(417f) On-Line Characterization of Nanoparticles During Gas-Phase Synthesis

Real-time aerosol characterization is important for monitoring continuous nanoparticle producing processes as primary and agglomerate particle size determine product properties significantly. Sampling these aerosols, however, is all but trivial. Particle concentrations can be as high as 10^18 per kg of gas, requiring an enormous dilution to quench particle growth processes. The sampling probe has to withstand temperatures up to ~1500 K and possibly corrosive environments. Therefore, mostly ex-situ methods have been used to determine particle size and morphology in such conditions.

Here, an in-situ method for nearly real-time determination of average agglomerate mass, volume, mobility and structure along with the constituent primary particle size is employed. It is performance-tested in a flame spray aerosol reactor for production of zirconia nanoparticles (Gröhn et al., 2012). A sampling probe for continuous extraction and immediate dilution of the hot and highly concentrated aerosol was designed and constructed. Online characterization of the diluted aerosol is achieved by combining a differential mobility analyzer (DMA) with an aerosol particle mass analyzer (APM) and applying a power-law correlation to derive average primary particle size as proposed by Eggersdorfer et al. (2012).

Primary particle growth was shown to be completed shortly above the burner as a constant primary particle diameter was observed for all radial and downstream axial positions. The average agglomerate size increased with axial distance from the burner. However, larger agglomerates were observed at the fringes of the aerosol plume attributed to prolonged residence time due to lower gas velocity there. Results were compared against off-line particle size characterization by nitrogen adsorption and thermophoretic sampling/transmission electron microscopy. The method could also be applied successfully in continuous pilot-scale manufacture of zirconia nanoparticles, providing instantaneous quality control.

References:

Eggersdorfer, M.L., Gröhn, A.J., Sorensen, C.M., McMurry, P.H. and Pratsinis, S.E. (2012), J. Colloid. Interface Sci. 387, 12 - 23.

Gröhn, A.J., Pratsinis, S.E., and Wegner, K. (2012), Chem. Eng. J. 191, 491 - 502.