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Graphite whiskers have been grown in a dc arc under a pressure of 92 atmospheres of argon and at 3900°K. They are embedded in a solid matrix of graphite which builds up by diffusion of carbon vapor from the positive to the negative electrode. Diameters range from a fraction of a micron to over five microns, with recoverable lengths up to 3 cm. They consist of one or more concentric tubes, each tube being in the form of a scroll, or rolled-up sheet of graphite layers, extending continuously along the length of the whisker, with the c axis exactly perpendicular to the whisker axis. They exhibit a high degree of flexibility, tensile strengths up to 2000 kg-mm−2, Young's modulus in excess of 7×1012 dyne-cm−2, and values of room-temperature resistivity of around 65 μohm-cm, which approximates the single crystal value.

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Articles you may be interested inAn enhanced continuum modeling of the ideal strength and the angle of twist in tensile behavior of singlewalled carbon nanotubes A modified Weibull model for tensile strength distribution of carbon nanotube fibers with strain rate and size effectsThe strength of anisotropic polycrystalJine carbon fibers was investigated. Theoretical estimates of the strength of graphite are far higher than observed values for carbonized rayon fibers, and we have searched for an explanation. Internal "grain boundaries" in the fibers can account for the reduced strength inasmuch as the fracture appears to be intergranular. The "grains" are believed to be axially oriented fibrils, apapproximately 500-A across. Experimental evidence for some inelastic behavior in carbon fibers at room temperature was obtained from bending experiments on single filaments. The results were interpreted in terms of local "yielding" or rupture of cross-link bonds between adjacent fibrils. The stress at which such "yielding" takes place in bending is approximately equal to the failure stress in a tensile test. Although a Griffith model of completely brittle fracture in tensile tests was considered, the possibility that local "yielding" might precede tensile fracture seemed more likely. Consideration of the brittle failure model and the localized plastic flow model both lead to the same conclusion: The tensile strength of carbonized rayon fibers is limited by the fibrillar microstructure and cannot be expected to approach the theoretical estimates for graphite single crystals.

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