Pitch precursors affording excellent spinnability, high-level oxidation-resistance, and good carbonization yields were prepared by bromination–dehydrobromination of various ratios of pyrolyzed fuel oil and coal tar pitch. The pitches exhibited spinnabilities that were much better than those of pitches prepared via simple distillation. A pitch prepared using a 1:2 ratio of fuel oil and coal tar pitch exhibited the best tensile strength. Pitch fibers of diameter 8.9 ± 0.1 μm were stabilized at 270 °C without soaking time after heating at a rate of 0.5 °C/min and carbonized at 1100 °C for 1 h after heating at 5 °C/min. The resulting carbon fibers exhibited a tensile strength, elongation, Young’s modulus, and average diameter of 1700 ± 170 MPa, 1.6 ± 0.1%, 106 ± 37 GPa, and 7.1 ± 0.2 μm, respectively.

In this study, we tried to prepare an isotropic spinnable pitch which can be useful to prepare the general purpose carbon fiber through the co-carbonization of biomass tar with ethylene bottom oil under two different preparation methods (atmospheric distillation, pressurized distillation). The results showed that the ethylene bottom oil added co-carbonization was very effective to decrease of the oxygen contents for obtaining a stable spinnable pitch. The pressurized distillation was more effective to reduce the oxygen functional groups of pitches than atmospheric distillation. The obtained spinnable pitch by the pressurized distillation showed higher pitch yield of 42% and lower oxygen content of 9.12% than the spinnable pitch by the atmospheric distillation. The carbon fiber derived from the pressurized distillation spinnable pitch by carbonization at 800ºC for 5 min showed that the higher tensile strength of carbon fiber was increased up to 800 MPa.

Isotropic pitch-based fibers produced from coal tar pitch with the melt-blowing method were carbonized at temperatures ranging from 800 to 1600oC to investigate their crystalline structure and physical properties as a function of the carbonization temperature. The in-plane crystallite size (La) of the carbonized pitch fiber from X-ray diffraction increased monotonously by increasing the carbonization temperature resulting in a gradual increase in the electrical conductivity from 169 to 3800 S/cm. However, the variation in the d002 spacing and stacking height of the crystallite (Lc) showed that the structural order perpendicular to the graphene planes got worse in carbonization temperatures from 800 to 1200oC probably due to randomization through the process of gas evolution; however, structural ordering eventually occurred at around 1400oC. For the carbonized pitch powder without stabilization, structural ordering perpendicular to the graphene planes occurred at around 800–900oC indicating that oxygen was inserted during the stabilization process. Additionally, the shear stress that occurred during the melt-blowing process might interfere with the crystallization of the CPF.

In this work, thermal treatment accompanied with different acid treatments was applied to a commercial coal tar pitch (CTP) to obtain a spinnable precursor pitch for carbon fiber. In the case of thermal treatment only, a relatively high reaction temperature of between 380˚C and 400˚C was required to obtain a softening point (SP) range of 220˚C-260˚C and many meso-phase particles were created during the application of high reaction temperature. When nitric acid or sulfuric acid treatment was conducted before the thermal treatment, the precursor pitch with a proper SP range could be obtained at reaction temperatures of 280˚C-300˚C, which were about 100˚C lower than those for the case of thermal treatment only. With the acid treatments, the yield and SP of the precursor pitch increased dramatically and the formation of meso-phase was suppressed due to the lower reaction temperatures. Since the precursor pitches with acid and thermal treatment were not spinnable due to the inhomogeneity of properties such as molecular weight distribution and viscosity, the CTP was mixed with ethanol before the consecutive nitric acid and thermal treatments. The precursor pitches with ethanol, nitric acid, and thermal treatments were easily spinnable, and their spinning and carbon fiber properties were compared to those of air blowing and thermal treated CTP.

Isotropic pitch fibers were stabilized and carbonized for preparing carbon fibers. To optimize the duration and temperature during the stabilization process, a thermogravimetric analysis was conducted. Stabilized fibers were carbonized at 1000, 1500, and 2000℃ in a furnace under a nitrogen atmosphere. An elemental analysis confirmed that the carbon content increased with an increase in the carbonization temperature. Although short graphitic-like layers were observed with carbon fibers heat-treated at 1500 and 2000℃, Raman spectroscopy and X-ray diffraction revealed no significant effect of the carbonization temperature on the crystalline structure of the carbon fibers, indicating the limit of developing an ordered structure of isotropic pitch-based carbon fibers. The electrical conductivity of the carbonized fiber reached 3.9×10⁴S/m with the carbonization temperature increasing to 2000℃ using a four-point method.

To manufacture a carbon/carbon composite the coal tar pitch was used as the matrix precursor and the PAN (polyacrylonitrile)-based carbon fiber was used as the reinforcing material to weave 3-directional preform. For pressure carbonization HIP equipment was used to produce a maximum temperature of 1000℃ and a maximum pressure of 100 MPa. The carbonization was induced by altering the dwell temperature between 250℃ and 420℃, which is an ideal temperature for the moderate growth of the mesophase nucleus that forms within the molten pitch during the pressure carbonization process. The application of high pressure during the carbonization process inhibits the mesophase growth and leads to the formation of spherical carbon particles that are approximately 30 nm in size. Most particles were spherical, but some particles were irregularly shaped. The spread of the carbon particles was larger on the surface of the carbon fiber than in the interior of the matrix pocket.

The structural studies of amorphous isotropic carbon prepared from pyrolysis of phenol formaldehyde resin have been carried out using X-ray diffraction. X-ray diffraction from as prepared sample at 1000℃ and a sample treated at 1900℃ revealed that both are amorphous even though there are small differences in short range order. It is found that both are graphite like carbon (GLC) with predominantly sp2 hybridization. Small angle X-ray scattering results show that as prepared sample mainly consists of thin two dimensional platelets of graphitic carbon whereas they grow in thickness to become three dimensional materials of nano dimensions.