Ultrathin coating of particles in fluidized bed using submicron droplet aerosol

Abstract

In this work, we demonstrate that particles can be coated in a fluidized bed with coating solution provided by a novel aerosol generator. Aerosol droplets are smaller than 1μm in volume-based diameter, hence they are very much smaller than droplets in conventional spray fluidized bed processes (around 40μm). A proof-of-principle experiment with 30% aqueous coating solution of sodium benzoate and γ-Al2O3 core particles in 150mm fluidized bed fed with droplet aerosol supplied from the chamber side is presented. To simultaneously coat and dry the particles, inlet of fluidization air was at 50°C. Moreover, Monte Carlo simulations of coating with small aerosol and large spray droplets were conducted. Due to dramatically smaller building blocks, ultrathin particle coating of high-resolution (very small layer thickness) can be attained with the new aerosol process, with the potential of even going nanoscale. Full coverage of particles is reached substantially faster than in the conventional process, so that material demand is much lower and sensitive materials can be processed in short residence time. Solids yield of around 30% was much higher than expected, that is considered to be technically viable and may be enhanced by the recycling of entrained solids or better equipment design.