Characterization of carbon fractal-like aggregates by size distribution measurements and theoretical calculations

The structural characteristics of carbon nanoparticles synthesized by a spark discharge source were investigated by combined measurements of polydisperse number and Fuchs surface-area distributions against equivalent particle mobility and aerodynamic diameters. The number and Fuchs surface area distribution measurements were conducted by a scanning mobility particle sizer (SMPS) and a cascade epiphaniometer (CEPI), respectively. The CEPI-measured total Fuchs surface area and the Fuchs surface area calculated from SMPS number distributions were found to be in reasonable agreement (average absolute difference 28%), suggesting that the momentum-transfer diameter may be approximated by the mass-transfer diameter. The measured total Fuchs surface area of polydisperse distributions was reasonably reproduced by the Fuchs surface area of a monodisperse distribution (average absolute difference 26%). A fitting procedure was used to obtain the effective density mobility diameter relationship. The generated carbon aggregates, composed of primary particles of average diameter of 12.7 +/- 2.5 nm, were determined to obey a fractal-like power law with a mass mobility fractal dimension D-m = 2.14 and a prefactor k(m) = 1.06, in good agreement with theoretical calculations. Experimental measurements were compared to various theoretical models for the number of primary particles, the dynamic shape factors, and the effective density.