MEASUREMENTS AND CONTROL OF ANISOTROPY IN 10 COAL-BASED GRAPHITES

Using a solvent extraction process to produce high-purity extracts fro m untreated and hydrogenated coal, ten coal-based graphites with diffe rent levels of anisotropy have been produced. Anisotropy of these grap hites and that of H-451 (a petrocoke-based commercial graphite) has be en assessed by means of the intensity of the (002) line in X-ray diffr action (XRD), by magnetic susceptibility (chi), by the coefficient of thermal expansion (alpha), and by electrical conductivity (sigma) stud ies. Measurements were made along directions longitudinal (l) and tran sverse (t) to the extrusion direction. The XRD ratio R for the (002) l ine varies between 0.23 for the most anisotropic and 0.94 for the leas t anisotropic of the graphites. Chi(l)/chi(t) and alpha(l)/alpha(t) fo r various graphites increase systematically as R increases, although t he variations are not linear over the extended range. It is argued tha t measurements of R, chi(l)/chi(t), and alpha(l)/alpha(t) provide reli able techniques for the measurements of anisotropy in graphites. Exami nation of the relationship of the anisotropy to the nature of the prec ursors used in producing graphites shows that hydrogenation of coal pr ior to the extraction process produces anisotropic graphites, the anis otropy being controlled by the degree of hydrogenation. Furthermore, i t is shown that by blending appropriate amounts of hydrogenated and no nhydrogenated coal extracts, graphites of desired anisotropy can be pr oduced.