Why no Copper powder based Thermal Pastes?

[made2hack]

Hey,

Wondering why you typically can't find Copper based thermal pastes? The thermal conductivity while not as high as Ag is close to twice that of Al, yet Al and Ag are the most common fillers in thermal paste (aside from some kind of ceramic or diamond).

Any ideas?

[RobertHolcombe]

"Silver is the most conductive of all the commonly available metals and is relatively willing to enter a state of fluidic suspension. Although copper is another choice, it does not enter a suspended state as readily and is harder to work with."

http://www.vanshardware.com/articles/2001/december/011209_AS_Interview/011209_AS_Interview.htm

[made2hack]

Thanks for the link.

If you are not blinded by the 1994 style of yellow text on black background, it is a pretty interesting read.

[T3sl4co1l]

I've seen copper loaded anti-seize used for thermo-electrical transfer.  No idea how well it worked, probably better thermally than electrically.

Tim

[SeanB]

I've seen copper loaded anti-seize used for thermo-electrical transfer.  No idea how well it worked, probably better thermally than electrically.

Tim

More there to prevent corrosion in the interface of bus bars from causing failure than for electrical or thermal improvements. It just keeps the bare shiny copper bar sections looking like good clean bus bar sections for decades, otherwise after a few years of heating there will be an oxide layer there, which will increase contact resistance slightly. If you have 1kA flowing in this join even a doubling to 2mR will give a signifigant increase in power dissipation.

You can but copper based compounds, just go to the auto parts store and ask for Copaslip. Works as a heatsink compound and is quite good, you just use a small blob and spread it out with a plastic spatula over the heatsink. Just note it is not a very good conductor, but is definitely not classed as an insulator.

[wkb]

I've seen copper loaded anti-seize used for thermo-electrical transfer.  No idea how well it worked, probably better thermally than electrically.

Tim

More there to prevent corrosion in the interface of bus bars from causing failure than for electrical or thermal improvements. It just keeps the bare shiny copper bar sections looking like good clean bus bar sections for decades, otherwise after a few years of heating there will be an oxide layer there, which will increase contact resistance slightly. If you have 1kA flowing in this join even a doubling to 2mR will give a signifigant increase in power dissipation.

You can but copper based compounds, just go to the auto parts store and ask for Copaslip. Works as a heatsink compound and is quite good, you just use a small blob and spread it out with a plastic spatula over the heatsink. Just note it is not a very good conductor, but is definitely not classed as an insulator.

Copaslip is also very neat stuff for steel bolts going into aluminium threading.  Like on a motorcycle.  I got this tip like 30 years back from the mechanic working my bike.  It prevents aluminium oxide turning these bolts into "will never ever let go" fasteners.

Really recommended!

Wilko

[Clear as mud]

I'm currently working on a motorcycle with a bolt broken off in the aluminum engine, and I would like to avoid it happening again in the future.  So, Copaslip?  Will any copper-based anti-seize compound work just as well?  I'm not sure if I have seen that brand before, and not sure if it is available here.

[T3sl4co1l]

Nickel based anti-seize is also popular.  Not sure what the difference is, really.  I suppose nickel will be more corrosion resistant than copper, so that's one thing.

Tim

[SeanB]

There is also a Loctite white releasable threadlock that only keeps the thread clean, which will also work. Used in outboard motors to protect bolts in the engines.

[LabSpokane]

I'm currently working on a motorcycle with a bolt broken off in the aluminum engine, and I would like to avoid it happening again in the future.  So, Copaslip?  Will any copper-based anti-seize compound work just as well?  I'm not sure if I have seen that brand before, and not sure if it is available here.

Copper anti seize is available at any decent auto parts store for a few bucks. Permatex is one common brand. Highly recommended for any dissimilar metals.

[SeanB]

Nickel based anti-seize is also popular.  Not sure what the difference is, really.  I suppose nickel will be more corrosion resistant than copper, so that's one thing.

Tim

Nickel based ones are used with stainless steel fasteners or stainless steel substrates. The copper causes fretting corrosion at high temperatures with stainless steels, which the nickel reduces. with titanium pretty much all cause fretting corrosion, as they tend to melt.

[Ian.M]

There's also anticorrosive jointing compounds like Duralac: http://www.llewellyn-ryland.co.uk/downloads/duralac.pdf which is the marine industry 'gold standard' for dissimilar metal permanent fastenings into aluminium and other light alloys.  (for frequently removed fastenings, a Teflon loaded grease is preferable).   Copper loaded anti-seize is generally a bad idea for fastenings in aluminium and light alloys if there is significant salt water exposure due to the high risk of galvanic corrosion.  The only common anti-seize that's worse is graphite grease.   

I'd be reluctant to use copper based antisieze on an external bolt in an aluminium engine block exposed to road spray if your municipality uses a significant amount of salt on the roads in the winter.

Back to the original topic: I suspect that the reason you don't commonly see copper or aluminium flake based heatsink compounds is marketing.  Silver loaded compounds can easily be marketed as a premium product even though the advantage over Zinc oxide or Alumina loaded compounds is fairly marginal.

[f5r5e5d]

you can get diamond powder filled thermal grease too today

pyrolytic graphite sheet has applications in 2D heat spreading

[SeanB]

There's also anticorrosive jointing compounds like Duralac: http://www.llewellyn-ryland.co.uk/downloads/duralac.pdf which is the marine industry 'gold standard' for dissimilar metal permanent fastenings into aluminium and other light alloys.  (for frequently removed fastenings, a Teflon loaded grease is preferable).   Copper loaded anti-seize is generally a bad idea for fastenings in aluminium and light alloys if there is significant salt water exposure due to the high risk of galvanic corrosion.  The only common anti-seize that's worse is graphite grease.   

I'd be reluctant to use copper based antisieze on an external bolt in an aluminium engine block exposed to road spray if your municipality uses a significant amount of salt on the roads in the winter.

Back to the original topic: I suspect that the reason you don't commonly see copper or aluminium flake based heatsink compounds is marketing.  Silver loaded compounds can easily be marketed as a premium product even though the advantage over Zinc oxide or Alumina loaded compounds is fairly marginal.

I remember that for aircraft sheet metal. It went by the nickname of "ducks**t", as it was sticky, smells and looks like that. Fun is to try to get a strut out that went in 20 years ago with that. No corrosion, just the very dry gunk keeping the 2 parts together. Paint it on, put the panels together then start with the dolly and the rivet hammer to set all those solid rivets.

I got good at using a small ball peen hammer to set those rivets in non critical areas, using the ball end to round off the rivet and make a ball at the rear. Even made rivets out of thick copper wire as well using that method.