure for many years. annodizing is a coating that can be applied to any aluminum and if applied correctly it will prevent any oxidation that would otherwise occur with aluminum
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 13, 2010 2:13 pm

F.E.A.R._Sniper wrote:of course it didnt rust, there is a reason for that. ALUMINUM DOES NOT RUST. it will oxidize to a degree but nothing major on the scale of structural failure for many years. annodizing is a coating that can be applied to any aluminum and if applied correctly it will prevent any oxidation that would otherwise occur with aluminum


Isn't anodising the build-up of an oxide layer anyway?
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Unread postAuthor: F.E.A.R._Sniper » Wed Jan 13, 2010 2:15 pm

i believe you may be right, but it would be a controlled and in most cases colored oxidation
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Unread postAuthor: jimmy101 » Wed Jan 13, 2010 2:30 pm

F.E.A.R._Sniper wrote:...of course it didnt rust, there is a reason for that. ALUMINUM DOES NOT RUST. it will oxidize to a degree but nothing major on the scale of structural failure for many years. annodizing is a coating that can be applied to any aluminum and if applied correctly it will prevent any oxidation that would otherwise occur with aluminum

You are wrong.

Aluminum does rust. Indeed it rusts faster than does iron, copper, ... just about all other metals. (Using "rust" as being the oxide of a metal.)

Annodizing isn't "applied" to Aluminum. Anodizing is controlled oxidation, so it is "controlled rusting" of aluminum and is a process done to aluminum not something that is applied.

All pieces of Al have a surface layer of rust. If the surface was not anodized then the rust layer is not real strong but it is strong enough to protect the underlying Al. Usually you can take a piece of Al and use it as a pencil and create a gray line on paper for a while. That line is the Al2O3 layer rubbing off. The fresh Al surface will be recoated with oxide pretty quickly.

The difference between Aluminum rust (Al2O3) and iron rust is that the Al2O3 is compatable with the crystal structure of Al. The coating of Al2O3 essentially seals the Al and prevents further oxidation. Iron (and steel) on the other hand is not compatable with the iron oxides (Fe2O3 and FeO). The surface layer of rust does not adhere well to the underlying iron since the crystal structures are different. The result is that the surface layer of oxide flakes off allowing oxygen to get to the unoxidized metal below the layer. Eventually the iron will be completely converted to rust.
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Unread postAuthor: john bunsenburner » Wed Jan 13, 2010 3:20 pm

A good example of aluminium rusting is when aluminium has its protective layer removed by mercury, if it then exposed to air(the title is wrong, the mercury isn't reacting to form what you see, oxygen in air is):

[youtube]http://www.youtube.com/watch?v=Z7Ilxsu-JlY&feature=fvw[/youtube]
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