"Pyrolytic Graphite"

[John Larkin]

On Tue, 18 Aug 2015 14:18:31 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 08/18/2015 10:55 AM, John Devereux wrote:

"2-5 times higher thermal conductivity than copper"

I have not heard much about this wonder material, is it actually any use
for anything?



It's diamagnetic enough that you can levitate it over a quadrupole made
of permanent magnets. The more physics somebody knows, the bigger the
double-take they do when you show them.

Cheers

Phil Hobbs

People shout "Earnshaw's theorem!" to prove that levitation is
impossible, but Earnshaw didn't allow for magnetic repulsion.

High temp superconductors above a magnet are interesting.

http://i.ytimg.com/vi/nWTSzBWEsms/hqdefault.jpg

https://upload.wikimedia.org/wikipedia/commons/9/99/Stable_Levitation_of_a_magnet_on_a_superconductor.jpg

but why doesn't it slide off to the side?

 

[Phil Hobbs]

On 8/20/2015 8:35 PM, John Larkin wrote:

On Tue, 18 Aug 2015 14:18:31 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 08/18/2015 10:55 AM, John Devereux wrote:

"2-5 times higher thermal conductivity than copper"

I have not heard much about this wonder material, is it actually any use
for anything?



It's diamagnetic enough that you can levitate it over a quadrupole made
of permanent magnets. The more physics somebody knows, the bigger the
double-take they do when you show them.

Cheers

Phil Hobbs

People shout "Earnshaw's theorem!" to prove that levitation is
impossible, but Earnshaw didn't allow for magnetic repulsion.

High temp superconductors above a magnet are interesting.

http://i.ytimg.com/vi/nWTSzBWEsms/hqdefault.jpg

https://upload.wikimedia.org/wikipedia/commons/9/99/Stable_Levitation_of_a_magnet_on_a_superconductor.jpg

but why doesn't it slide off to the side?

I posted pictures and a cellphone movie of the diamagnetic maglev thing
some years back. (It's still sitting above one of my lab benches.)

It does want to slide off the edge if you use one magnet, but four of
them arranged as a quadrupole make a nice potential minimum for the
graphite sheet to sit in. If you make the sheet too big, it slides off
the side anyway.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[whit3rd]

On Thursday, August 20, 2015 at 5:29:39 PM UTC-7, John Larkin wrote:

> Do you use this stuff? Got any pix?

I've seen it in use, just as a drab little cap on a chip; it
covered a flatpack chip, served only to spread the heat
over the area of the chip (evening out any hot spots).

There's plenty of pix on the web; this site shows the lateral heat spreading
pretty well

<http://www.elecdiv.kaneka.co.jp/english/graphite/techno01.html>

 

[Bill Beaty]

On Tuesday, August 18, 2015 at 7:55:34 AM UTC-7, John Devereux wrote:

I have not heard much about this wonder material, is it actually any use
for anything?

Buy it at digikey. Use it on processor heat sinks instead of silicone thermal grease.

If you pry off a CPU, and the heatsink is covered with silver-black flakey stuff, that's pyrolytic graphics thermal conductor.

Also used in maglev toys, since pyro graphite will levitate a few mm in high-gradient fields. A little "raft" of many neo-magnet cubes, arranged in a checkerboard, can lift a thin "puck" made of pyrolytic graphite. Play air-hockey without needing air.

Scitoys website was selling hunks years ago, they may be still.

 

[Bill Sloman]

On Friday, 21 August 2015 20:30:16 UTC+10, piglet wrote:

On 20/08/2015 05:09, Kevin McMurtrie wrote:
It conducts better than you'd think and it can conform to uneven
surfaces better than copper.


I think its cousin graphene is seeing early commercial use in LED lamps
to conduct heat from the LED die to the heatsinks.

Graphene is a single layer of carbon atoms. It's a little tricky to use it for heat-sinking.

We used woven carbon cloth to thermally couple a Peltier junction to an aluminium heat sink back in 1993 - it worked fine then and it's still commercially available, and my guess would be that more likely to be used to heatsink an LED die.

--
Bill Sloman, Sydney

 

On Friday, 21 August 2015 01:35:29 UTC+1, John Larkin wrote:

High temp superconductors above a magnet are interesting.
....
but why doesn't it slide off to the side?

Flux pinning by dislocations is what I was taught a long time ago.
The explanation might of course have changed by now.

John

 

[piglet]

On 20/08/2015 05:09, Kevin McMurtrie wrote:

It conducts better than you'd think and it can conform to uneven
surfaces better than copper.

I think its cousin graphene is seeing early commercial use in LED lamps
to conduct heat from the LED die to the heatsinks.

piglet

 

[piglet]

On 21/08/2015 12:41, Bill Sloman wrote:

On Friday, 21 August 2015 20:30:16 UTC+10, piglet wrote:
On 20/08/2015 05:09, Kevin McMurtrie wrote:
It conducts better than you'd think and it can conform to uneven
surfaces better than copper.


I think its cousin graphene is seeing early commercial use in LED lamps
to conduct heat from the LED die to the heatsinks.

Graphene is a single layer of carbon atoms. It's a little tricky to use it for heat-sinking.

We used woven carbon cloth to thermally couple a Peltier junction to an aluminium heat sink back in 1993 - it worked fine then and it's still commercially available, and my guess would be that more likely to be used to heatsink an LED die.

Yes, I was referring to that news story that made such a furore a few
months back about a graphene light bulb. Turns out the graphene helps
cool the leds.

piglet

 

[Phil Hobbs]

On 8/21/2015 8:30 AM, jrwalliker@gmail.com wrote:

On Friday, 21 August 2015 01:35:29 UTC+1, John Larkin wrote:

High temp superconductors above a magnet are interesting.
...
but why doesn't it slide off to the side?

Flux pinning by dislocations is what I was taught a long time ago.
The explanation might of course have changed by now.

John

IIRC high-TC superconductors are Type 2, so they contain flux vortices
that don't move easily.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[Syd Rumpo]

On 21/08/2015 14:13, piglet wrote:

On 21/08/2015 12:41, Bill Sloman wrote:
On Friday, 21 August 2015 20:30:16 UTC+10, piglet wrote:
On 20/08/2015 05:09, Kevin McMurtrie wrote:
It conducts better than you'd think and it can conform to uneven
surfaces better than copper.


I think its cousin graphene is seeing early commercial use in LED lamps
to conduct heat from the LED die to the heatsinks.

Graphene is a single layer of carbon atoms. It's a little tricky to
use it for heat-sinking.

We used woven carbon cloth to thermally couple a Peltier junction to
an aluminium heat sink back in 1993 - it worked fine then and it's
still commercially available, and my guess would be that more likely
to be used to heatsink an LED die.


Yes, I was referring to that news story that made such a furore a few
months back about a graphene light bulb. Turns out the graphene helps
cool the leds.

piglet

.... helps *sell* the LEDs, Shirley?

Cheers
--
Syd

 

[Kevin McMurtrie]

In article <t7ubtapm52ods691ervsqv4n5cg03errh8@4ax.com>,
John Larkin <jlarkin@highlandtechnology.com> wrote:

On Wed, 19 Aug 2015 21:09:30 -0700, Kevin McMurtrie
mcmurtrie@pixelmemory.us> wrote:

In article <1749ta5a81f0r4vaglas487iiijvk3lahc@4ax.com>,
John Larkin <jlarkin@highlandtechnology.com> wrote:

On Tue, 18 Aug 2015 22:46:07 -0700 (PDT), edward.ming.lee@gmail.com
wrote:

On Tuesday, August 18, 2015 at 9:06:26 PM UTC-7, John Larkin wrote:
On Tue, 18 Aug 2015 20:02:02 -0700, Robert Baer
robertbaer@localnet.com> wrote:

John Larkin wrote:
On Tue, 18 Aug 2015 15:55:30 +0100, John Devereux
john@devereux.me.uk> wrote:


"2-5 times higher thermal conductivity than copper"

It's very anisotropic, with high thermal conductivity only in the
plane of a sheet. That makes it useless for most electronic
applications.

* Don't you have_any_ imagination?

Not enough to do dumb things.


Use that property to carry heat AWAY from a pesky source..(not too
hard to solve thermal coupling on both ends).

Check out the pricing for small, thin pieces of the stuff:

http://www.digikey.com/product-search/en?keywords=Pyrolytic

That would be insane as a heat spreader. Aluminum or copper make way
more sense.

Actually, the 90x60 is reasonably priced at $3.29.

Nice for floating above magnets, but it's as thick as a sheet of
paper, not much use as a heat spreader.

It conducts better than you'd think and it can conform to uneven
surfaces better than copper.

You've still got to do the numbers. If the p.g. conducts heat 5x
better than aluminum, but the aluminum is 20x thicker, the cheap
aluminum wins.

"Conforming" is a mixed blessing. To conduct heat, you need an
intimate contact with the thing to be cooled and with the place to
dump the heat. That implies adhesives or something to get the flexy
p.g. to stick to a chip or whatever, and an adhesive will wreck the
thermal conductivity.

There are no slabs of copper or aluminum in handheld electronics. Like
I said, it's good for very small devices and SMDs. Ask Apple if they're
rather make an iPhone 30% heavier with copper, 30% thicker with
aluminum, or spend $5 on a pyrolytic graphite sticker.

--
I will not see posts from astraweb, theremailer, dizum, or google
because they host Usenet flooders.

 

[John Larkin]

On Fri, 21 Aug 2015 01:07:50 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

On Thursday, August 20, 2015 at 5:29:39 PM UTC-7, John Larkin wrote:

Do you use this stuff? Got any pix?

I've seen it in use, just as a drab little cap on a chip; it
covered a flatpack chip, served only to spread the heat
over the area of the chip (evening out any hot spots).

Lateral heat spreading can help a lot, distribute the central hot-spot
above the silicon. But aluminum or copper work too.

I guess you can cut the carbon stuff with scissors or a paper cutter
if you don't want to work metal. So somebody should sell it in pre-cut
pieces for sticking onto chips.

There's plenty of pix on the web; this site shows the lateral heat spreading
pretty well

http://www.elecdiv.kaneka.co.jp/english/graphite/techno01.html

Sure, but there's no reason to use 25u thick copper or aluminum.


--

John Larkin Highland Technology, Inc
lunatic fringe electronics

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com