## 3 Results and Discussion
### Effect of Compression Pressure  
To analyze the effects of compression pressure, green bodies were fabricated at a kneading temperature of 170 \({}^{\circ}\)C under varying compression pressures of 70, 100 and 130 MPa for 1 min. These green bodies were then carbonized, and the bulk density, porosity, flexural strength, Shore hardness, electrical resistivity, and microstructure of the resulting carbon blocks were analyzed. Figure 3a shows changes in the bulk density and porosity of the carbon blocks with respect to compression pressure. As the compression pressure increased, the bulk density increased, and the porosity decreased. At a compression pressure of 130 MPa, the highest bulk density was achieved at 1.391 g/cm\({}^{3}\), along with the lowest porosity at 27.9%. [PERSON] [22] reported that, in ceramics, elevating the pressure applied during compression molding induced the rearrangement of powder particles, leading to increased packing rates. This structural change, in turn, resulted in increased bulk density and  
Figure 2: Images of isotropic coke and kneaded particles. decreased porosity in the resulting molded bodies. The observation in Figure 3, indicating an increase in bulk density and a decrease in porosity with increasing compression pressure, can be attributed to the rearrangement of the filler and binder. This interpretation aligns with the findings of the previous study mentioned above. Figure 3: Curves representing mechanical properties as a function of compression pressure (**a**) bulk density and porosity, **(b**) flexural strength and Shore hardness, and (**c**) electrical resistivity. Figure 3b shows the effects of compression pressure on the flexural strength and Shore hardness of the carbon blocks. At a compression pressure of 70 MPa, both the flexural strength and Shore hardness were the lowest. The flexural strength at 100 MPa was comparable to that at 130 MPa. Many previous studies have reported a correlation between pores and flexural strength. The flexural strength of carbon blocks depends on pore type and size. When subjected to compression pressure, carbon blocks undergo stress concentration within their pores, which ultimately act as defects [23; 24; 25]. An increase in compression pressure induces the rearrangement of fillers and binders, resulting in variations in the shapes and sizes of pores. This microstructural change, in turn, affects the flexural strength of the resulting carbon blocks. The microstructural observations in Figures 4 and 5 support this mechanism. Figure 4: OM images of carbon blocks with respect to compression pressure at a magnification of 100\(\times\). It is known that the Shore hardness of carbon blocks is affected by porosity but it is difficult to find papers that clearly interpret the correlation. Additionally, in some papers, it was found that there was no correlation between Shore hardness and porosity [25]. The Shore hardness of carbon blocks needs to consider the size of the indenter. Shore hardness was highest at 100 MPa and decreased again at 130 MPa. This phenomenon can be explained by the microstructure in Figure 5. Shore hardness is a principle that measures the height at which a specimen rises after  
Figure 5: SEM images of carbon blocks with respect to compression pressure at magnifications of 1000\(\times\) and 5000\(\times\). -resolution. At 70 MPa, the Shore hardness is low because there are large pores inside the carbon block, and at 100 MPa, the size of the pores decreases and the Shore hardness increases. As the Shore hardness decreases again at 130 MPa, the area where the kneaded particles are connected is thought to have low Shore hardness. Figure 3c shows changes in the electrical resistivity of the carbon blocks with respect to compression pressure. Overall, as the compression pressure increased, the electrical resistivity decreased.