Titanoxid

Titanoxid, commonly known as titanium dioxide (TiO2), is an inorganic compound widely used as a white pigment. It occurs in nature as the minerals anatase, rutile and brookite, with anatase and rutile forming the majority of synthetic pigments. Rutile is the more thermodynamically stable phase at room temperature; anatase is more photoactive and often used in photocatalysis.

Properties

TiO2 is a white, non-flammable powder with a high refractive index (around 2.5) and strong opacity. Densities are approximately 4.23 g/cm3 for rutile and 3.9 g/cm3 for anatase. The bandgap is wide, about 3.0 eV for rutile and 3.2 eV for anatase, making TiO2 transparent in the visible range but active to ultraviolet light. It is chemically inert, insoluble in water and most acids, and exhibits excellent stability under light and heat.

Production

Industrial TiO2 is produced from titanium-containing minerals such as ilmenite or rutile. The two main commercial routes are the sulfate process and the chloride process. In the chloride process, titanium tetrachloride (TiCl4) is oxidized to TiO2, followed by pigment milling and surface treatment to enhance dispersibility and opacity. The sulfate process uses sulfuric acid to extract TiO2 from ilmenite.

Applications

The primary use is as a white pigment in paints, coatings, plastics, rubber and paper, providing brightness, opacity and durability. It is also used in cosmetics and sunscreens for UV protection. TiO2-based photocatalysts enable applications in self-cleaning surfaces, air and water purification, and certain photovoltaic devices such as dye-sensitized solar cells, particularly in the anatase form.

Safety and regulation

TiO2 is regarded as relatively low-toxicity as a bulk material, but inhalation of fine dust can irritate the lungs and require protective measures. Consumer products typically use surface-treated particles to enhance safety and performance. In German-language contexts, Titanoxid is the common term for TiO2.