new material for a heat sink

[Heft]

hi there

at the moment we use a copper chrome disk (concave and convex lens shaped) to transfer the heat from a cast iron base to a pyrex cap, the curvature of the cap and the base are different so the copper has a varying thickness.

what is happening is that the caps are cracking, and the coppers expansion is a consideration.

what im looking for are aternatives to the copper chrome, i need a high thermal conductivity and a low thermal expansion.

the caopper insert has at the moment a

COE = 18x10-6/degC
Thermal conductivity = 300w/m degC

any help would be greatly appereciated

 

[kenvlach]

Maybe use something softer than the copper, such as lead or heat-conductive putty. Might not stress the Pyrex as much.
Both are easy to form, so can make thinner than the copper to compensate for lower conductivity.

 

[hacksaw]

looks like you are generating a hot spot in the glass. in that case what you need is to reduce(not increase) the thermal contact.

basically use a lower conductiviy material than copper.

 

[kenvlach]

If the Pyrex cap is breaking due to thermal stress, switch to fused silica glass [it can withstand a quench from 850[sup]o[/sup]C into icewater].

If the Pyrex cap is breaking due to mechanical stress, i.e., from the male copper part expanding inside a female cap, maybe you should change the design. Would a porcelein coating on the cast iron satisfy your requirements (chemical resistance? electrical insulator)?

 

[Heft]

thanks for the replies,

kenvlach, is fused sillica not quite expensive? and porcelin i have not thought about that. interesting

 

[JimMetalsCeramics]

Metals: COE (ppm/C) TC (W/mK)
Molybdenum 5 150
Tungsten 5.5 200
copper-tungsten 8.5 210
copper-molybdenum 7.0 150

Ceramics:

aluminum nitride 4.6 190
silicon carbide 3 130