Graphite Whiskers

A graphite whisker is a graphitic material formed by rolling a graphene sheet up into a scroll [23]. Except for the early work by Bacon [23], there is little literature about graphite whiskers. Graphite whiskers are formed in a dc discharge between carbon electrodes using 75-80 V and 70-76 A. In the arc apparatus, the diameter of the positive electrode is smaller than that of the negative electrode, and the discharge is carried out in an inert gas using a high gas pressure (92 atmospheres). As a result of this discharge, cylindrical boules with a hard shell were formed on the negative electrode. When these hard cylindrical boules were cracked open, scroll-like carbon whiskers up to ~3cm long and 1-5|j.m in diameter were found protruding from the fracture surfaces. The whiskers exhibited great crystalline perfection, high electrical conductivity, and high elastic modulus along the fiber axis. Since their discovery [23], graphite whiskers have provided the benchmark against which the performance of carbon fibers is measured. The growth of graphite whiskers by the arc method has many similarities to the growth of carbon nanotubes [24], especially MWNTs which do not require the use of a catalyst, except that graphite whiskers were grown at a higher gas pressure than is commonly used for nanotube growth. While MWNTs are generally found to be concentric cylinders of much smaller outer diameter, some reports have been given of scroll-like structures with outer diameters less than 100 nm [23].

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