HP-2116A chassis (or repairing cast aluminum)

Pete Turnbull pete at dunnington.u-net.com
Sun Apr 17 12:37:19 CDT 2005


On Apr 17 2005, 12:19, Teo Zenios wrote:

> Pure magnesium ignites at 476 C and burns at 2200 C so if the case is
pure
> enough (doubtful, additives change the burning properties) and you
get it
> hot enough then good luck trying to put the fire out.

That temperature is for powder or dust.  It's much higher for bulk
solid magnesium, normally quoted as 625C or thereabouts, though lower
than its melting point (648C).  There are various factors that affect
ignition temperature.  See for example:

http://www.netl.doe.gov/coolscience/res_archive/q&a_36.html
http://www.eh.doe.gov/techstds/standard/hdbk1081/hbk1081c.html

and for common alloys:

http://www.parkwayproducts.com/thixomolding/engineering_data.html

Oh, and for some more pictures of what happens when it does burn, and
how hard it is to make that happen:

http://www.theodoregray.com/PeriodicTable/Stories/012.2/

By the way, titanium dust and grit is worse than magnesium dust; when
turning titanium you're supposed to use water-based collant to avoud
ignition risk -- but it's only a few months ago I had my titanium
spectacle frames welded back together.  Aluminium too; damp aluminium
dust will spontaneously ignite (another standard school chemistry demo,
it used to be mixed with iodine to produce purple smoke) and its bulk
ignition temperature is lower than that of magnesium's, but I've seen
its auto-ignition temperature quoted as high as 780C.  I suppose the
reason I've replied to so many of the posts about this is that people
remember seeing magnesium ribbon burning in school chemistry classes,
but Real Life ain't like the science lab.



-- 
Pete						Peter Turnbull
						Network Manager
						University of York



More information about the cctech mailing list