Innovative titanium dioxide‐kaolin mixed pigments performance in anticorrosive paints

Kaolin is a soft, white mineral mainly composed of coarse‐ to fine‐grained, plate‐like aluminum silicate particles. As kaolin assists with desired rheological properties that help maintain proper dispersion and provide bulk to the product, it is used as an important extender in paint manufacture. It can be used to reduce the amount of expensive pigments, such as titanium dioxide. In spite of these uses, kaolin has the disadvantage of having coarse particles and low hiding power. The purpose of this paper is to introduce a new class of pigments based on kaolin as a core and titanium dioxide as the shell.

In the work reported in this paper, kaolin was used as a core covered with a surface layer of titanium dioxide comprising the shell in order to combine their properties and get over kaolin's disadvantages, besides enhancing its corrosion protection properties. The pigments prepared were characterised using X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Deposition of titanium dioxide on the surface of kaolin was confirmed by Energy‐dispersive X‐ray analysis (EDAX) and X‐ray fluorescence (XRF) techniques. Pigment properties were estimated according to American standard testing methods (ASTM) methods and then were incorporated in anticorrosive paint formulations based on medium oil alkyd resin. The physico‐mechanical and corrosion properties of dry paint films were determined according to ASTM methods.

The tests revealed that the concentration of titanium dioxide layer deposited on kaolin surface was inversely proportional to the anticorrosive behaviour of these pigments.

The pigments can be applied in other polymer composites, e.g. rubber and plastics as filler and reinforcing agent.

The pigments prepared are eco‐friendly that can replace other expensive pigments. These pigments can compensate for the presence of titanium dioxide in paint formulations successfully, and thus lower the costs. The main advantage of these pigments is that they combine the properties of both of their counterparts, they are of lower cost, and they also overcome the disadvantages of both its counterparts, e.g. low hiding power of kaolin, photochemical activity of titanium dioxide. Also, they can be applied in other industries other than paints, e.g. paper, rubber and plastics composites.