Note on mag wheels

[Robert Myers]

Your point is well taken, Paul.

Of the common wheel metals (steel, aluminum, and magnesium), magnesium is 
the most flammable.  Perhaps you (and others) might remember a chemistry 
laboratory demonstration in which a small strip of magnesium metal is 
ignited with a burner.  Once the magnesium ignites it burns in air 
(atmospheric oxygen serving as the oxidizer) with an extremely bright white 
flame and produces an immense amount of heat per gram burned.  In fact, the 
heat is so intense that a significant amount of magnesium nitride (Mg3N2) 
is produced by the reaction by direct combination of magnesium and 
atmospheric nitrogen during the combustion.

I don't know how likely it might be actually to produce enough frictional 
heating to cause a magnesium wheel to ignite but if it should happen then 
the energy released would be quite impressive to by-standers.  My gut 
feeling is that a magnesium wheel would be extremely unlikely to ignite 
under anything resembling normal driving conditions.


At 06:15 PM 8/14/01, Paul Meyers wrote:

>Sorry for the WOB, but how could magnesium be its own oxidizer? It's just a
>metal, like calcium or sodium. These are all extremely combustible in air
>(some even at room temperature) under the right conditions, but there's no
>way that they can be their own oxidizer. They don't burn in a vacuum.
>
>Paul Meyers
>Gray 87 5KCSTQ 1.8bar eurolights fuchs boges 146 kMi !
>Pearl 88 5KCSTQ 1.8bar eurolights fuchs bilsteins 2pc-em k24 turbo 128 kMi
>Repainted Pearl 87 5KTQA 1.8bar eurolights TT wheels bilsteins 203 kMi
>Blue 86 5KCSTQ parts car
>
>
>
>-----Original Message-----
>From: Mike Arman [mailto:armanmik at n-jcenter.com]
>Sent: Monday, August 13, 2001 2:46 AM
>To: quattro at audifans.com
>Subject: Note on mag wheels
>
>
>
>
>A quick aside to the lister who asked about magnesium mag wheels instead of
>aluminum "mag" wheels.
>
>Unprotected magnesium corrodes quickly and severely (road salt), and if you
>manage to kerb a wheel and are very unlucky, you can actually set the wheel
>on fire!
>
>Procedure for dealing with a magnesium fire:
>
>Grab everything and everyone important to you.
>
>Exit vehicle.
>
>Retire to safe distance.
>
>Enjoy the show.
>
>
>It will go out when it is all burned up. You cannot extinguish a magnesium
>fire since it is both the fuel and the oxidizer, and it is a VERY hot fire,
>so the damage won't be limited to the wheel, either. Think "road flare" -
>they use powdered magnesium as the fuel.
>
>Best Regards,
>
>Mike Arman
>
>
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Bob
*****
  Robert L. Myers   304-574-2372
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