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. SnO2 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.

Research highlights
► Effect of SnO2 deposition on mica substrates for inducing rutile TiO2 was studied.
► Deposition of SnO2 prior to TiO2 was critical in for higher rutile/anatase ratio.
► Heat treatment at 800°C was sufficient for crystallization of 95% rutile TiO2.
► Structure of muscovite mica was preserved by the low temperature crystallization.
► Small amount of SnO2 provides significant increase in gloss of paints.