The effect of tin dioxide (SnO₂) on the anatase-rutile phase transformation of titania (TiO₂) in mica-titania pigments and their use in paint

The synthesis of mica-titania special effect pigment and the effect of rutile promoting additive, tin dioxide (SnO₂), on the phase transformation of titanium dioxide (TiO₂) were investigated. SnO ₂ coating with variable thicknesses on sieved and pre-treated muscovite mica prior to TiO₂ 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 SnO₂ and TiO₂, but the coating of SnO₂ before TiO₂ was found critical in obtaining TiO₂ 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 SnO₂ promotes TiO₂ 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.