Thermally conductive, electrical insulator 2

[KevinH673]

I'm sorry for double posting this, as I've already posted this question in the Metallurgy forum; however, this may be a problem who's solution is a polymer.

I'm interested if there is a material I can use in a 1/2" thick piece I have, that will dissipate heat (it is up against a cold plate), yet will electrically insulate. Can anyone recommend anything?

I found a polymer composite with boron nitride coated carbon flakes, but this requires a mold. This piece must be tapped for bolts! I have attached a picture of the part, and where it is mounted, if this helps...

Thank you all.
-Kevin

 

[patprimmer]

It depends on the levels of conduciveness, but aluminium flake is an additive that can increase the thermal conductivity by a bigger margin than it increases the electrical conductivity. As far as I am aware carbon has the opposite effect.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[Demon3]

The absolute best performance is diamond powder. It's the best thermal condustivity there is and is electrically insulating. Diamond powder is not that expensive and can be added to polymer to make the part you want.

If you need lower thermal conductivity and lower cost then use the fillers used in thermal paste.

Alumina Al2O3 or
Hexagonal Boron Nitride


Chris DeArmitt

 

[Pud]

You might be lucky as I guess you only need one piece of material:

http://www.coolpolymers.com/

Otherwise fused quartz, which you have a bit of difficulty tapping!

What is wrong with a slab of aluminium with silicone heat transfer gaskets between and nylon fasteners?

Cheers

Harry

http://www.tynevalleyplastics.co.uk

 

[patprimmer]

Interesting information Chris.

Now firmly locked away in the memory banks.

Kevin

It will require a mould, even if it is a real simple prototype mould that is a bit big and you them machine the moulding to finish it.



Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[Demon3]

It's fascinating that diamond is so electrically conductive and yet electrically insulating. I always assumed it must be super expensive but I have a friend who made super abrasives for 3M and he explained that diamond only gets expensive when it's big enough to be used as jewelry. Diamond powder is not as expensive as you'd imagine.

Also important to note is that the dispersion of the filler and its shape have a huge effect on the thermal conductivity.


Chris DeArmitt

 

[Demon3]

From Wikipedia

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

"Unlike most electrical insulators, diamond is a good conductor of heat because of the strong covalent bonding within the crystal."

"Monocrystalline synthetic diamond enriched in 12C isotope (99.9%) has the highest thermal conductivity of any known solid at room temperature: >30 W/cm·K [ref] five times more than copper"


Chris DeArmitt

 

[unclesyd]

Unless something has drastically changed and based on work that I've been involved in the cost of a small piece of diamond filled polymer would be anything but inexpensive. I would look at a very minimum of 50 times the cost of the base polymer put the cost of a die and if it is more than one the cost of wear and tear on the equipment.

 

[KevinH673]

Thank you all for the suggestions. Diamond is an interesting way to go, I was not aware of it's properties; however, I believe it will be a bit too expensive at the moment.

A nylon, or other electrically isolating fastner with standoffs seems to be the direction I'm leaning, but if I could find a material that is cheap and easily machinable with the properties I need (this almost seems like an oxymoron), it would be even better. Being naive in the matter, that is why I came here.

Chris, would the part be made solidly out of Alumina, or would it be used as an external coating on an Aluminum piece? If so, could it be applied to the fastner threads?

I am interested in using some coatings on aluminum, or as others have suggested in another thread, using Mica sheets. My problem is the electricity still flowing through the threading and fastner.

 

[Pud]

How about something like this:

http://www.stockwell.com/pages/materials_thermal.php

+ Alloy spacer

Fixed with something like these:

http://www.anixtercomponents.com/al...s&language=2&gclid=CI_1uvW11JcCFRE6EAodzlmrCQ

?

Cheers

Harry

http://www.tynevalleyplastics.co.uk

 

[jedward]

hard black anodized aluminum is a god insulator for modest voltages( <~200 volts ) and thin enough to be thermally conductive. use with an insulating shoulder washer to prevent damage by the threads.

 

[HDS]

beryllium oxide

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

http://www.aavidthermalloy.com/products/standard/access/beryllium.shtml