Effects Of Mineral Surface Properties On The Structure And Performance Of Mineral/TiO₂ Composite Particle Materials

The mineral/TiO₂ composite particles materials （M/TCPM）, a core （mineral）-shell （crystalline TiO₂） type composite particle materials, are new-style white pigments developed in recent years and have been widely used as the substitutes of titanium dioxide. However, there is little about effects of the surface properties of core minerals on the structures and performances of M/TCPM as well as the reaction mechanism between mineral and TiO₂. These researches are important in utilizing synergistic effect of core minerals together with TiO₂, optimizing and regulating performances of M/TCPM.In this work, nonmetallic minerals with different surface properties such as unsaturated substances, functional groups forms, and particles morphologies are used as the core materials to prepare M/TCPM by mechano-chemical method in water medium. The effects of surfaces properties of minerals on the performances of M/TCPM and the reaction mechanisms of mineral between TiO₂ are studied.Pigmentary properties of M/TCPM with different core minerals are tested. In terms of mineral, the order of the hiding powers of M/TCPM can be described as sericite>brucite>wollastonite>calcium carbonate>calcined kaolin>barite, and the similarities to the color of titanium dioxide are described as wollastonite>calcined>kaolin>calcium carbonate>brucite>barite>sericite. M/TCPM are similar to titanium dioxide in pigmentary properties when the proportion of TiO₂ is 50%.The effect of mineral surface properties and particle morphologies on pigmentary properties of M/TCPM are studied. Unsaturated substances of the mineral, surface functional groups and mineral particle morphologies are the main factors resulting in the differences of pigment properties of M/TCPM. The stronger the hydroxylation degree of unsaturated ion is （or directly as hydroxyl component）, the more obvious the anisotropy of mineral particle morphology is, the better the pigmentary properties of M/TCPM.The binding strengths and action properties between core minerals and TiO₂ are also studied by ultrasonic treatment and FTIR analysis. From the comparison of the changes in pigment properties and structures of M/TCPM after ultrasonic treatment and the physical forces and ultrasonic forces between TiO₂ and core minerals, it can be concluded that the core minerals combine chemically with TiO₂ through dehydroxylation with OH groups on TiO₂ particles surfaces except barite.Fractal dimension and 3d fractal dimension calculation of M/TCPM show that the fractal dimensions of the minerals increase after combining with TiO₂. That is, the complexities of M/TCPM are more obvious than that of single mineral particles. This implies that TiO₂ particles have coated on the surface of core minerals and made their surfaces rough significantly.