Spectral properties of carbon black

The internal structure of carbon black particles considerably influences the optical behavior of the material, apart from the shape and agglomeration state of the primary particles. In this paper the correlation between internal structure and spectral behavior of carbon black is investigated experimentally. The carbon blacks were produced by resistive heating of graphite electrodes and condensation in a cooling gas atmosphere. The internal structure of the primary carbon black particles was investigated by high-resolution transmission electron microscopy, electron energy loss spectroscopy, C-13 NMR spectroscopy, and Raman spectroscopy. The primary particles were found to consist of bent or plane structural subunits. The UV pi - pi* absorption feature of the produced carbon blacks varies in position between 196 and 265 nm depending on the state of bending of the graphene layers in the subunits of particles and/or the dimensions of the plane graphitic microcrystallites and the incorporation of hydrogen. The different curvature radii of the graphene layers or the sizes of microcrystallites can be summarized by an integral dimension like the ratio of sp(2)/sp(3) hybridized carbon atoms. In the mid-infrared spectral region, the absolute value of the absorption coefficient re is dominated by a continuous absorption due to free charge carriers which are also influenced by the ratio of sp(2)/sp(3) hybridized carbon in the primary particles. The appearance of prominent bands is related to the existence of functional groups, like C-H-n, C=O and/or C-O-C. (C) 1999 Elsevier Science B.V. All rights reserved.