[alfa] Re: alfa-digest V9 #860

[George Graves <gmgraves@xxxxxxxxxxx>]

While old photographic flash powder was magnesium, as are road flares, 
the flash properties of the powder and the burn characteristics of the 
road flares have as much to do with the form of the magnesium as it 
does the fact that it is magnesium. The flash powder was ground to a 
talc-like consistency which made it easily mixed with oxygen This is 
what made it so highly combustible. Flares are a mixture of a similar 
magnesium powder and an oxidizer (chemical oxygen source) which 
controls the speed of the burn. Remember, even ordinary wheat flour 
will burn at a rapid pace when mixed with air in the correct 
proportion. There are many stories of half-empty grain silos and flour 
mills actually violently exploding because the flour or wheat 
particulate in the air came in contact with a combustion source as 
innocent as a static electricity discharge or an electric light switch 
arcing on contact. Yes, magnesium will burn -especially in  powder 
form. So will aluminum powder. But there is little chance of so-called 
"magnesium" wheels catching fire for a number of reasons, not the least 
of which is that virtually all of these wheels are an alloy of 
magnesium and aluminum and thus are NOT pure magnesium. I would think 
that pure magnesium, though certainly light, would be simply too soft 
to make a structural component like an automobile wheel. Secondly, the 
mass of a wheel made of pure magnesium would be such that it would take 
one hell of a heat source to heat it to it's flash point. A heat source 
not found automotively in anything short of a burning car, in which 
case, the wheels are least of one's worries anyway. BTW, flash-bulbs 
work on a different principle than flash powder. They work due to 
electrical incandescence. I.E. a high current is passed through a very 
thin metallic substance (usually, aluminum filament) in the bulb. The 
current heats the metal up almost instantly to the point where it 
literally vaporizes giving off an intense light while doing so 
(somewhat like an ordinary light-bulb when it burns out).

George Graves
'86 GTV-6 3.0 'S'


On Thursday, October 9, 2003, at 02:26 AM, alfa-digest wrote:


> Date: Thu, 9 Oct 2003 00:39:58 EDT
> From: TWFAUST@domain.elided
> Subject: Re: [alfa] Re:  Refinishing Magnesium Wheels
>
> In a message dated 10/9/03 12:17:07 AM Eastern Daylight Time,
> webb.p@domain.elided writes:
>
> > Aren't magnesium wheels prone to leak if not painted or otherwise 
> > treated?
> > And I think I read something about them being able to catch fire.
> >
> > -Peter
> Magnesium can be porous, but except for between the beads, I don't see 
> where
> painting will help. Magnesium burns at a rather low temperature. If I 
> remember
> correctly, old photographic flash bulbs and flash powder were magnesium
> composites. I wouldn't worry about wheels bursting into flame at road 
> temperatures.
> Tom Faust
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