Carbon fiber reinforced carbon with LOW thermal conductivity 3

[spinda]

Hi folks,
I want to find the CFRC with low thermal conductivity. Most CFRCs are imporved to have high thermal conductivity so I am wondering how much is the least conductivity it can have and where I can get them. Thanks

 

[Compositepro]

How low do you need? You'll find much discussion on how to improve thermal conductivity because composites are very low to start with.
Rayon based carbon fiber is used in rocket nozzles and ablatives because the thermal conductivity is lower than PAN-based. Using a syntacic foam core in a laminate will reduce thermal conductivty through the thickness.
Fiberglass has lower conductivity than carbon.

 

[spinda]

Lower than 0.8 W/mK would be great. I want to use it in a pretty high temperature application (~1000 C). So the properties should remain the same at that temperature. Could you suggest me where I could get them from? Thanks.

 

[Demon3]

Can you specify the shape of the part and the direction that needs low thermal conductivity? As the fibres conduct best along their length, you can tune which direction has high or low thermal conductivity by alignment of the fibres.

Also the thermal conductivity of glass actually increases a lot as you heat it so it may pretty high at 1000C.

Shorter fibres will lower the conductivity but decrease modulus and strength.

There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[spinda]

It would be a ~20"x25" plate (less than half millimeter thick) and direction of low condectivity is through the thickness. We've tried using ceramic at the temperature and it fractured.

 

[Joshmo]

Spinda,

at 1000 deg C tradtional composite materials will not work. Even more advanced resin systems such as polyimide or BMI have Tg's of only 400 Deg C. But, you may be able to use Carbon-Carbon composites which have the resin burned off and infiltrated with carbon. C-C can maintain strengths of 250 to 400 Mpa up to temperatures of 1800 deg C. But, due to the fibers and matrix having higher thermal conductivties, C-C has typical in-plane k values of 50 W/mK for Pan fibers and up to 250 W/Mk for pitch based fibers. But, thru thickness and across ply are usually less than 5 W/mk. Hope this helps and good luck,

J-Mo

 

[RPstress]

For 0.8 W/mK you'll probably need a ceramic matrix rather than carbon. You say a ceramic fractured; was it fibre reinforced? Using silicon carbide fibres like Tyranno or Sylramic might work ok. Pricey, though, but then so's carbon-carbon.

 

[Compositepro]

You may simply need a ceramic or glass with greater thermal shock resistance.

Another approach is to combine an insulator layer with a structural layer.

 

[spinda]

Thanks you all for your suggestion. I got a better idea about the material I want to use.