anatase

Anatase is a mineral and one of the three mineral phases of titanium dioxide (TiO2). It crystallizes in the tetragonal system and typically forms small, well-shaped crystals that may be transparent to translucent with a pale color. Anatase is metastable at ambient temperatures and slowly converts to the more stable rutile phase on heating above roughly 600–700 °C, depending on impurities and particle size. It has a Mohs hardness around 5.5 and a density near 3.9 g/cm3.

Geologically, anatase occurs in titanium-rich hydrothermal veins and pegmatites and as an alteration product of titanite in metamorphic rocks. It is commonly associated with rutile and brookite, and with ilmenite and titanite.

As a commercially important form of TiO2, anatase is used as a white pigment in paints, plastics, paper, and coatings. Although rutile pigments are more prevalent for outdoor use due to greater stability, anatase is used in some interior coatings and in nano-structured applications; it also serves as a photocatalyst in environmental remediation and in dye-sensitized solar cells. In nanoparticle form, anatase exhibits high photocatalytic activity and is studied for antimicrobial properties and solar energy applications.

In synthesis, anatase can be produced synthetically by hydrothermal, precipitation, or sol-gel methods. Crystallographic notes: anatase is tetragonal, space group I41/amd, with lattice constants a ≈ 3.785 Å and c ≈ 9.515 Å. It is one of three TiO2 polymorphs, the others being rutile and brookite.