Stealth foam and production method
Carbon foams exhibiting a dielectric constant of from about 2 to about 6 and simultaneously an electrical resistivity in the range of between about 1.E +00 ohm-cm and about 1.E +06 ohm-cm, demonstrate excellent radar emission absorptivity in the megahertz and gigahertz ranges.
1. A material comprising a carbon foam manufactured by a process comprising the steps of:
heating particulate coal in a pressurized non-oxidizing atmosphere having a pressure in the range of about 50 psi to about 500 psi, to a temperature in the range about 300° C. to about 600° to form a green foam; and
carbonizing said green foam to form a carbonized foam by heating said green foam to a maximum temperature ranging from about 600° C. to about 800° C., and soaking at this temperature for about 2 to about 30 minutes to produce a carbonized foam which exhibits a dielectric constant in the range of about 2 to about 6 and an electrical resistivity in the range of about 1.E +00 ohm-cm to about 1.E +06 ohm-cm.
2. The material of claim 1 , wherein said particulate coal exhibits a free swell index of between about 3.75 and about 4.5.
3. The material of claim 1 , wherein said particulate coal exhibits a free swell index in the range of about 3.5 to about 5.
4. The material of claim 1 , wherein said maximum temperature ranges from about 600° C. to about 700° C.
5. The material of claim 1 , wherein said soaking ranges from about 5 minutes to about 20 minutes.
6. The material of claim 1 , wherein said carbonized foam has a density ranging from about 0.1 g/cc to about 0.8 g/cc.
7. The material of claim 1 , wherein said carbonized foam has a density ranging from about 0.1 g/cc to about 0.6 g/cc.
8. A radar emissions absorbing body comprising:
a carbon foam on a surface of a body, wherein said carbon foam has the properties of a dielectric constant in the range of about 2 to about 6 and an electrical resistivity in the range of about 15 ohm-cm to about 1.E+ 06 ohm-cm.
9. The radar emissions absorbing body of claim 8 , wherein said carbon foam has a density ranging from about 0.1 g/cc to about 0.8 g/cc.
10. The radar emissions absorbing body of claim 8 , wherein said carbon foam has a density ranging from about 0.1 g/cc to about 0.6 g/cc.
11. A material comprising a carbon foam having a dielectric constant from about 2 to about 6 and an electrical resistivity from about 15 ohm-cm to about 1.E +06 ohm-cm.
12. The material of claim 11 , wherein said carbon foam is prepared from at least one selected from the group consisting of: particulate coal, coal tar pitch, petroleum pitch and carbonized polymeric materials.
13. The material of claim 11 , wherein said carbon foam is a coal-based carbon foam.
14. The material of claim 13 , wherein said carbon foam is derived from particulate coal exhibiting a free swell index from about 3.5 to about 5.0.
15. The material of claim 11 , wherein said coal-based carbon foam is a porous coal-based product having a density ranging from about 0.1 g/cm 3 to about 0.8 g/cm 3 .
16. The material of claim 11 , wherein said carbon foam has a density ranging from about 0.1 g/cc to about 0.6 g/cc.