Carbon Foam Military Applications
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The document discusses carbon foam (cfoam), a lightweight and versatile structural material with benefits such as fire resistance and impact absorption, making it suitable for aerospace and military applications. Developed from coal tar and petroleum pitches, cfoam exhibits excellent thermal and electrical properties, and can replace traditional materials in radar-absorbing systems, fuel cells, and various structural components. Current research is focused on optimizing its properties for specific applications, enhancing its use in next-generation technology.
Carbon Foam Military Applications
- 1. CARBON FOAM Visit www.seminarlinks.blogspot.com to Download
- 2. INTRODUCTION • 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. • Light weight CFoam is a sponge-like, rigid and high performance engineering material in which carbon ligaments are interconnected to each other. • In early days CFoam is prepared from thermosetting polymeric material by heat treatment under controlled atmosphere. • Later on, coal tar and petroleum pitches are used for CFoam synthesis.
- 3. • In the modern technological world, scientists are constantly in the search of new materials to replace existing high density radar absorbing materials (RAM) for civil and military aerospace applications. • In these applications it is usually important for aircraft and ships to suppress microwave reflection so as to improve their combat survivability. • The absorption of the electromagnetic energy in medium between the radar and a protected target by use of RAM is one approach to reduce the radar signatures of targets. • RAM is classified into two categories as magnetic and dielectric absorbing materials.
- 4. • The magnetic absorbers depend on the magnetic hysteresis effect, which is attained in magnetic materials such as ferrites. • But densities of the magnetic materials are generally high and absorbing bandwidths for magnetic absorbers are usually narrow. • On the other hand, dielectric materials are light weight • But do not match up to the absorptivity of magnetic absorbers. • These two types of materials have different advantages and disadvantages when they are applied as absorbers. • They can be used together as a composite, and the magnetic material is usually the base one, but high density of the material is still of great concern. • Therefore, in order to meet desired requirements, many materials have been singled out or synthesized, among them carbon materials have been considered as the most promising candidates since World War I.
- 5. Among the different carbon materials, light weight carbon foam (CFoam) has emerged as a promising candidate for EMI shielding owing to its outstanding properties such as low density, large surface area with open cell wall structure, good thermal/electrical transport properties and mechanical stability. Visit www.seminarlinks.blogspot.com to Download
- 6. STRUCTURE • Carbon foams are rigid, porous materials consisting of an interconnected network of ligaments. • They can have open cell structure where pores are interconnected to one another or closed cell structure where pores are isolated from one another. • Partially graphitic carbon foams (Fig1) were prepared from coal-based carbon precursor. Fig1: SEM images of carbon foam derived from raw coal (a), coal solvent-extracts
- 7. The carbon foam with graphitic structure (fig2) was synthesized by pitch based carbon (natural or synthesized pitch). Fig2: SEM images of carbon foam derived from (c), petroleum pitch (d), QI-free coal tar pitch
- 8. • Precursor used to synthesize carbon foams with amorphous structure is mainly thermosetting resins like polyurethane, phenolic, furfuryl , polyimides, etc. • Non-graphitizable or glassy carbon foams are shown in figure3. Fig3: Glassy carbon foam (e) and (f) phenolic based carbon foam
- 9. Process for synthesis of as such CFoam, Fe3O4 and Fe3O4-ZnO coated CFoam
- 10. Fig: SEM micrographs of CFoam (a) CFU, (b) CF-Fe3O4 and (c) CF-Fe3O4-ZnO
- 11. PROPERTIES • Properties of graphitic and non-graphitic carbon foam are listed in table on next slide. The most important properties are • High temperature resistance • Hardness • Low density • Low electrical resistance • Low friction • Low thermal resistance • Extreme resistance to chemical attack • Impermeability to gases and liquids. • Glassy carbon is widely used as an electrode material in electrochemistry, as well as for high temperature crucibles and as a component of some prosthetic devices.
- 12. ELECTRICAL CONDUCTIVITY • 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.
- 13. DENSITY • 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.
- 14. THERMAL CONDUCTIVITY • 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.
- 15. STRENGTH • 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.
- 16. FUEL CELL • 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).
- 17. CONCLUSION Carbon foams will help to enhance capabilities and improve affordability, supporting today’s warfighter. Applications for coal-based carbon foams continue to be developed as the material is accepted as a mainstream structural building block for tomorrow’s technology. Current application examples include targeted advances in composite tooling, vehicle blast mitigation, radar absorption, and ablation panels. Visit www.seminarlinks.blogspot.com to Download