Porosity and crystallinity dynamics of carbon black during internal and surface oxidation

Abstract

The structure of carbon black (CB) is investigated during its oxidation by O2 at 550 and 800 °C by thermogravimetric analysis, microscopy, N2 adsorption and X-ray diffraction (XRD). That way, the dynamics of its porosity and crystallinity during surface and internal oxidation are elucidated, for the first time to the best of our knowledge. At 800 °C, oxidation takes place largely on the CB surface. This increases the CB specific surface area, SSA, from 240 to about 453 m2/g, closely following the classic shrinking particle model and hardly affects the porosity and crystallinity of CB. At 550 °C, O2 diffuses and reacts with the bulk of CB particles forming pores with radius smaller than 2 nm after 25 and 50% conversion. At higher conversions, these small pores fuse together resulting in hollow CB particles with high SSA, up to 939 m2/g. Fractal and XRD analyses of the resulting pore network reveals that internal oxidation at 550 °C reduces the interlayer distance of the crystallites constituting the CB, compacting its pore network. This increases the pore fractal dimension, Dfp, from 2.43 up to about 2.7, in good agreement with the Dfp measured during diesel soot oxidation. The dynamics of CB porosity and crystallinity quantified in detail here can assist the design of new highly porous CB grades and activated carbons as well as battery materials.