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Walter Dodson wrote:
> Instead of silver epoxy (to get the billets to the carbon, electrically)
> chop up carbon VERY fine and mix with Hysol. I can't emphasize FINE enough!

Years ago, a ham radio magazine had the tip to use plain graphite powder
(such as for lubricating locks) mixed with epoxy as a conductive bonding
material.  I also seem to recall that he mentioned loading only the
catalyst (hardener) as much as possible as apparently the graphite would
make the epoxy he was using "go off."  I never had the occasion to try
it myself but it seemed perfectly reasonable as a method.  I would
suggest that this might be an easier approach than trying to chop up
carbon fiber as you described, and certainly a lot less messy!  The
mixture would probably only be suitable for conductive connections, as
my guess is that the graphite would not make a good additive from a
strength viewpoint.

While thinking about this, one other additive might be good - both from
an electrical and strength perspective.  That would be nickel powder.
Acheson Colloids makes many conductive paints, several are water based,
like latex paints.  And those come in both carbon and nickel based
formulations.  They're used in EMI (electromagnetic interference)
applications to paint on plastic cases for instance.  The nickel
formulations have much better conductivity and if you pick up a gallon
pail of the paint, you can tell it is significantly heavier because of
the high metallic content.  I cannot remember if they had epoxy
formulations.  Acheson primarily sold to OEMs, but I dug their address
off the web if you're interested in checking with them.
The US URL:
   http://www.achesonindustries.com/main2.html  
Click on "Shielding Coatings" and "CRT Coatings."  From this there do
not appear to be any epoxy formulations, only paint-like products, but
from this site I found out that now they also are in a group of
companies that include: Ablestik Laboratories, Emerson & Cuming,
Tra-con, and Permabond.  The first three were suppliers of electronic
grade epoxies, when I used these kind of products (25+ years ago) many
of which were conductive.  On diving into the sites, the first product I
looked at on the Tra-Con site was TRA-DUCT 2705,
http://www.tra-con.com/products/tpb.asp?product=2705
a nickel filled, 2-part conductive epoxy formulation.  Tra-Con might be
the best of the four choices for conductive epoxies in a reasonable
price range for your purposes as the first two seem to aiming at the
semiconductor applications (read expensive) which require very high
purity and small quantities per device.

It appeared that a distributor or sales rep (for Acheson) might be:
http://www.halltechinc.com/Locations.htm

Charles R. Patton
N360JM
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