Morphology and modulus of vapor grown carbon nano fibers
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Two types of morphologies have been observed in vapor grown carbon nano fibers (CNFs) using transmission electron microscopy (TEM). In one case, a truncated cone microstructure was observed, with outer and inner diameters of 60 and 25 nm, respectively. In this type of CNF, graphite sheets were oriented at about 15° to the fiber axis. The second type of fiber was a double-layer CNF with outer and inner diameters of 83 and 20 nm, respectively. A truncated cone structure was also observed in the double-layer CNF. Graphite sheets in the outer layer of the double-layer fibers were oriented along the nano fiber axis. Tensile modulus for the first type of nano fiber along its axis was calculated to be 50 GPa, and for the second type of fiber the calculated modulus value was in the 100–775 GPa range, depending on the outer layer orientation. Modulus calculations based on these two morphologies explain the wide ranging experimental CNF modulus values reported in the literature.
Partial support for this work from National Science Foundation, Air Force Office of Scientific Research (F49620-03-1-0124) and by the United States Air Force Research Laboratory at Wright-Patterson Air Force Base, OH (contract F33615-00-D-5006) is gratefully acknowledged.
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