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 Post subject: Expansion of Aluminum
PostPosted: Fri Aug 31, 2012 6:33 am 

Joined: Tue Feb 17, 2009 11:04 am
Posts: 37
I understand that copper will expand up to 67,000 times when vaporized. Does anyone have a number for the expansion of aluminum?

Thanks!


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PostPosted: Fri Aug 31, 2012 5:47 pm 

Joined: Fri Aug 31, 2012 5:37 pm
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Thank you for posting this for me this morning, I just registered as a member. So far I'm finding between 40-44k, however I have also found information for aluminum as fuel, therefore I don't know if aluminum should be a concern for expansion as much as fuel for the explosion. The more I research the more questions I have.


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PostPosted: Mon Sep 03, 2012 10:04 am 
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Trpotter wrote:
Thank you for posting this for me this morning, I just registered as a member. So far I'm finding between 40-44k, however I have also found information for aluminum as fuel, therefore I don't know if aluminum should be a concern for expansion as much as fuel for the explosion. The more I research the more questions I have.


First off, there is usually plenty of aluminum in jewelry boxes. Aluminum oxide is a mineral. The colored forms are called sapphires, except one in particular. The red colored ones are called rubies. That's the reason that anodized aluminum (aluminum that has been purposely oxidized heavily to form a protective coating) with the right impurities forms an extremely pretty color of blue or red.

Not that it makes much difference but aluminum is an excellent fuel source! Aluminum readily oxidizes under all conditions. Powdered aluminum is used in manufacturing fireworks, military smoke bombs, and "thermite" demolution agents for it's fantastic properties as a fuel. Aluminum is highly exothermic when it is burning.

That being said, high temperature chemistry is kind of strange. With the major exception of carbon, nearly all compounds especially metals lose their affinity for oxygen. The temperature dependence is typically shown on an Ellingham diagram. Here's a link to one:
http://www.docbrown.info/page03/3_51energy/ellingham1.gif

Notice that unlike ALL metals, carbon has the nifty property that it becomes much more reactive with oxygen (turning into CO) as temperatures increase. All that it requires to convert a metal oxide into pure metal is to get to a high enough temperature and have some carbon around as long as you have a blanket of some kind of liquid (aka slag) on top to prevent everything from leaching oxygen out of the air. The resulting CO boils off and has to be burned seperately to avoid poisoning the smelter crew.

Also notice that this only happens at 2500 Kevlin degrees which is over 4000 degrees Fahrenheit. Coal/air flames only get to about 3500-3800 F maximum. So to actually smelt aluminum you need something much hotter than required for steel or copper or other metals. The choices are limited to either pure oxygen/fuel or else electric arcs. The process that is actually used is to literally drive an electric arc through a molten bauxite (aluminum oxide)/cryolite mixture. The electrodes are made out of pure carbon and are continuously cast and consumed by the process...which is the source of carbon. Needless to say, the cost of producing aluminum is almost entirely driven by the cost of electricity. This process is six times more expensive to operate than making steel and the price increase is entirely due to the extra energy needed.

The only thing missing from the above diagram is that it is just a tad too simplified. What it's not showing is the point where the various metals melt and then boil. This diagram is much harder to read but shows how the melting and boiling points fall on the chart:
http://www.industrialheating.com/IH/2004/02/Files/Images/99306.jpg


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PostPosted: Fri Sep 07, 2012 12:59 pm 
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Joined: Sat Nov 21, 2009 10:23 pm
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I investigated an arc flash that started within an 800A aluminum bus duct. The end result was a fatality. A four foot section of the bus actually burned free and dropped to the floor. The electrician was approximately fifteen feet off the floor in a scissors lift. His shoes stayed on the platform and the body ended up approximately fifteen feet from the base of the lift. The problem started when the electrician tried to insert a bus plug, the entry angle was off and the outside male stab on the plug hit the outside female phase stab of the bus duct and the bus duct case.


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