MadSci Network: Chemistry |
I'm not suprised that a pencil attracts a magnet. Pure graphite can be
made by heating carbon powder, but it comes from mines. I recall that
pencil graphite is also hardened by mixing it with clay ...and the magnetic
properties of carbon depend on impurities as well as upon the crystal
structure. If graphite from a mine has enough paramagnetic contaminants
(such as ferrite, like lodestone,) it will attract more than it repels.
On the other hand, are you sure that the pencil carbon is acting weird?
Some paint pigments are paramagnetic and will weakly attract a magnet. To
assure that it's carbon contamination which causes the attraction, use some
wire cutters to snip the wood off the graphite rod, then experiment with
just the graphite. Perhaps see if the remaining wood and paint will also
attract or repel from a strong magnet.
As a science project you could also try using a blow torch and a fire brick
to burn off the graphite to see how much other stuff is left behind. Pure
carbon burns into CO2, but pencil leads should leave behind some ash which
is possibly magnetic.
Now if you want some REALLY diamagnetic carbon, buy some pyrolytic graphite
from a science hobby supplier. The repulsion effect is so strong that a
small flake of graphite will hover in space above a strong magnet pole.
Pyrolytic graphite
(wikipedia)
http://en.wikipedia.org/wiki/Pyrolytic_graphite
Levitating graphite
(scitoys)
http://www.scitoys.com/scitoys/scitoys/magnets/pyrolytic_graphite.html
Seismometer w/levitating graphite
(M. Lamb)
http://www.geocities.com/meredithlamb/page060.html
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