Aerosol fluidized bed coating: Exploring the impact of process conditions on process yield, coating coverage and thickness

Abstract

Aerosol droplets are used to coat fluidized particles in this work. Coating experiments utilizing aerosol droplets (with a mean diameter of around 1μm) were performed under different process conditions to explore their impact on process yield, as well as on coating coverage. Core materials were glass and porous γ-Al2O3, which had mean diameters of 653μm and 610μm, respectively. Sodium benzoate (NaB) solution and silicon dioxide (SiO2) nanosuspension were used as the coating liquid. After sampling, particle pictures were taken by a scanning electron microscope and analyzed using image processing to determine the coating coverage. To simulate the coating process and determine, for each experiment, a factor for preferential deposition on already occupied positions, Monte Carlo simulations were used. Also, some particles were cut in the middle to measure coating layer thickness. Intraparticle coating thickness distribution from Monte Carlo simulations coarsely matches the measured thickness from cut particles. Results show that the process yield, coating coverage, and preference factor are affected by experimental conditions such as expanded bed height, fluidization air temperature, atomizing pressure, the number of aerosol inlets, as well as the surface potential of core particles. This study is first to examine the impact of surface charge of different core materials on droplet deposition. In an experiment with SiO2 nanosuspension, γ-Al2O3 cores could be coated quite uniformly with SiO2 nanoparticles with a layer thickness of ca. 1.1μm. This shows the potential of aerosol droplet deposition as a novel semi-wet method for coating large particles with nanoparticles without using any binders.