Chemical composition of titanium dioxide pigments depends on the type of used raw material, method of production and grade of pigment. The type of raw material and method of production are of decisive influence on the level of impurities in the ready product.
Manufacturers make every effort to minimise – despite technological limitations – the level of impurities originating from titanium-bearing raw materials or from other chemicals used during manufacturing process in the pigment.
This results from the fact that many impurities, being even traces, negatively influence the pigment properties, and the optical properties above all. Such low level of impurities and non-toxicity of titanium dioxide itself enables use titanium dioxide in products having contact with food, and sometimes directly as food additive (E171).
Apart from titanium dioxide and associated traces of impurities, the composition of commercial titanium dioxide pigments includes components intentionally introduced by manufacturers, targeted to improve pigment properties, the most often in the scope of its dispersibility and resistance to outdoor conditions. These components include substances built-into crystal structure or deposited on the surface of pigment particles at the following stages:
- modification of crystallographic structure of anatase or rutile,
- inorganic surface treatment,
- organic surface treatment.
Due to the numerous methods of execution of the above stages and the variety of substances used, the type and the content of particular admixtures in relation to TiO2is very different.
Depending on participation of used admixtures, the content of TiO2 in commercially available titanium dioxide pigments ranges from 80% in case of highly surface-treated pigments up to 99 % in case of pigments without surface treatment. Important is also the fact that the kind and the quantity of applied admixtures and the method of execution of surface treatment decide about the final properties of the pigment, and thus also its applications. A selection of proper pigment for specific application is extremely important.