Effect of La 3+ on evolution of TiO 2 coating layers on lamellar sericite and their pigmentary properties

Abstract

TiO 2-coated sericite powders were prepared by the chemical deposition method starting from lamellar sericite and TiCl 4 in the presence of La 3+. After calcination at 900 °C for 1 h, the resultant TiO 2 nanoparticles on the sericite surfaces exist in anatase phase. The light scattering indexes of the TiO 2-coated lamellar sericite powders are dozens of times higher than those of the naked lamellar sericite powders, varying with different contents of La 3+. The presence of La 3+ in the deposition solution is beneficial to the formation of the small-sized anatase TiO 2 nanoparticles. The presence of La 3+ also favors the formation of the dense and uniform island-like TiO 2 coating layers in a large range of the mass ratio of TiO 2 to sericite from 5% to 20%. XPS analysis shows that when La 3+ is absent in the reaction solution, TiO 2 coating layers anchor on the sericite surface via Ti—O—Si and Ti—O—Al bonds. The presence of La 3+ causes the formation of Si—O—La and Al—O—La bonds on the sericite surface and Ti—O—La bond on the surface of TiO 2 coating layers.