Abstract: A method for producing high strength, high modulus filament yarns of carbon fibers is provided by subjecting a mesophase-containing pitch to aging, separating (purifying) the resulting 100% mesophase and subjecting 100% mesophase to melt-spinning at 250.degree. to 350.degree. C. by using spinning nozzles having a greater cross-sectional area in the outlet part than the cross-sectional area in the narrowest inside the nozzles and further to thermosetting and carbonization whereby carbon fibers having a random (shape), turbulent flow shape or rather onion shape of carbon arrangement in cross-section are obtained.

Abstract: A method for producing a 100% mesophase pitch composed only of Q.I. and Q.S. components is provided. This method comprises subjecting petroleum-origin pitch to heat treatment with stirring under a stream of a hydrocarbon gas of small carbon atom numbers at atmospheric or superatmospheric pressure, holding said heat-treated pitch in quiescent state to melt and coalesce only the mesophase therein and dividing and separating non-mesophase and mesophase layers. Resulting 100% mesophase enables us to produce high strength, high modulus carbon fibers.

Abstract: A method for producing a 100% mesophase composed only of Q.I. component and Q.S. component is provided. This method comprises forming mesophase by the heat treatment of petroleum-origin pitch, subjecting the heat-formed pitch to a condition of heating under quiescent state to cause only the mesophase in the heat-formed pitch to grow and coalesce, separating only the non-mesophase of the upper layer and repeating the operation of the heat treatment and maintenance of heating under a quiescent state by the separated non-mesophase, as a raw material.

Abstract: A method for producing continuously 100% mesophase composed only of Q.I. component and Q.S. component in which a raw material of petroleum origin pitch is subjected continuously to a heat-treatment step in an amount necessary to produce a 100% mesophase taken out from a mesophase-growing and coalescing step, transferring the heat-formed pitch formed in the heat treatment step to a mesophase growing and coalescing step, taking out a definite amount of a non-mesophase pitch from the mesophase growing and coalescing step after stirring and heating treatment to return it to the heat-treatment step to repeat the stirring and heating treatment, and at the same time to take out 100% mesophase having constant properties from the mesophase growing and coalescing step.

Abstract: A method for producing a mesophase-containing pitch from petroleum pitch or coal tar pitch is disclosed. According to this method volatile distillate fractions, which are harmful to mesophase formation and present originally in the raw material pitch or formed as by-product during heat treatment time are driven off by using a carrier gas at a temperature of 360.degree. to 450.degree. C. in order to shorten the overall heat treatment time and advance the mesophase formation smoothly by the increase of stirring effect.