Evolution of TiO2 coating layers on lamellar sericite in the presence of La3+ and the pigmentary properties

TiO(2)-coated sericite powders were prepared by the chemical deposition method starting from lamellar sericite and TiCl(4) in the presence or absence of La(3+) cations. After calcination at 900 degrees C for 1 h, the resultant TiO(2) nanoparticles on the sericite surfaces existed in anatase phase. The light scattering indexes of the TiO(2)-coated lamellar sericite powders were dozens of times higher than that of the naked lamellar sericite powders. The presence of La(3+) in the deposition solution was beneficial to the formation of the small-sized anatase TiO(2) nanoparticles, resulting in the formation of the dense and uniform island-like TiO(2) coating layers in a large range of the weight ratios of TiO(2) to sericite from 5% to 20%. The TiO(2)-coated lamellar sericite powders prepared in the presence of La(3+) had higher light scattering index than that prepared in the absence of La(3+). XPS analysis shows that when La(3+) cations were absent in the reaction solution, TiO(2) coating layers anchored at the sericite surface via the Ti-O-Si and Ti-O-Al bonds. The presence of La(3+) cations caused the formation of Si-O-La and Al-O-La bonds at the sericite surface and Ti-O-La bond at the surface of TiO(2) coating layers. After coating TiO(2) on the sericite surface, the yellowness of the TiO(2)-coated sericite powders obviously increased and the brightness slightly decreased. (C) 2008 Elsevier B.V. All rights reserved.