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Silica nanoparticles (40 nm) were individually and conformally coated with alumina films using atomic layer deposition (ALD) in a fluidized bed reactor. Films were deposited using self-limiting sequential surface reactions of trimethylaluminum and water. Alumina vibrational modes were observed using Fourier-transform infrared spectroscopy (FTIR). X-ray photoelectron spectroscopy (XPS) indicated complete coverage on the surface as the silica features were completely attenuated. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) showed high uniformity of the deposited films. Transmission electron microscopy (TEM) revealed extremely conformal films with an average growth rate of 0.11 nm per cycle. Self-limiting characteristics of ALD allowed primary nanoparticles to be coated as they fluidized as dynamic aggregates.

Primary zirconia nanoparticles were conformally coated with alumina ultrathin films using atomic layer deposition (ALD) in a fluidized bed reactor. Alternating doses of trimethylaluminium and water vapour were performed to deposit Al(2)O(3) nanolayers on the surface of 26 nm zirconia nanoparticles. Transmission Fourier transform infrared spectroscopy was performed ex situ. Bulk Al(2)O(3) vibrational modes were observed for coated particles after 50 and 70 cycles. Coated nanoparticles were also examined with transmission electron microscopy, high-resolution field emission scanning electron microscopy and energy dispersive spectroscopy. Analysis revealed highly conformal and uniform alumina nanofilms throughout the surface of zirconia nanoparticles. The particle size distribution and surface area of the nanoparticles are not affected by the coating process. Primary nanoparticles are coated individually despite their high aggregation tendency during fluidization. The dynamic aggregation behaviour of zirconia nanoparticles in the fluidized bed plays a key role in the individual coating of nanoparticles.

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