Oxidative degradation of carbon blacks with nitric acid (I)—Changes in pore and crystallographic structures

Furnace and acetylene blacks were oxidized with nitric acid in order to obtain some insight into the mechanism of oxidative degradation of carbon blacks. Changes in the pore and crystallographic structures of the carbon blacks in the course of oxidation were examined by nitrogen adsorption, X-ray diffraction, scanning tunneling microscopy (STM) and transmission electron microscopy (TEM). A furnace black with an undeveloped crystallographic structure was easily oxidized, and at an early oxidation stage many pores were formed in the particles, leading to a high surface area. As the oxidation proceeded the surface area became negligible because the carbon black particles changed into masses resulted from coagulation of crystallites and carbon layers broken up by oxidation. For an acetylene black with a developed crystallographic structure, oxidation proceeded at the peripheries of the crystallites, and many crevasses were formed and developed into the inner parts of particles. Furthermore, the oxidative degradation proceeded preferentially in the inside of the particles with a less developed carbon structure and left a hollow structure in which the holes were opened to the outside through the crevasses formed in the shells. The presence of the holes and the crevasses were observed with TEM and STM, respectively.