Tandem Differential Mobility Analyzers (TDMA) were used along with TEM analysis to determine agglomerate volume, scaling exponents for both mass-mobility diameter (Dfm) and friction coefficient-number of primary particles (η) for the mobility diameter in the range 30-300. nm. The larger agglomerates with dm=250 and 300. nm require a temperature of 800 °C and a sintering time of 0.7. s to form a spherical shape compared to 600 °C for a mobility diameter of 150. nm. It is shown that the 3% decrease in mobility size of the 250 and 300. nm agglomerates with increasing sintering temperature (600-800 °C) is a result of a morphology change from an ellipsoid to a sphere during the sintering process. The effect of sublimation on the sintered particle size is negligible with less than a 0.5% decrease in diameter for a 300. nm mobility diameter agglomerate at 800 °C. The TDMA results show that Dfm is not dependent on mobility size range and that η is dependent on the size range. Both results are counter to predictions based on free molecular models. These results confirm previous results obtained using a DMA together with an aerosol particle mass analyzer (APM) and are shown to have about a factor of two smaller uncertainty. It is also experimentally demonstrated that the agglomerate particles with dm=300. nm are partially aligned in the electric field of DMA. The correction for a random orientation results in a significant decrease in Dfm by 3.5% and a significant increase in η by 3%.
- Mass-mobility diameter scaling exponent
- Particle alignment