(328b) Passivated Pigment-Grade TiO2 Nanoparticles By Atomic Layer Deposition Barrier Films Using A Scalable Fluidized Bed Reactor

Atomic layer deposition (ALD) of nanothick SiO₂ barrier films is utilized here for the passivation of ultrafine and nanosized TiO2 pigment particles. Conformal, pinhole-free films have been successfully deposited in a scalable fluidized bed reactor. Both anatase and rutile substrates were coated for this work. Films as thin as 2 nm, as verified by HRTEM, eliminated 98% of the photoactivity as compared to the uncoated substrate. Sulfuric acid digestion studies were performed using ICP-AES to monitor the dissolution rate of the TiO₂ core. The 2 nm SiO₂ films prevented > 99% of the TiO₂ cores from dissolving, which also verified the conformal, pinhole-free nature of these films. In situ mass spectrometry was used to monitor reaction progress and to prevent excess precursor usage and process time. This residual gas analysis technique is advantageous to minimize process costs and is applicable to fluidized bed or similar flow-type reactor configurations at any scale. The fabrication of colored, passivated pigments is also possible by first depositing an appropriate number of atomic layers of chromophore-based transition metal oxides (i.e. Al, Cr, Mn, Ni, V, etc.); then the passivating film can be applied in situ. SiO₂ ALD films are very efficient and can be further optimized to meet the needs of all aspects of the pigment industry. Surface passivation can be extremely economical in large-scale batch processing using the process control measures presented in this work.