Analysis of pore formation and development in carbon blacks activated in a CO2 gas atmosphere through microstructural observation

The present study analyzed the pore formation and development process in carbon black that was activated by CO2 gas and the effect of the burn-off (BO) ratio on the process, particularly based on changes in the surface shape and internal microstructure. The activation process was performed as follows. Carbon blacks were injected into a horizontal tube furnace when the inside temperature reached 1000 °C. Carbon black samples with different BOs, i.e., 7.2%, 15.4%, 30.4%, 48.2%, 59.9%, and 83.2%, were prepared by varying the activation time. The microstructure of the activated samples was observed and examined using SEM and TEM. The results showed that pore passages were first created on the surface of the primary particles of the carbon black, and then the inner portion of the carbon black with a lower degree of crystallinity started to be activated, thereby causing inner pores to be formed. These inner pores then started to grow and coalesce into larger pores, thereby causing the crystallite layers in the inner portion of the carbon black to be activated. The changes in the microstructure of the carbon black during the activation reaction were attributable to the carbon black manufacturing process, in which the nucleation and growth of the primary particles of the carbon black occurred within a very short period of time. Thus, the crystallization of the inner portion was suppressed, and therefore, the degree of crystallinity was lower in the inner portion than in the outer portion.