Structure and dynamics of fractal-like particles made by agglomeration and sintering

The growth of silica nanoparticles by agglomeration and viscous flow sintering is studied from free molecular to transition regime by off-lattice event-driven (ED) simulations. Coagulation by simultaneous agglomeration and sintering takes place at high temperature environments, where sintering and collision rates are comparable. The effect of temperature on aggregate mobility and gyration radii, particle morphology, and collisional enhancement is elucidated. The ratio between the characteristic sintering time and characteristic collision time controls the particle size and structure, quantified by the mass fractal dimension. The aggregate morphology depends solely on the ratio of characteristic times and is insensitive to the process temperature. When sintering is negligible, the overall collision frequency is 90% larger than that predicted by the classic Fuchs collision kernel for monodisperse agglomerates, in agreement with experiments. The ED-obtained quasi-self-preserving size distributions are consistent with mobility size distributions measured in hot-wall reactors and flame sprays.