Characterisation of flame-generated soot and soot-in-oil using electron tomography volume reconstructions and comparison with traditional 2D-TEM measurements

•Electron tomography was used as a technique to characterise carbon black and soot-in-oil.•Flame-generated particle showed an extensive 3D structure.•Soot-in-oil particle was notably two-dimensional.•Morphological parameters varied significantly over the range of viewing angle.•2D calculations of fractal dimension generally underestimate the 3D value.

This work characterises soot nanoparticles by electron tomography using Weighted Back Projection algorithm and appraises the uncertainties in two-dimensional calculations by comparison with 3D parameters for flame-generated soot and diesel soot-in-oil. Bright field TEM was used to capture 2D images of soot. Large uncertainties exist in 2D-measured morphological parameters. The flame-generated particle showed an extensive 3D structure while the soot-in-oil was notably two-dimensional. Morphological parameters of flame-generated soot and diesel soot-in-oil were different; primary particles, volume, and surface area varied significantly over the range of viewing angle, with differences as large as 60%. 2D flame-generated soot volume underestimated 3D measurements by 38%; soot-in-oil 2D- and 3D-derived volumes were within 4%. 2D calculations of fractal dimension generally underestimate the 3D value.