Passivation of pigment-grade TiO₂ particles by nanothick atomic layer deposited SiO₂ films

Pigment-grade TiO₂ particles were passivated using nanothick insulating films fabricated by atomic layer deposition (ALD). Conformal SiO ₂ and Al₂O₃ layers were coated onto anatase and rutile powders in a fluidized bed reactor. SiO₂ films were deposited using tris-dimethylaminosilane (TDMAS) and H₂O₂ at 500°C. Trimethylaluminum and water were used as precursors for Al ₂O₃ ALD at 177°C. The photocatalytic activity of anatase pigment-grade TiO₂ was decreased by 98% after the deposition of 2 nm SiO₂ films. H₂SO₄ digest tests were performed to exhibit the pinhole-free nature of the coatings and the TiO ₂ digest rate was 40 times faster for uncoated TiO₂ than SiO₂ coated over a 24 h period. Mass spectrometry was used to monitor reaction progress and allowed for dosing time optimization. These results demonstrate that the TDMAS-H₂O₂ chemistry can deposit high quality, fully dense SiO₂ films on high radius of curvature substrates. Particle ALD is a viable passivation method for pigment-grade TiO₂ particles.