Abstract:
ABLATIVES. Materials used for the outward dissipation of extremely high heats by mass removal. Their most common use is as an
external heat shield to protect supersonic aerospace vehicles from
an excessive buildup of heat caused by air friction at the surface. The
ablative material must have a low thermal conductivity in order that
the heat may remain concentrated in the thin surface layer. As the
surface of the ablator melts or sublimes, it is wiped away by the frictional forces that simultaneously heat newly exposed surfaces. The
heat is carried off with the material removed. The less material that
is lost, the more efficient is the ablative material. The ablative material also should have a high thermal capacity in the solid, liquid, and
gaseous states; a high heat of fusion and evaporation; and a high heat
of dissociation of its vapors. The ablative agent, or ablator, is usually
a carbonaceous organic compound, such as a phenolic plastic. As the
dissociation products are lost as liquid or vapor, the char is held in
place by the refractory reinforcing fibers, still giving a measure of
heat resistance. The effective life of an ablative is short, calculated in
seconds per millimeter of thicknes
