🚀 go-pugleaf

-From: gary@ke4zv.uucp (Gary Coffman)
-Subject: Re: Let's be more specific (was: Stupid Shut Cost arguements)
-Date: 11 Jan 93 15:48:12 GMT

-Shuttle designers... chose to use refractory silicates in the form of
-tiles. These are very poor conductors of heat, you can place your bare
-hand against one side of the tile while playing an oxy-acetylene torch
-on the other and not notice a temperature rise. 

I think perhaps you mean a propane torch, or butane torch like Mary described.
Pulling some numbers from the Rogers report and elsewhere, the leading
edges of the Shuttle wings have to withstand heating up to 2750 F, and are
made of layers of graphite cloth in a carbon matrix, with the outer layers
chemically converted to silicon carbide. The upper fuselage, the coolest
portion during reentry, is only heated to about 600 F. The Shuttle has 
high-temperature and low-temperature ceramic tiles, which are described in
this report as being "nearly pure glass" (I had thought they were silica),
with nearly 90% of the volume being "air". The low-temperature ceramic tiles
are are rated to 1200 F, and the high-temperature tiles to a higher value,
but something below wing leading-edge temperatures.

While such temperature resistance is admirable, a properly-designed
acetylene torch can heat a thermally isolated object to 6000 F (~ 3300 C).
I wouldn't expect any trouble melting most ceramics - I've accidentally
melted fire bricks that I was using as a backstop for acetylene welding.

>From the 1961 CRC handbook, here are some temperature ratings for ceramics
and other materials:

  SAFE CONTINUOUS OPERATING TEMPERATURE / MELTING POINT
     Material          C         F      /    C        F
     --------        ----      ----        ----     ----
     Porcelain       1195      2185     /  ....     ....
     Alumina (84%)   1400      2550     /  ....     ....
     Zircon          1455      2650     /  2500     4530
     Silicon carbide 1510      2750     /  2295     4160 (volatilizes)
     Silica          1620      2950     /  1670     3038
     Alumina (96%)   1700      3100     /  ....     ....
     Alumina (100%)  1950      3540     /  2050     3720
     Zirconia        2316      4200     /  2680     4850
     Magnesia        ....      ....     /  2800     5072
     Titanium boride ....      ....     /  2900     5250
     Thoria           ...      ....     /  3110     5630
     Titanium carbide ...      ....     /  3125     5660
     Tantalum nitride ...      ....     /  3440     6050
     Tungsten         ...      ....     /  3370     6100
     Zirconium carbide ..      ....     /  3520     6370
     Graphite         ...      ....     /  3800     6870
     Tantalum carbide ...      ....     /  3850     7025
     Hafnium carbide  ...      ....     /  4160     7520

John Roberts
roberts@cmr.ncsl.nist.gov