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.

The present study examined changes in surface shape and pore size observed in carbon black particles isothermally oxidized in an air atmosphere according to their burn-off ratio. Carbon black materials were fed into a horizontal tubular furnace in an air atmosphere when the inside temperature reached 600 °C. Subsequently, while changing the isothermal oxidation time, carbon black samples with different burn-off ratios were obtained, i.e., 10.5, 20.0, 30.4, 41.0, 49.9, 59.8, 71.1, and 81.0%. The scanning electron microscope analysis revealed that the observed carbon black particles were in the form of aggregated primary particles, and that there was no change in the particle size of these primary particles as the burn-off process proceeded. The latter observation supported the observation that pores were formed in the carbon black samples during the burn-off process. Notably, the Brunauer–Emmett–Teller analysis exhibited hysteresis curves, indicating that the corresponding adsorption isotherms were of IV-type. It was also found that the area of the hysteresis curves increased as the burn-off process proceeded. The specific surface area of the raw carbon black sample was 58.00 m2/g, while that of the 81.0% sample was about 4.1 times the figure at 240.27 m2/g. The total pore volume VT was 0.17 cm3/g for the raw sample, and it was much higher for the 81.0% sample at 0.58 cm3/g. The transmission electron microscope analysis showed that the raw carbon black particles had a spherical shape with a smooth surface, but inner pores were not observed. In the 49.9% sample, pores with a size of about 5 nm were observed inside carbon black particles. Notably, the size of the pores observed in the 81.0% sample was about 20 nm and the large pores were created by the collapsing and merging of the smaller pores by oxidation.

Carbon blacks (CBs) have been widely used as reinforcing materials in advanced rubber composites. The mechanical properties of CB-reinforced rubber composites are mostly controlled by the extent of interfacial adhesion between the CBs and the rubber. Surface treatments are generally performed on CBs to introduce chemical functional groups on its surface. In this study, we review the effects of various surface treatment methods for CBs. In addition, the preparation and properties of CB-reinforced rubber composites are discussed.

The development of hollow carbon balls by CO2 oxidation of two types of carbon blacks was studied. Super P (SP) and Denka Black (DB) were used for this study. Specificsurface area (SSA), structural parameters, and microstructures were examined using Brunauer, Emmett and Teller apparatus, X-ray diffraction spectroscopy, and transmission electron microscope (TEM), respectively. The SSAs of both oxidized carbon blacks increased after oxidation. The SSAs of raw DB and SP were 73 m2/g and 60 m2/g, respectively. Maximum SSAs of oxidized DB and SP were 152 m2/g and 253 m2/g, respectively. The d002 of DB and SP showed almost no change after oxidation. The Lc of raw DB (38Å) and SP (19Å) increased with increasing weight loss. The Lc of SP increased up to 254 at 96% weight loss. The SSA increased about twice in DB (148 m2/g) and about four times in SP (254 m2/g) after 3 h oxidation compared with the original carbon blacks. Through TEM observation the outer parts of the oxidized carbon blacks showed a rigid shell structure and the inner parts looked empty. Generally it looked like an angular soccer ball, so we named it ‘hollow carbon ball.’ It is expected that the hollow carbon ball can be used as catalyst supports.

Rubber reinforcing carbon black N330 was treated by physical activation under CO2 to different degrees of burn-off. The mechanical properties indicating the reinforcement of SBR (Styrene-Butadiene Rubber) vulcanizates filled by activated carbon blacks, such as tensile strength, modulus at 300% strain and elongation at break were determined. During CO2 activation of fresh carbon blacks, the development of microporous structure caused an increase of extremely large specific surface area and the porosity turned out to be an increasing function of the degree of burn-off. The tensile strength and modulus at 300% of activated carbon blacks filled rubber composites were improved at lower loading ratios of 20 and 30 phr, but decreased drastically after 30 phr, which is considered that it might be difficult to get a fully dispersed rubber mixture at higher loading ratios for fillers having very large specific surface areas. However, the Electromagnetic Interference (EMI) shielding effectiveness of SBR rubber composites having activated carbon black at 74% yield were improved at a large extent when compared to those having raw carbon black and increased significantly as a function of increasing loading ratio.

Properties of carbon blacks and carbon black/SBR rubber composites filled by surface modified carbon blacks were examined. Although the specific surface area of carbon blacks increased after the surface modifications with heat, acid, and base, there were no obvious changes in resistivity. The composites filled by heat treated carbon blacks showed a higher tensile strength and elongation than those filled by raw blacks. The acid and base treated carbon blacks filled composites also showed higher tensile strength but similar elongation values with those filled by raw blacks. With increasing loading ratio, both tensile strength and elongation increased, and appeared a maximum value at 30-40 phr. Modulus at 300% strain remained increasing with further loading of carbon blacks. At the same loading, the heat treated black filled composites showed similar modulus values with composites filled by raw blacks but for base and acid treated black filled composites much higher values were obtained. After the surface modification, the functional groups which played an important role in reinforcement action were changed.