From: zenadsl6186@zen.co.uk   
      
   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   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)