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Can we make conductive epoxy?

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Patrick

Sat Oct 01 2011, 05:48AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

CAn we make conductive epoxy ourselves, or are we stuck having to buy the silver epoxy for mucho $'s ?

I was thinking of loading epoxy with copper particles, has anybody done this? Also the silver epoxy i bought recently claims 0.38 ohm-cm rho, but i could live with much more resistance in most cases, so im wondering if the silver component is really needed.

Conundrum

Sat Oct 01 2011, 10:20AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Yeah, I made this work using RTV tyre repair adhesive and graphite lock lubricating powder.

Silver particles can be made using an ultrasound cleaner and silver gilding foil..

Kind regards, -A

Proud Mary

Sat Oct 01 2011, 12:44PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Conductive Particulate to Dielectric Ratio and Resistance - something to think about!

A girl has an epoxy puddle 100mm across, and just ten silver spheres of 10mm each to form a conductive bridge across it. Clearly, for conduction to occur, the ten spheres must be in a perfectly straight line passing through the centre of the circle.

Now suppose she has 100 x 10mm spheres and throws them at random into the dielectric puddle. What is the probability that a conductive path will be formed across the puddle on any one random arrangement?

Suppose one single conductor chain has insufficient current carrying capacity so that two or more chains must exist in parallel?

In practice, there are likely to be 3-D chaotic combinations of series and parallel conductors. It's not too hard to imagine a lowest possible resistance scenario, where one direct straight conduction route has all the other available conductors in parallel with it, but what of the maximum possible resistance, a maze within a maze?

In the absence of a solution of sufficient elegance, pack as much metal as you can into the epoxy - quite possibly easier said than done.

Pinky's Brain

Sat Oct 01 2011, 12:55PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

Carbon black is a lot cheaper.

Patrick

Sat Oct 01 2011, 04:52PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Proud Mary wrote ...

In the absence of a solution of sufficient elegance, pack as much metal as you can into the epoxy - quite possibly easier said than done.

I calculated that for 38 USD i get 14 grams of silver epoxy, which at a density of 2.34 g/cm^3 means:

14 g / 2.34 g/cm^3 = 6.0 cm^3 of cured epoxy,
so 6.0^(1/3) cm^3 = a cube 1.8 cm on each side.
or 0.366^(1/3) in^3 = a cube 0.72 inches on each side.

Thats quite abit so ill use it wisely and hope i dont need much, if i do find a solution to this problem it would need to cost less than 38 USD per 14 grams to be a useful pursuit. I like the graphite lock point...

Silver epoxy

Shrad

Sun Oct 02 2011, 08:40AM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

I once bought 100Âµ red copper powder and 200Âµ aluminium powder, and they were relatively cheap on ebay ($5 per 200gr. if I recall, pyrotechnics use)

it should be easy enough to mix an adequate ratio of copper and another metal or metal oxyde to obtain proper channel repartition (like hyperfine silver powder, say 50Âµ, in a small quantity to fill holes in a 200Âµ copper/epoxy medium)

Pinky's Brain

Sun Oct 02 2011, 12:39PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

The exact structure of the powder is important, the more filamentary the lower the loading needs to be. Also settling can be a problem.

Lots of experimentation necessary.

Patrick

Sun Oct 02 2011, 03:51PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Ill look into buying metal powder, but for now ill use the silver epoxy i just bought.

Proud Mary

Sun Oct 02 2011, 04:28PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

It would be interesting to make a point-and-plane spark gap out of silver-loaded epoxy, and examine the discharge surfaces under a microscope after firing single shots.

Patrick

Sun Oct 02 2011, 04:31PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Proud Mary wrote ...

It would be interesting to make a point-and-plane spark gap out of silver-loaded epoxy, and examine the discharge surfaces under a microscope after firing single shots.

Ill leave this task to someone who has the opitical tech for the job, Proud Mary.

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