From: ahahma@polaris.utu.fi (Arno Hahma)
Newsgroups: rec.pyrotechnics
Subject: Re: Does aluminum burn?
Message-ID: <1992Jul3.061153.9276@polaris.utu.fi>
Date: 3 Jul 92 06:11:53 GMT

In article <1992Jul2.224634.29681@hpcvaac.cv.hp.com> billn@hpcvaac.cv.hp.com (bill nelson) writes:

>: Does aluminum burn?  If so, at what temperature is this possible?  I know
>: the stuff melts, but does it actually burn?  The reason I ask is that

>There are a number of variables for burning temperature, such as available
>oxygen concentration, gas pressure, catalysts/retarders available etc.

The most important factor is the particle size. That is, a block of
aluminum is about impossible to get burning, even in pure oxygen. Have
you ever tried cutting aluminum with an oxyacetylene torch like they
do with iron? It is not successful. Al forms a very tough layer of
refractive oxide on its surface and that layer prevents the otherwise
active metal from oxidizing further.

The situation is different, if the aluminum is a fine powder. In that
case, there is a very large surface area to be oxidized. If the grains
are small enough, the oxide layer may never reach its protective
thickness before all of the grain has been expended. Once the powder
is this fine, it really burns easily and fiercely and ignites well.
This can be demonstrated by throwing a spoonful of aluminum dust into
a hot flame (such as oxypropane or oxyacetylene torch). There will be
a tremendous flash and pulse of heat that is quite capable of burning
one's fingers and face (just in case someone tries it ;-).

>Bill

ArNO
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