I came across a pile of old toasters (well, about 5) last year, and recycled them into good bits and junk. The mica sheets in there are perfect for thermally-conductive, insulating material. Why even to buy a new one at WalMart for $7 gives a lot of mica. With only 12 volts, the mica can be very thin, and with a bit of practice with a razor blade, it can be cleaved into very thin sheets.
The holiday stuff is gone, but they have rolls of 1 mil X 30" X 144" (0.0254mm X 76cm X 3.6m) polypropylene to gift wrap baskets, $1.97 + tax. This might work fairly well. Here's some properties from various sites:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Electrical Properties
Dielectric constant @1MHz : 2.2-2.6 Dissipation factor @1MHz : 0.0003 - 0.0005 Surface resistivity : 10^13 Ohm/sq Volume resistivity : 10^16-10^18 Ohm/cm
Thermal Properties
Coefficient of thermal expansion : 100-180 (x10-6 K-1) Heat-deflection temperature - 0.45MPa : 100-105C Heat-deflection temperature - 1.8MPa : 60-65C Lower working temperature : -10 to -60C Specific heat : 1700 - 1900 (J K-1 kg-1) Thermal conductivity @23C : 0.1-0.22 W/m-1 K-1 Upper working temperature : 90-120C
Properties for Polypropylene Film
Dielectric Strength @25um thick : 200 kV/mm (5 kV/mil) Elongation at Break % : 50-1000 Heat-sealing Temperature : 140-205C Initial Tear Strength : 18-27 g um-1
Melting point Tm : 160-168C Vicat softening point Tv : 146-150C Heat deflection temperature THDT : 50-60C max. continuous service temperature air Tml : 90-120C
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Not too bad. 5kV breakdown, usable to 100C. The 1 mil thickness helps to lower the thermal resistance. I'll give it a try and see what happens.
Regards,
Mike Monett
Antiviral, Antibacterial Silver Solution:
The value for mylar can't be right!
And this is nonsense:
"For many applications a base that was made only of copper would probably be too effective at transferring heat. Heat applied to a small region would be transferred so rapidly that it wouldn't have time to diffuse across the pot's bottom. This would result in uneven cooking and possibly even local areas of scorching. Capping the base with stainless steel slows the immediate rate of heat transfer from the burner or heating element, but once this heat enters the copper core its high conductivity would spread the heat rapidly and evenly to all parts of the base."
If it's not an insulator, using it has to hurt, no matter how high the thermal conductivity. If it inhibits lateral heat spreading, as the graphite will, it could make things a lot worse.
At low frequencies, yes. But 1 LPM of water flow has an effective theta of about 0.014 K/W. You can run 1 LPM through some long, skinny plastic tubes and have a tiny effective capacitance (and kilovolts of isolation, if you keep the water clean.)
Machining is probably good enough. The baseplate of a power transistor is, what, 50 mils thick maybe, so if you machine the heatsink to 50 uinch flatness, that's 1000:1.
Hard anodize is pretty good, up to a couple of hundred volts maybe. We really need a mil of diamond. It's sad that nature is so stingy with diamonds.
John
It might make a good spacer. I just measured 2.5 mils. It's reasonably consistent over a few sheets.
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So get man-made ones...
Post-Its seem to be consistantly 4 mils. Soaked in baby oil, they'd be about as good as an 8-mil sil-pad.
John
Agreed
The mica can be shaved into very thin slices. Not that much of the stuff going around these days though . . . Great for insulators not available, like that DS501 you're dying to make a class A amp out of.
And toasters? I wouldn't trade my antique 1940 for anything. burns the bread perfectly.
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John, you have soul.
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On Thu, 28 Dec 2006 09:40:22 -0600, John Gave us:
You forgot to mention USED media. One needs the cream impregnated toilet paper.
On Thu, 28 Dec 2006 09:48:04 -0800, John Fields Gave us:
And I had such hopes.
On 28 Dec 2006 12:36:13 -0800, snipped-for-privacy@yahoo.com Gave us:
Carbon nanotubes are being considered for that very purpose.
On Fri, 29 Dec 2006 10:08:43 +1300, Barry Lennox Gave us:
Excellent answer to the thread topic!
On Thu, 28 Dec 2006 14:03:43 -0800, John Larkin Gave us:
We ran unpotted 50kV supplies in fluorinert. It is a dielectric fluid with 1.5 kV per mil isolation capacity.
I have, however, seen said 50kV supply arc up out of the fluorinert toward a pointed spike at ground potential that was brought in slowly from 4 feet away. Gradients are cool.
I'm a high school gradient. :-]
I'm a college gradient too! :-]
For the industry, yes. But for the physics here and the science. Wonder is all we have till we do.
I like NASA Tech Briefs. Hehehehe ;-]
I've seen them at 100 mils, and more as well. They are typically die cut from copper flat stock either before or after plating as well.
They don't do anything to them. They take on the flatness of the die base they get punched in, and add the granularity of the plating. It's a nice, fuzzy surface that gives one that warm, fuzzy feeling. ;-]
I have seen much better stats than that an mil spec for hard anodize has a table of four levels IIRC. They correspond with anodization depth, and carry other attribute changes as well, like higher withstand voltage.
I like crystals. I have a laser disc from the smithsonian on gems and minerals that is sooo cool! Likely out there on DVD by now, though i never looked. That was over a decade ago.
On Thu, 28 Dec 2006 16:58:16 -0600, snipped-for-privacy@ip-64-139-1-69.sjc.megapath.net (Hal Murray) Gave us:
Under the compression of attachment, I am sure it would come in a bit thinner. Try tightening your micrometer a bit against it.
On Thu, 28 Dec 2006 20:22:49 -0500, default Gave us:
It's expensive. It has to be mined from the earth.
Indeed. It's highlighted in cyan, suggesting it's a place-filler only. I'm afraid I didn't scrutinize the source, just glanced and saw a complete-looking table of conductances.
Could be true for cookware using a thin layer of copper: vertical transport would be quick, lateral transport poor.
Point taken.
Machining the heatsink's finish to being a whole bunch better than the semiconductor's package clearly doesn't do much--microscopically the device will still rest mostly on the peaks of the rougher surface. Ultra-finishing both, though, might produce more intimate metal-to-metal contact.
Hard anodize is quite good I understand, but porous. About half being open space, I wondered recently if a denser, non-porous coating such as might be twice as thermally conductive. Hence the passing interest in microplasmic coatings. But I'm just blowin' smoke here--I've got no need for such presently.
Darn right -- not only a _girl's_ best friend, I'd like a few for just about everything--heat sinking, machining, optics...
Best, James Arthur
I was about to suggest cigarette papers impregnated with paraffin wax.
-- Bye. Jasen
-- Sad. First stem cells, now baby oil...
You probably want the extra-virgin stuff from the first squeezing.
Best regards, Spehro Pefhany
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In the old days I used to anodise the aluminium to insulate TO3 devices. Could get close to 500volts breakdown, depending on how long you cooked. A spot of ink would give you some colour as well.
--
Best Regards:
Baron.
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