Effect of substrate on the phase transformation of TiO2 in pearlescent pigment

The TiO2/substrate pearlescent pigments were prepared by the hydrolysis of TiOCl2 on the substrate followed by a calcinations process. The natural mica (muscovite), synthetic mica (fluorophlogopite) and α-alumina flake were selected as the substrates for pearlescent pigments. The effect of substrate on the anatase to rutile (A–R) phase transformation of TiO2 was studied. The A–R phase transformation of TiO2 during the preparation of pearlescent pigments and their proportion in the TiO2 layer have been analyzed by XRD measurements. The phase compositions of TiO2 layer in each pearlescent pigment are quite different depending on the substrates. The TiO2 layer deposited on α-alumina has higher rutile fraction than those on the natural and synthetic mica. The XPS analysis showed that the cations originally present in the substrates diffused into the TiO2 layer. The TiO2 layer deposited on α-alumina contains Al, while those on the natural and synthetic mica substrates contain Si and K in addition to Al. The metal cations diffusing from the substrate into TiO2 layer might retard the A–R phase transformation of TiO2. The suppressing effect on the A–R transformation of TiO2 by mixed cations seems to be much stronger than that of single cation, resulting in relatively higher rutile fraction in the case of TiO2 layer deposited on α-alumina.