## 2 Results  
### Polarization Microscope Analysis  
Figure 1 shows polarized microscopic images of the needle coke and the binder pitch polymer. Figure 1a is polarized microscopic images of the binder polymer, indicating that the binder pitch was generally isotropic without an anisotropic part. Figure 1b shows the needle coke before being pulverized, indicating that the overall structure was a flow domain structure and that the bulk needle coke had cracks inside. Figure 1c shows the needle coke after being pulverized by a jet-mill. The pulverized needle coke was not spherical but had a flake shape. Even after being pulverized, the needle coke particles had an anisotropic structure with the same color as the bulk needle coke. Since the needle coke and the binder pitch polymer on those structures were used to manufacture the green blocks, it was expected that a clear laminated structure would be found on the inside of the green blocks, due to the difference in shape of the two materials. The cross-sections of the green blocks manufactured by a hot-press under different pressure conditions were observed using a polarization microscope, and the images are shown in Figure 2. The images in Figure 2 indicate that the needle coke particles in the cross-sections were aligned in the direction perpendicular to the hot-press axis in all four green blocks. The needle coke particles were aligned in the direction perpendicular to the hot-press axis, even under low pressure. This is because the needle coke particles were flowable due to the binder pitch polymer, which was softened by the hot-press procedure at 200 \({}^{\circ}\)C. Figure 3 is a cross-sectional image of the graphite block manufactured by thermal treatment at 2800 \({}^{\circ}\)C, indicating that the needle coke particles were aligned in the direction perpendicular to the hot-press axis even after the thermal treatment at 2800 \({}^{\circ}\)C. Figure 4 provides additional evidence of the alignment. Figure 1: Optical structure of material; (**a**) binder pitch polymer; (**b**) bulk needle coke; (**c**) crushed needle coke. Figure 3: Optical structure of graphite block; (**a**) B_N-G, (**b**) B_5-G, (**c**) B_10-G, (**d**) B_20-G.  
Figure 2: Optical structure of green block: (**a**) B_N, (**b**) B_5, (**c**) B_10, (**d**) B_20. In general, for graphite blocks to have high thermal conductivity, it is advantageous that the flake-shaped needle coke particles are aligned in the direction perpendicular to the hot-press axis. To determine whether the molded structure of the manufactured graphite blocks permitted high thermal conductivity, the images in Figures 2 and 3 were used to quantify the alignment structure of the needle coke particles, using the method shown in Figure 4a. The lateral size of the needle coke particles and their angle relative to the horizontal direction were measured, and then the angle was converted into cos (\(\theta\)) and substituted into the following equation:  
\[\textit{Particle orientation}\ =\ \frac{\sum(\textit{particle size}\ (\mu m))\times\cos(\theta)}{\textit{Total particle number}} \tag{1}\]  
Figure 4b,c shows the particle orientation values of the green blocks and the graphite blocks, calculated using the Equation. Both Figure 4b,c indicates that, as the \(\theta\) of the particles was nearer to \(0^{\circ}\), the particles were laterally aligned in the direction that was more perpendicular to the direction of the hot-press axis. The particle orientation and \(\theta\) values of the green blocks increased as the pressure increased. However, the values of the B_10 and B_20 samples were similar, showing that there was not a significant difference in the values above a certain pressure. The particle orientation decreased in all the samples by 10.47 to 2.46% after graphitization.