Re: Carbon-carbon is...?
From: Peter Fairbrother (zenadsl6186_at_zen.co.uk)
Date: 12/28/04
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- In reply to: Len Lekx: "Carbon-carbon is...?"
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To: sci-space-tech@moderators.isc.org Date: Tue, 28 Dec 2004 19:23:07 +0000
Len Lekx wrote:
> Just out of curiosity...
>
> What is the carbon-carbon heat shielding on the leading edges and
> nose of the Shuttle composed of? I'm assuming that part of it is a
> grahpite-fiber cloth material, but is it embedded in a ceramic
> material, or a high-temperature epoxy?
It's carbon fibres embedded in amorphous[1] carbon.
RCC (reinforced carbon-carbon) starts as carbon fibre cloth in phenolic
resin, shaped and cured. This is then pyrolysed (heated white-hot in the
absence of air), which decomposes the resin leaving some of the carbon from
the resin behind in a sort of foamy carbon structure, with the unaffected
carbon fibres still running through it.
This is vaccuum-impregnated with furfuryl alcohol[2] and pyrolysed again,
which leaves a bit more carbon behind. The impregnation and pyrolysis is
repeated, usually twice more, until the final material has only few and
small holes in it.
RCC is light, strong, and will take huge temperatures, and take huge
temperature shocks - but it is still almost pure carbon, and will burn in
the air. For shuttle use it is coated in silicon carbide and silica to
prevent burning.
For use as the chambers of small to medium rocket motors it is sometimes
coated with rhenium and/or iridium.
RCC is said to be beyond home workshop construction, but I don't really see
why, if you can get the required high temeratures. You might just be able to
make it in a suitable microwave oven based furnace.
Which reminds me, I must go down the sales and get some more microwave
ovens; though Tesco and Asda both do cheap ones for £25 now, so maybe I
won't bother.
[1] amorphous, "without shape", here meaning that the carbon does not have a
well-defined crystal structure, unlike eg diamond or graphite.
[2] aka furfural alcohol - or perhaps with furfuryl furfurate, depending on
who you read, which is a similarish but non-identical chemical, an ester of
furfuryl alcohol and pyromucic (aka furoic) acid. I've never made RCC, maybe
one is better, but I'd guess either would do about the same job.
[3] names of chemicals are difficult. Where they exist I usually use common
UK names and give common US names, eg furfuryl alcohol is a UK common name
and furfural alcohol is a US common name; otherwise I use IUPAC names, which
chemists use (I am a chemist); or ISO names (which are supposedly the
"official" names, but there aren't enough of them, and hardly anyone uses
them).
Of course sometimes all these names will be the same - only I can't think of
an example.
-- Peter Fairbrother
- Previous message: John Perry: "Re: Carbon-carbon is...?"
- In reply to: Len Lekx: "Carbon-carbon is...?"
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