What is the Difference Between Anatase Rutile and Brookite?

Anatase, rutile, and brookite are three different structures of titanium dioxide (TiO2) minerals. The key differences between anatase, rutile, and brookite are:

1. Crystal Structure: Anatase has a tetragonal unit cell with four TiO2 units, while rutile has a tetragonal unit cell with two TiO2 units, and brookite has an orthorhombic unit cell with eight TiO2 units.
2. Band Gap: Anatase is an indirect band gap semiconductor, while rutile and brookite are direct band gap semiconductors.
3. Photocatalytic Activity: Anatase typically exhibits higher photocatalytic activity than rutile and brookite due to its longer lifetime of photoexcited electrons and holes and lighter average effective mass of photogenerated electrons and holes.
4. Stability: Anatase is the stable TiO2 phase at low pressure and temperature, while rutile occupies a higher pressure and temperature sector. Brookite is often an early-forming phase in some geological settings, followed by anatase, and finally rutile as a later alteration product of both.

In summary, anatase, rutile, and brookite are three different structures of titanium dioxide minerals with distinct crystal structures, band gaps, and photocatalytic activities. They form at different pressures and temperatures, and their stability depends on the specific conditions of their formation.

Comparative Table: Anatase Rutile vs Brookite

Here is a table comparing the differences between anatase, rutile, and brookite:

Anatase and rutile are two different phases of titanium dioxide (TiO2) with distinct properties. Rutile is the most stable form of TiO2, while anatase and brookite are metastable forms. They have different crystal structures, optical properties, and appearances. Anatase is a tetragonal crystal system with a relative density of 4.2-4.3 and a refractive index of 2.71, while rutile has a square crystal system, a relative density of 3.9-4.25, and a refractive index of 2.52. Rutile is optically positive, whereas anatase is optically negative.

Brookite is another form of TiO2 with an orthorhombic unit cell and eight TiO2 units. It is more stable than anatase for crystal sizes larger than 11 nm, while rutile is the most stable phase for sizes larger than 35 nm.