Research and Development Company

    Approximately 75% of the activities at ASI are related to carbon nanofibers and composites in one form or another. For example, ASI has performed pioneering work in the development of vapor grown carbon nanofiber, and composites thereof, including polymer matrix, graphite/epoxy, carbon/carbon, and metal matrix composites. ASI fabricates carbon nanofibers using technology jointly developed between ASI and General Motors (specifically, General Motors Research and Delphi Chassis) under a licensing agreement. Essentially, these carbon nanofibers are related to the so-called Fullerene or C60 "buckyball" molecule led to the 1996 Nobel Prize in Chemistry for Robert F. Curl, Harold W. Kroto and Richard E. Smalley. Three different variations of nanofibers are of interest for producing electrically and thermally enhanced adhesives. 

• Pyrograf^®-I is a substrate grown fiber which attains lengths of up to 10 cm.  Pyrograf-I has a larger diameter than Pyrograf-III and performs high thermal conductivity.  It is useful in carbon pre-form or metal matrix composites for thermal management applications.

• Pyrograf^®-III is grown completely in the gas phase, and tends to be grown in an entangled mass. It is now grown without any detectable pyrolytic overcoat. Pyrograf^®-III may be properly referred to as a nanofiber. Pyrograf^®-III is highly ordered without heat treatment (although heat treatment is still useful as a means of removing impurities, if desired).

 
• Pyrograf^®-IV is similar to Pyrograf^®-III, but contains an additional pyrolytic overcoat so that it attains a diameter of a few microns. Therefore, it is not properly referred to as a "nanofiber" but actually becomes a "microfiber." Because of its larger diameter, Pyrograf^®-IV can be considered as an additive for high thermal conductivity.


    The properties of the three Pyrograf^® types are summarized below (incidentally, ASI does not offer a material called Pyrograf^®-II. It was abandoned in favor of Pyrograf^®-III by the mid 1990s). It is not practical to measure single-fiber properties for very tiny fibers, but the strength, modulus, and CTE are inferred to be similar for all three materials (as measured for the case of Pyrograf^®-I). 

Properties of PYROGRAF® Materials Property Pyrograf®-I (PR-I-HT) Pyrograf®-III (PR-24-PS) Pyrograf®-IV Description macroscopic fiber nanofiber microfiber Ultimate Strength, GPa 7.0 7.0 7.0 Tensile Modulus, GPa 600 600 600 Diameter, microns 10 0.060 - 0.2 2,000 Length, microns 1 to 10 cm 100 100 Density, g/cm3 2.1 1.8 1.9 Pyrolytic layer thickness, nanometers ~500 ~20 none CTE, ppm * -1.0 -1.0 -1.0 Electrical Resistivity, micro-ohm-cm 55 55 55 Thermal Conductivity, W/K-m 1950 TBD TBD

*  Note that the coefficient of thermal expansion of these materials is slightly negative, in contrast to the polymer matrix, which usually expands significantly upon heating. Thermal expansion coefficient of polymer nanocomposites can be significantly reduced. Thus thermal strain is likely to be much lower in a polymer nanocomposite, which can be an important advantage for such materials.

ASI has an extensive data base on these carbon materials including different catalysts, substrates, and gas flow configurations for Pyrograf® fiber production; oxidation properties of carbon materials as a function of temperature; processing conditions for carbon nanomaterials for use in metal matrix, carbon matrix, and polymer matrix composites; measuring requisite properties of density, thermal conductivity, thermal expansion, and electrical conductivity.

    ASI has hot filament assisted CVD and microwave plasma assisted CVD Diamond reactors. Currently, diamond films, up to two inches in diameter, can be deposited on Si, Mo, and carbon/carbon composite substrates. Additionally, ASI can also coat tungsten wire and carbon fiber with diamond thin films.