Characterization of Structure and Microtexture of Carbon Materials by Magnetoresistance Technique

Abstract

Various carbon materials have been classified in two categories such as graphitizable and nongraphitizable carbons, or soft and hard carbons. For the characterization of the textures of the various carbon materials, high-resolution transmission electron microscopy, particularly dark-field technique, is efficient. Some disorganized carbon materials, such as turbostratic carbons, are known to give negative values of magnetoresistance. Since negative magnetoresistance is very characteristic for such carbon materials, much experimental work has been done. The magnetoresistance anisotropy on a specimen gives an information regarding the preferred orientation of the carbon layers along the main current direction in the specimen and in the plane perpendicular to this direction. Highly oriented graphites here mean graphite crystals with almost complete parallel alignment of graphite basal planes. The study for PAN/GC was first carried out by Hishiyama et al. by scanning electron microscopy, polarized light microscopy, and measurements of density, X-ray diffraction, and magnetoresistance.