Titanium dioxide, also known as titanium(IV) oxide or titania, is the naturally occurring oxide of titanium, chemical formula TiO
2. When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. Generally, it is sourced from ilmenite, rutile and anatase. It has a wide range of applications, including paint, sunscreen and food coloring. When used as a food coloring, it has E number E171. World production in 2014 exceeded 9 million metric tons.[4][5][6] It has been estimated that titanium dioxide is used in two-thirds of all pigments, and the oxide has been valued at $13.2 billion.[7]
Contents
1 Occurrence
2 Production
2.1 Specialized methods
3 Applications
3.1 Pigment
3.2 Thin films
3.3 Sunscreen and UV blocking pigments
3.4 Other uses
4 Research
4.1 Photocatalyst
4.2 Nanotubes
5 Health and safety
5.1 Environmental waste introduction
6 Trivia
7 See also
8 References
9 External links
Occurrence
Titanium dioxide occurs in nature as the well-known minerals rutile, anatase and brookite, and additionally as two high pressure forms, a monoclinic baddeleyite-like form and an orthorhombic α-PbO2-like form, both found recently at the Ries crater in Bavaria. One of these is known as akaogiite and should be considered as an extremely rare mineral.[8][9][10] It is mainly sourced from ilmenite ore. This is the most widespread form of titanium dioxide-bearing ore around the world. Rutile is the next most abundant and contains around 98% titanium dioxide in the ore. The metastable anatase and brookite phases convert irreversibly to the equilibrium rutile phase upon heating above temperatures in the range 600–800 °C (1,112–1,472 °F).[11]
Titanium dioxide has eight modifications – in addition to rutile, anatase, and brookite, three metastable phases can be produced synthetically (monoclinic, tetragonal and orthorombic), and five high-pressure forms (α-PbO2-like, baddeleyite-like, cotunnite-like, orthorhombic OI, and cubic phases) also exist:
Form Crystal system Synthesis
Rutile Tetragonal
Anatase Tetragonal
Brookite Orthorhombic
TiO2(B)[12] Monoclinic Hydrolysis of K2Ti4O9 followed by heating
TiO2(H), hollandite-like form[13] Tetragonal Oxidation of the related potassium titanate bronze, K0.25TiO2
TiO2(R), ramsdellite-like form[14] Orthorhombic Oxidation of the related lithium titanate bronze Li0.5TiO2
TiO2(II)-(α-PbO2-like form)[15] Orthorhombic
Akaogiite (baddeleyite-like form, 7 coordinated Ti)[16] Monoclinic
TiO2 -OI[17] Orthorhombic
Cubic form[18] Cubic P > 40 GPa, T > 1600 °C
TiO2 -OII, cotunnite(PbCl2)-like[19] Orthorhombic P > 40 GPa, T > 700 °C
The cotunnite-type phase was claimed by L. Dubrovinsky and co-authors to be the hardest known oxide with the Vickers hardness of 38 GPa and the bulk modulus of 431 GPa (i.e. close to diamond's value of 446 GPa) at atmospheric pressure.[19] However, later studies came to different conclusions with much lower values for both the hardness (7–20 GPa, which makes it softer than common oxides like corundum Al2O3 and rutile TiO2)[20] and bulk modulus (~300 GPa).[21][22]
The oxides are commercially important ores of titanium. The metal can also be mined from other minerals such as ilmenite or leucoxene ores, or one of the purest forms, rutile beach sand. Star sapphires and rubies get their asterism from rutile impurities present in them.[23]