S. Sigmund, M. Yu, J. Meyer, G. Kasper

Aerosol Science and Technology, 2014, 48, 142-149

An aerosol-based process for coating the surface of arbitrary “carrier” particles with other types of (smaller) “coating” particles via mutual electrostatic attraction is described. Its practical viability was tested by depositing negatively charged 12-nm palladium particles on 250-nm silica spheres carrying a charge of approximately +40 units each. At respective concentrations of 3 to 8 x 10⁶ particles per cm³ (with a charge fraction of about 25%) and 1 x 10⁴ particles per cm³, the deposition process runs to completion (i.e., to neutralization of the carrier particles) within less than a minute. Comparative estimates show that electrostatically enhanced deposition rates are up to 50 times higher than purely thermal collisions. Transmission electronmicrographs show a fairly uniform distribution of coating particles across the surface of the carrier particles. The electrostatic coating kinetics were determined experimentally via the charge loss of the carrier particles and compared also to numerical simulations using Zebel’s model for electrostatic enhancement of the collision kernel. Measured rates were generally within 10-15% of the simulations, except for the very early stages of attachment (the first 10 s), where agreement was found to be rather sensitive to the coating particle concentration, possibly due to space charge effects.