The effect of iron ions on the anataseerutile phase transformation of titania (TiO 2 ) in micaetitania pigments Qiang Gao a, b , Xiaomei Wu a, b, * , Yueming Fan a, b a School of Materials Science and Engineering, South China University of Technology, Guangzhou 510641, People’s Republic of China b Key Laboratory of Specially Functional Materials of the Ministry of Education, South China University of Technology, Guangzhou 510641, People’s Republic of China article info Article history: Received 8 October 2011 Received in revised form 13 March 2012 Accepted 28 March 2012 Available online 5 April 2012 Keywords: Pearlescent pigment Anataseerutile transformation Iron ions TiO 2 Photocatalytic Mica abstract Rutile TiO 2 -coated micaetitania pigments were prepared by hydrolysis of titanium tetrachloride in the presence of Fe 3þ . After calcination at 700  C for 2 h, TiO 2 nanolayers in rutile phase were formed on the mica surfaces. The morphology and the anataseerutile transformation were probed by scanning elec- tronic microscopy (SEM) and X-ray diffraction (XRD) respectively. SEM micrographs show that the dopants enhance the growth of particles of TiO 2 thin layers. The change of lattice parameters confirms that Fe 3þ enter anatase structure and affect the anataseerutile transformation. For the iron loading regime studied here, the anataseerutile transformation is inhibited at low dopant levels with respect to undoped titania. While the anataseerutile transformation is promoted as iron loading is increased. Moreover, synthesized pH value also has a pronounced effect on the anataseerutile transformation and a highly acidic environment favors the formation of rutile. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Effect pigments have lustrous, iridescent and angle-dependent optical effects. These pigments are widely applied for functional and decorative purposes, such as optical filters, cosmetics, plastics, printed products, industrial coatings, and car paints for their effects [1e4]. The best known examples are the pearlescent pigments that are based on TiO 2 precipitated onto platelets of mica [5]. There are several approaches for synthesizing micaetitania pigments, such as solegel technique, chemical vapor deposition, and the hydrolysis of titanium tetrachloride [6e8]. Calcinations at 800  Ce900  C convert the amorphous TiO 2 precipitate to crystalline TiO 2 thin layer [9]. Moreover, due to the anatase directing effect of mica [10], anatase and rutile still coexist when the calcination temperature is increased to 1000  C [11]. It is well known that TiO 2 is a polymorphous compound, crystallizing as: rutile, anatase, or brookite. All of them have the same fundamental structural octahedral units with different arrangements [12]. In contrast with the other two phases, rutile TiO 2 is the most stable phase even in strongly acidic or basic conditions [13]. The refractive index of rutile (2.93) is higher than that of anatase (2.49), so that the effect of strong color and luster can be achieved when micaetitania pigments consist of complete rutile layers [11]. Furthermore, rutile has been found to show poor photocatalytic activities in most case [14,15], which may help to solve the problem of ‘chalking’ (photooxidation of surrounding polymeric binders in outdoor weathering initiated by the pigment) that has been besetting the coatings industry [16e18]. For above reasons, rutile modification of titanium dioxide in a pearlescent pigment is more desirable than the anatase modification. Many researches [18e21] have focused on the phase transition behavior and photocatalytic activities of Fe 3þ -doped TiO 2 nano- particles. However, very few studies on the anataseerutile trans- formation with the effect of iron ions for micaetitania pigments have been reported. In this study, micaetitania pigments were synthesized by hydrolysis of titanium tetrachloride and the effect of iron ions on the anataseerutile transformation was investigated. 2. Experimental 2.1. Materials The mica used as the substrate in this study was synthetic mica, supplied by Sanbao Pearl Luster Mica Tech CO., LTD, China. Dry mica flakes were sieved to obtain narrow size distribution. The SEM image of the naked mica shows that the mica powder has a flaky * Corresponding author. School of Materials Science and Engineering, South China University of Technology, Guangzhou 510641, People’s Republic of China. Tel./ fax: þ86 020 87114243. E-mail address: imxmeiwu@scut.edu.cn (X. Wu). Contents lists available at SciVerse ScienceDirect Dyes and Pigments journal homepage: www.elsevier.com/locate/dyepig 0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.dyepig.2012.03.030 Dyes and Pigments 95 (2012) 96e101