The effect of tin dioxide (SnO 2) on the anatase-rutile phase transformation of titania (TiO 2) in mica-titania pigments and their use in paint

Abstract

The synthesis of mica-titania special effect pigment and the effect of rutile promoting additive, tin dioxide (SnO 2), on the phase transformation of titanium dioxide (TiO 2) were investigated. SnO 2 coating with variable thicknesses on sieved and pre-treated muscovite mica prior to TiO 2 coating yields a pearlescent pigment with higher rutile-to-anatase ratio. Different than what is reported in a few cases, not the co-deposition of SnO 2 and TiO 2, but the coating of SnO 2 before TiO 2 was found critical in obtaining TiO 2 coatings consisting of 95% rutile phase at 1073 K. A calcination temperature as low as 1073 K resulted in the preservation of substrate’s structural integrity. Scanning electron microscopy analyses showed that SnO 2 promotes TiO 2 growth at certain nucleation points rather than random nucleation points. Mica-titania pigments were incorporated in the acrylic based paints and gloss and hardness characteristics of the paint specimens were measured. Specimens with increased rutile content showed improved gloss.