## 2 Experimental Procedure  
### Raw Materials and Preparation  
In this study, commercial coal-based isotropic coke (POSCO MC MATERIALS, Jeonnam, Republic of Korea) was used as a filler, while commercial coal tar pitch (Rain Carbon, Stamford, CT, USA) was employed as a binder. The average powder particle size (D50) of the filler was 6.57 \(\upmu\)m; the properties of the selected binder are summarized in Table 1.  
The mixing ratio of filler and binder is related to the properties of the graphite block. For the particle size of the filler used in this study, a weight ratio of 75:25 was found to be the most appropriate ratio [16]. The filler and binder were mixed via ball milling at a weight ratio of 75:25, and the mixture was then subjected to kneading. The kneading process was conducted for 30 min at 170 \({}^{\circ}\)C, which was higher than 110 \({}^{\circ}\)C, the softening point of the binder pitch. The kneaded mixture underwent a milling process before use. After the milling process, the kneaded powder was injected into a mold with dimensions of 10 mm \(\times\) 10 mm \(\times\) 50 mm and compression molding was then conducted. The obtained green bodies were carbonized in a tube furnace, where they were heated at a rate of 2 \({}^{\circ}\)C/min from room temperature to 1000 \({}^{\circ}\)C and then maintained at that temperature for 1 h. During the \begin{table}
\begin{tabular}{c c} \hline \hline  & **Properties of Binder Pitch** \\ \hline Softening point (\({}^{\circ}\)C) & 110–120 \\ \hline Toluene insoluble (\%) & 22–28 \\ \hline Quinoline insoluble (\%) & 4–8 \\ \hline Ash content (\%) & \textless{}0.3 \\ \hline Fixed Carbon (\%) & \textgreater{}54 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Properties of binder pitch. process, an inert atmosphere was maintained using N\({}_{2}\) to prevent oxidation. In this study, the same conditions as described above were applied to all specimens during carbonization. More specifically, to determine the effect of compression pressure, specimens were subjected to compression molding for 1 min under varying compression pressures of 70, 100, and 130 MPa. As a result, green bodies fabricated under different compression pressures were prepared for the subsequent carbonization process. The maximum possible pressure of the compressor employed in this study was 150 MPa. However, to avoid any instability during the forming process, the maximum pressure was set to 130 MPa. A previous study by our research team reported the fabrication of carbon blocks under a pressure of 100 MPa [17]. In general, during low-pressure forming, it is challenging to achieve sufficient pressure-induced binding between coke and pitch. Consequently, the resulting green bodies are less likely to maintain their shape. As such, in this study 100 MPa was defined as the reference pressure level, and two other conditions were set by adding or deducting 30 MPa. Overall, the compression pressures were set to 70, 100, and 130 MPa. Additionally, to analyze the effect of holding time during compression molding, the holding time was varied between 1, 2, and 3 min at a compression pressure of 130 MPa. The resulting green bodies were subjected to carbonization to obtain carbon blocks with varying holding times. Generally, the holding time ranges from a few seconds to a few minutes, depending on the type and amount of powder and the shape of molds applied [18]. If the holding time is too short during carbonization, it is less likely that the original shape of green bodies will be maintained after they transform into carbon blocks. In this study, it was observed that the green bodies were able to maintain their shape when the holding time was set to 1 min, regardless of the compression pressure. At a compression pressure of 130 MPa, the holding time was varied between 1, 2, and 3 min. As the holding time increased to 2 or 3 min, the bulk density and porosity of the carbon blocks remained almost unchanged. However, there was a degradation in their mechanical and electrical properties with increased holding time.