From: Michael M. Butler (mmb@spies.com)
Date: Sun Jan 12 2003 - 05:15:33 MST
Eugen Leitl wrote about apples and oranges:
> On Thu, 9 Jan 2003, Michael M. Butler wrote:
>
>>The best temp performance polymers I know of are high-temp liquid crystals
>>used to mold, e.g., the connector housings for thermocouples. They spec out
>>at something well under 500F.
>
> Polymers are used in ablative heat shields in aerospace.
Yes, they are (see below) -- but they *ablate*.
> I see no reason
> why you can't have polymers performing adequately sustainably at 1000 K. I
> would count any molecular crystal as polymer, so diamond and graphite are
> polymers too....
You want to call a crystal a polymer? Go ahead. To me that's a bit like calling
cellulose an oligomer. Is anything that's not a liquid or a gas a polymer? If you squint.
Diamond is just cellulose that someone handed to Gaia and Superman.
I agree that the old convenient categories are blurring; Spectra fiber is a hydrocarbon
polymer with crystal-like properties because of relatively highly-aligned molecules
chemically the same as the stuff used for cheap squeeze bottles when it's amorphous.
The heat shields you mention (some have been made out of polyester-glass laminate;
are these what you're talking about? or if not, please be specific--some early ones
were made out of balsa wood) work well enough because the shock wave means the stuff
is in a relatively oxygen-starved environment, with radiative heating as the source
of the bulk of the energy to be dealt with, or so ISTR. And they do *ablate*, they
aren't passive. If you want to call a ceramic a polymer, we're back to Paragraph One.
The original question had to do with Santa Machining a Lamborghini engine.
Ablative materials are probably not the best choice for IC cylinder parts.
Or for close tolerance turbines. So that whole angle is a strawman in context,
I fear.
On to diamondoids and buckymaterials:
The original question was posed in the context of stuff that could be
laid down the way the stuff at MIT is being laid down. I don't see the
dots connecting next week for supermaterials or high-performance ceramics.
Santa-lathes and -potter's wheels are not out of the question, of course.
Slurries of nanocrystals were, however, mentioned in my reply, and I count both
diamonds and buckymaterials as being in the nanocrystalline camp at least as much
as in the polymer one. Ditto ceramics.
I agree that all this stuff is heading for the wall; some of it will stick.
MMB
I bet there are going to be a lot of buckymaterials that turn out to be pyrophoric.
That's OK, most of the fools out there accessorizing their cars with carbon fiber
'cause it looks baaad have no clue how it behaves in a crash, let alone a car fire.
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