In this study, a graphite block is fabricated using artificial graphite processing byproduct and phenolic resin as raw materials. Mechanical and electrical property changes are confirmed due to the preforming method. After fabricating preforms at 50, 100, and 150 MPa, CIP molding at 150 MPa is followed by heat treatment to prepare a graphite block. 150UP-CIP shows a 12.9% reduction in porosity compared with the 150 MPa preform. As the porosity is decreased, the bulk density, flexural strength, and shore hardness are increased by 14.9%, 102.4%, and 13.7%, respectively; and the deviation of density and electrical resistivity are decreased by 51.9% and 34.1%, respectively. Therefore, as the preforming pressure increases, the porosity decreases, and the electrical and mechanical properties improve.

The change in the open porosity of bulk graphite as a function of the uniaxial molding pressure during manufacturing is studied using artificial graphite powder. Subsequently, the graphite is impregnated to determine the effect of the open porosity on the impregnation efficiency and to improve the density of the final bulk graphite. Bulk graphite is manufactured with different uniaxial molding pressures after mixing graphite powder, which is the by-product of processing the final graphite products and phenolic resin. The bulk density and open porosity are measured using the Archimedes method. The bulk density and open porosity of bulk graphite increase as the molding pressure increases. The open porosity of molded bulk graphite is 25.35% at 30 MPa and 29.84% at 300 MPa. It is confirmed that the impregnation efficiency increases when the impregnation process is performed on a specimen with large open porosity. In this study, the bulk density of bulk graphite molded at 300 MPa is 11.06% higher than that before impregnation, which is the highest reported increase. Therefore, it is expected that the higher the uniaxial pressure, the higher the density of bulk graphite.

In the manufacturing of bulk graphite, pores produced by vaporization and discharge of volatile materials in binders during carbonization reduce the density of bulk graphite, which adversely affects the electrical conductivity, strength and mechanical properties. Therefore, an impregnation process is introduced to fill the pores and increase the density of bulk graphite. In this study, bulk graphite is prepared by varying the viscosity of the impregnant. The microstructure of bulk graphite is observed. The flexural strength and electrical resistivity are measured. As the viscosity of the impregnants decreases and the number of impregnations increases, it is shown that the number of pores decreases. The density before impregnation is 1.62 g/cm3. The density increases to 1.67 g/cm3 and porosity decreases by 18.6 % after three impregnations using 5.1 cP impregnant, resulting in the best pore-filling effect. After three times of impregnation with a viscosity of 5.1 cP, the flexural strength increases by 55.2 % and the electrical resistivity decreases by 86.76 %. This shows that a slight increase in density due to the pore-filling effect improves the properties of bulk graphite.

Pores produced by carbonization in bulk graphite process degrade the mechanical and electrical properties of bulk graphite. Therefore, the pores of bulk graphite must be reduced and an impregnation process needs to be performed for this reason. In this study, bulk graphite is impregnated by varying the viscosity of the impregnant. The pore volume and pore size distribution, according to the viscosity of the impregnant, are analyzed using a porosimeter. The total pore volume of bulk graphite is analyzed from the cumulative amount of mercury penetrated. The volume for a specific pore size is interpreted as the amount of mercury penetrating into that pore size. This decreases the cumulative amount of mercury penetrating into the recarbonized bulk graphite after impregnation because the viscosity of the impregnant is lower. The cumulative amount of mercury penetrating into bulk graphite before impregnation and after three times of impregnation with 5.1cP are 0.144 mL/g and 0.125 mL/gm, respectively. Therefore, it is confirmed that the impregnant filled the pores of the bulk graphite well. In this study, the impregnant with 5.1 cP, which is the lowest viscosity, shows the best effect for reducing the total pore volume. In addition, it is confirmed by Raman analysis that the impregnant is filled inside the pores. It is confirmed that phenolic resin, the impregnant, exists inside the pores through micro-Raman analysis from the inside of the pore to the outside.

Milled carbon fiber (mCF) was prepared by a ball milling process, and X-ray diffraction (XRD) diffractograms were obtained by a 2θ continuous scanning analysis to study mCF crystallinity as a function of milling time. The raw material for the mCF was polyacrylonitrile- based carbon fiber (T700). As the milling time increased, the mean particle size of the mCF consistently decreased, reaching 1.826 μm at a milling time of 18 h. The XRD analysis showed that, as the milling time increased, the fraction of the crystalline carbon decreased, while the fraction of the amorphous carbon increased. The (002) peak became asymmetric before and after milling as the left side of the peak showed an increasingly gentle slope. For analysis, the asymmetric (002) peak was deconvoluted into two peaks, less-developed crystalline carbon (LDCC) and more-developed crystalline carbon. In both peaks, Lc decreased and d002 increased, but no significant change was observed after 6 h of milling time. In addition, the fraction of LDCC increased. As the milling continued, the mCF became more amorphous, possibly due to damage to the crystal lattices by the milling.