(354d) Passivation Of Pigment-Grade TiO2 By SiO2 Atomic Layer Deposition In A Fluidized Bed Reactor

King, D. M. - Presenter, University of Colorado, Boulder
Akhtar, K. M. - Presenter, Millennium Chemicals Inc.
Liang, X. - Presenter, University of Colorado, Boulder
Weimer, A. W. - Presenter, University of Colorado at Boulder

The pigment industry is a ~ $5 billion/year industry, of which a significant portion of process cost is to effectively passivate the highly photoactive and acid degradable TiO2 substrate. Atomic layer deposition (ALD) of nanothick SiO2 films is utilized here for the passivation of TiO2 nanoparticle pigments. 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. H2SO4 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 verifies 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. 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.