On Jun 20, 14:31, Chuck McManis wrote:
> At 07:48 PM 6/20/01 +0000, Pete wrote:
> >But aluminium oxide is Al203 and it's a white powder. Or a rather
> >attractive (and, yes, very hard) crystal, known as carborundum, ruby,
> >emerald, amethyst, etc depending on the impurities :-) The only place
> >you'd get AlO2 (which is also white/clear, by the way) is as aluminate
ions
> >in solution.
>
> My aluminum CDs oxidize black, my aluminum sailboat rigging used to,
> (before I got rid of it), aluminum cans that I tried to melt at one point
> also turned into the a black form of the Aluminum oxide powder. Perhaps
> there are other impurities in it that change its color, I don't know, I
> just observe. Now is someone had a classic HP spectrometer I suppose I
> could put this stuff in there and see what it said it was. :-)
It could be aluminium sulphide (I'm not sure if that's black, but it might
be). Or it could be impurities -- neither your rigging nor the cans will
be pure aluminium. In any case, cans usually have a lacquer coating on the
inside, or paint on the outside. I expect the rigging is also reacting
with something from the water (seawater? lakewater? there's all kinds of
stuff in that), but I don't know what. Usually aluminium corrosion is
whitish-grey. I have no idea about the CDs, though, I must admit.
--
Pete Peter Turnbull
Network Manager
University of York
Received on Wed Jun 20 2001 - 17:59:27 BST