Abstract: A graphitized fiber heat-treated at a temperature higher than 2300.degree. C. in an inert atmosphere, of which oxidation weight reduction rate A in dry air at 650.degree. C. is in the range defined by the equation (1), of which BET specific surface area S determine by nitrogen or krypton adsorption technique at -196.degree. C. is in the range defined by the equation (2), and of which pore volume determined by the carbon dioxide adsorption technique at 25.degree. C. is 0.001 ml/g or less: ##EQU1## where, A is the oxidation weight reduction rate in dry air at 650.degree. C. in min.sup.-1S is the specific surface area determine by nitrogen or kypton adsoprtion technique at -196.degree. C. in m.sup.2 g.sup.-1D is the mean monofilament diameter of the graphitized fiber in .mu.m and .rho. is the density of the graphitized fiber in gcm.sup.-3.

Abstract: In a method of producing mesophase pitch based carbon fibers, including the steps of melt-spinning a mesophase pitch through a nozzle (1) having at least one pair of a counter-bore (2) and a circular capillary (3) to form a pitch fiber and subjecting the pitch fiber to an infusible treatment, a carbonization treatment, and if necessary, a graphitization treatment, to form a carbon fiber, the nozzle has a degree of asymmetry .phi. of from 0.1 to 0.9, .phi. being defined by the following equation .phi.=S.sub.A /S.sub.B, wherein S.sub.A is an area of an inscribed circle in a contour of the cross-section of the counter-bore, which circles is perpendicular to the nozzle axis and has a center on the axis of the capillary and inscribed and S.sub.B is a total area of the cross-section of the counter-bore.

Abstract: A process for producing a carbon fiber by subjecting a pitch fiber, obtained by melt spinning a carbonaceous mesophase pitch, to stabilization, followed by a carbonization or graphitization treatment, wherein the stabilization is carried out under an oxidative atmosphere containing 0.1% to 40% by volume of NO.sub.2 and 4% to 40% by volume of H.sub.2 O at a temperature of from 100.degree. C. to 400.degree. C.

Abstract: A mesophase pitch suitable for carbon products, particularly for carbon fibers, which has a mesophase content of at least 40%, preferably at least 60%, and a larger mesophase domain, is produced by adding at least one part by weight of at least one of an alcohol and a phenol to 100 parts by weight of heavy bitumens, subjecting the resulting mixture to pretreatment by heating at least at 250.degree. C., and then subjecting the pretreated mixture to heat treatment until mesophases are formed.

Abstract: Separation and recovery of dibenzofuran of high purity is accomplished by distilling a coal tar fraction having boiling point range of 220.degree. to 300.degree. C. thereby producing a dibenzofuran fraction having a dibenzofuran content of not less than 30% by weight, a dibenzofuran/acenaphthene molar ratio of not less than 1.3, and a fluorene/dibenzofuran molar ratio of not more than 0.05, then introducing the dibenzofuran fraction obtained as described above into a continuous crystallization purification unit provided with a cooling zone for crystallization of the feed, a heating zone for melting the purified crystals, and a refining zone for enabling crystals being transferred from said cooling zone to said heating zone to come into counter current contact with a mass of molten crystals midway along the path between said two zones, and subjecting the dibenzofuran fraction to continuous crystallization purification therein.