Measurement of inherent material density of nanoparticle agglomerates

We describe a new technique to measure the size dependent inherent material density of chain agglomerate particles. Measurements were carried out for diesel soot and aluminum/alumina agglomerate particles in the nanometer size range. Transmission electron microscopy was used to measure the volumes of agglomerate particles that were preselected by mass using an aerosol particle mass analyzer. We found that the density of diesel exhaust particles increased from 1.27 to 1.78 g/cm³ as particle mobility size increased from 50 to 220 nm. When particles are preheated to remove volatile components, the density was 1.77±0.07 g/cm³, independent of particle size. The densities measured after heating correspond to the inherent material density of diesel soot. Measurements with aluminum nanoparticles were made down stream of a furnace where aluminum (Al) was converted to alumina (AI₂O ₃). From measurements of inherent material density we were able to infer the extent of reaction, which varied with furnace temperature.