Longitudinal heat transfer material?

[jjoll]

hi,
I am running some scientific experiments, and I need a sheet of materials that is extremely good conductor of heat in z axis (through its thickness), I mean it is a good longitudinal heat conductor.
I have been doing some researches and some people told me Ni and Mo foils are good at 90 and 138 W/mk but I was wondering if there is something much better. I have found these graphite Sheets (http://www.tglobalthermal.com/t68-artificial-ultra-thermal-conductive-graphite-sheet.php) with 1500 W/mk but they have such conductivity in xy plane only.
I would be grateful if you can point me to the right direction. that would be great if you can show me where i can buy it too.

thanks

 

[mfb]

It would help to know the (approximate) size of your heat conductor. If it is thick enough, you can try to rotate graphite to align it with your heat flow.
Is conductivity along other directions an issue? Copper and silver are very good heat conductors in all directions (~400W/(mK)). Diamond is significantly better, but extremely expensive...

 

[jjoll]

It would help to know the (approximate) size of your heat conductor. If it is thick enough, you can try to rotate graphite to align it with your heat flow.
Is conductivity along other directions an issue? Copper and silver are very good heat conductors in all directions (~400W/(mK)). Diamond is significantly better, but extremely expensive...

thanks, the thickness of this graphite sheet is like 25 um, i don't think it is feasible to just flip them on the side.

 

[christopher.s]

Do you need a material that has good longitudinal (Z) conduction, but lower conduction in other planes? Most materials that I know of that have anisotropic heat transfer tend to conduct well in plane (XY) but not well out of plane (Z). Mica and Graphite come to mind.

 

[mfb]

thanks, the thickness of this graphite sheet is like 25 um, i don't think it is feasible to just flip them on the side.

If you stack 1000 strips of them you have a few cm (not 2.5 as the stack won't be perfect) with a height determined by the width of the strip. This is probably impractical, but I can't tell if you don't say anything about the application where you need the heat conductor.

 

[jjoll]

Do you need a material that has good longitudinal (Z) conduction, but lower conduction in other planes? Most materials that I know of that have anisotropic heat transfer tend to conduct well in plane (XY) but not well out of plane (Z). Mica and Graphite come to mind.

If you stack 1000 strips of them you have a few cm (not 2.5 as the stack won't be perfect) with a height determined by the width of the strip. This is probably impractical, but I can't tell if you don't say anything about the application where you need the heat conductor.

I am trying to thermally print some patterns using a laser CNC machine on some wafer samples. I don't want to apply this vertical laser beam directly on these samples. That is why I was looking for a sheet/foil that goes on top of wafer and thermally transfer the heat to the samples underneath it.

therefore yes, I need a material preferably in the form of a foil that has a very good longitudinal conduction but doesn't vibrate laterally so when laser beam hits it in a vertical fashion it just transfers that heat in a longitudinal fashion as much as possible.
It will also be helpful if anybody can point me toward a solution in which I can use same laterally conductive material to achieve something as I explained.
I already though stacking strips of graphene sheet on their side but due to the very thin nature of these sheets it seems to be a impractical and expensive.

 

[mfb]

What is the target resolution for this process? If it is not significantly below the thickness of a possible sheet, an isotropic heat conduction could work. Aluminium foils are available down to ~1µm thickness, so structure sizes of a micrometer or even a bit less should be fine. Assuming you can fix your foil to the surface with the required precision.