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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: silicone grease
Date: Mon, 1 Apr 2024 04:01:09 +1100
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On 1/04/2024 1:59 am, John Larkin wrote:
> On Sun, 31 Mar 2024 14:38:44 +0200, Robert Roland <fake@ddress.no>
> wrote:
> 
>> On Sat, 30 Mar 2024 11:14:10 -0700, John Larkin <jl@997PotHill.com>
>> wrote:
>>
>>> Give a nice flat mosfet package and a flat heat sink,
>>
>> There is no such thing as flat. There is only different levels of
>> rough. Extremely flat is extremely expensive.
>>
>> In theory, when you bolt two metal object together, they will only
>> contact at three microscopic points.
> 
> That "theory" assumes that both surfaces are infinitely rigid. The
> force on those three microscopic contact points would be enough to
> melt diamond.

Diamond doesn't melt at room temperature. There is a 
diamond/graphite/liquid carbon triple point at 12 GPa at 5000 K, but 
your lump of metal wouldn't get hot enough to get anywhere near that.

The three microscopic points will distort so that that the compressive 
force is spread over three finite - but small - areas.

With very clean surfaces under vacuum you get microwelding as the metal 
at the microscopic contact points diffuses into the surface it is 
squeezed up against. This can be a problem if you wan to dismantle your 
gear later.

<snip>

-- 
Bill Sloman, Sydney