How can silver powder be made both conductive and non-conductive?

[NeoPTLD]

Arctic silver plaste is an example of high silver content silver powder mixture that is an electrical insulator.

CircuitWriter or conductive pen is also made with silver powder, but is conductive.

How do they do that?

 

[CycloWizard]

For electrical conduction, there needs to be a continuous path through the conductor for the electrons to flow. However, for heat to flow easily, it suffices to have a high volume fraction of conductive particles. Thus, if I have a lot of particles in a mixture and I smear it around, there's a good chance that some of them will be touching, but a miniscule chance that a "chain" of touching particles will reach from one end to the other. The chance of forming a continuous electrical path increases as the concentration of silver increases.

 

[PolymerTim]

Definitely a matter of concentration. I did a quick web search and found a few MSDSs that list the major components of conductive silver paints:
http://www.hkwdirect.net/acata...m/datasheets/23711.pdf
http://www.farnell.com/datasheets/23711.pdf

While the MSDS doesn't have to disclose all ingredients, the ingredients they do list consist primarily of silver and volatile solvents. So once the solvents evaporate, you're left with almost entirely silver. I guess the tricky part for the manufacturers was finding a way to suspend the silver particles without leaving any nonvolatiles after evaporation that could affect conductivity between silver particles.

 

[Cogman]

Would a layer of oxidation also add to the non conductivity of silver particles? I would think things like that as well as whatever is used as the solvent would add to the non-conductivity/conductivity of a silver powder mixture.

 

[Howard]

I've heard that silver oxide is also electrically conductive, but I haven't looked too hard for its electrical resistivity.

BeO is fun stuff too. Great thermal conductivity, but very high electrical resistivity.

 

[PlasmaBomb]

Be careful if playing with beryllium... it's toxic

http://en.wikipedia.org/wiki/Beryllium

 

[NeoPTLD]

The Circuit Writer has a bright silver, appearance, while the arctic silver is darker. They both claim to contain silver though. The Arctic Silver is claimed to be made of significant portion of silver. I'm not sure if I agree with the concentration argument, as if you just suspend silver particles in vehicle, you're not going to get good heat conduction either.

 

[CycloWizard]

Originally posted by: NeoPTLD
The Circuit Writer has a bright silver, appearance, while the arctic silver is darker. They both claim to contain silver though. The Arctic Silver is claimed to be made of significant portion of silver. I'm not sure if I agree with the concentration argument, as if you just suspend silver particles in vehicle, you're not going to get good heat conduction either.

It depends on the vehicle and the concentration. There are plenty of polymers which conduct heat well, yet are very good thermal insulators (and vice versa). Even if you use a simple rule of mixtures to assess the mixture's thermal conductivity of, say, 50-50 silver/polymer, the thermal conductivity will be pretty high.

 

[Rabbits]

I really don't care about this as long as they make it work. lol