The Army Space and Missile Defense Command, Huntsville, Ala., recently recruited Touchstone Research Laboratory Ltd., Triadelphia, W.V., to continue development of its carbon-foam technology.
The coal-based carbon-foam material, called CFOAM, is a next-generation structural material that's lightweight, fire resistant, impact absorbing, and can be thermally insulating or conducting. The material's electrical conductivity can also be varied over nine orders of magnitude (0.01 to 106Ω) This makes it a perfect electrical conductor (PEC) of wide-band frequency and wide-angle incidence for radar-absorbing and electromagnetic shielding applications. The foams bond easily to metal and other dissimilar materials and their mechanical properties won't degrade with high temperature if protected from oxidation.
CFOAM is a cellular foam with densities as high as 1.4 gm/cm3 and as low as 0.1 gm/cm3, in the lab. Current development activities are looking at producing substrates with even lower densities. The carbon foam comes in a variety of near-netshape configurations or it can be easily cut, milled, and turned with conventional machine tools. The Touchstone carbonfoammaking process can vary cell size and degree of openness to support compressive strengths over 10 kpsi. Development goals are to push these limits to strengths of 15 kpsi.
The material also has a low coefficient of thermal expansion (CTE). This, coupled with its inherent stiffness, makes it an option for lightweight mirrors used in space telescopes and high power lasers. It easily shapes to the desired optical surface, readily accepts a variety of surface coatings, and will distort little under temperature extremes in space.
The material's high strength coupled with low weight and resistance to fire and impacts makes it an alternative for aircraft and ship applications. This includes interior panels and nonstructural bulkheads, structural insulation or sound absorption panels, and radar or electromagnetic shielding/absorption panels for ship topside structures. CFOAM can replace existing core materials where stringent fire, smoke, and toxicity regulations exceed what's possible with polymer foams, honeycombs (polymer, paper, or metal), or balsa wood.
In addition, makers of protonexchange-membrane (PEM) fuel cells are also looking at carbon foams to replace the cell's current bipolar plates. CFOAM is an economical alternative that stands up to fuel cell environments (i.e., under acidic, oxidizing, and reducing conditions).
Jean M. Hoffman
Touchstone Research Laboratory Ltd.,
(304) 547-5800, www.trl.com