American Association for Aerosol Research - Abstract Submission

AAAR 38th Annual Conference
October 5 - October 9, 2020

Virtual Conference

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Structure and Dynamics of Fractal-like Particles Made by Agglomeration and Sintering

EIRINI GOUDELI, Maximilian L. Eggersdorfer, University of Melbourne

     Abstract Number: 342
     Working Group: Nanoparticles and Materials Synthesis

Abstract
Aerosol synthesis of nanoparticles is a versatile process for production of commodities like titania, carbon black and fumed silica at scale. A critical design criterion for aerosol reactors is the high temperature particle residence time, which determines the nanoparticle growth by gas and surface reaction, coagulation and sintering. Typically, the chemistry is so rapid that coagulation and sintering dominate the particle growth and, thus, their structure that can impact significantly the material performance (e.g., catalytic or optical properties). Therefore, knowing the collision frequency and sintering time is necessary to model particle growth mechanisms accurately, which are currently modeled by making a priori assumptions on the particle structure.

Here, the growth of silica nanoparticles by agglomeration and viscous flow sintering is studied from free molecular to transition regime at high temperatures by discrete element method simulations. The effect of temperature on the aggregate mobility and gyration radii, particle morphology and collision frequency function is elucidated as function of the number of primary particles. The ratio between the characteristic sintering time and characteristic collision time controls the particle size and structure, quantified by the mass fractal dimension. The effect of this ratio of characteristic times on aggregate morphology is illustrated at various temperatures. Finally, when sintering is negligible, the overall collision frequency is 90% larger than that predicted by the classic Fuchs collision kernel for monodisperse agglomerates in the near free molecular and transition regime. For comparable coagulation and sintering rates, where aggregates with sinter bonds are formed, the overall collision frequency increases an enhancement of <90% is observed.