Carbon Black Particle Size: What Does It “Mean”?

Carbon black (CB) fineness has been quantified since the first TEM images of CBs in 1939 revealed the presence of aggregated, spheroidal, size-distributed particles. Since particle size could be measured directly from TEM micrographs, mean particle size (MPS) became a ubiquitous CB fineness descriptor. TEM determination of MPS, however, faces challenges related to the intrinsic morphology of carbon black, details of the measurements, statistical sampling and lack of regulation in the ASTM standard procedure. An exploration of these challenges and their effect on MPS determination is used to demonstrate the strengths and weaknesses of the technique as well as the use of external specific surface area (SSA) to characterize carbon black fineness. While the SSA method is the preferred method for carbon black fineness characterization, the TEM technique is found to be uniquely suited to provide specific distributional information and measure samples where bulk SSA methods are not applicable.