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%.
Bibliographical noteFunding Information:
Parts of this work were carried out in the University of Minnesota I.T. Characterization Facility, which receives partial support from NSF through the NNIN program. The authors also acknowledge the Graduate School at the University of Minnesota for the Doctoral Dissertation Fellowship awarded to Weon Gyu Shin.
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- Mass-mobility diameter scaling exponent
- Particle alignment