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Titanium dioxide

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itanium dioxide, also known as titanium(IV) oxide or titania (Cl 77891), is the naturally occurring oxide of titanium, chemical formula TiO2. When used as a pigment, it is called titanium white or Pigment White 6.

Natural occurrence


Titanium dioxide occurs in four forms:
rutile, a tetragonal mineral usually of prismatic habit, often twinned;
anatase or octahedrite, a tetragonal mineral of dipyramidal habit;
brookite, an orthorhombic mineral. Both anatase and brookite are relatively rare minerals;
Titanium dioxide (B) or TiO2(B), a monoclinic mineral.

Titanium dioxide occurrences in nature are never pure; it is found with contaminant metals such as iron. The oxides can be mined and serve as a source for commercial titanium. The metal can also be mined from other minerals such as ilmenite or leuxocene ores, or one of the purest forms, rutile beach sand.

Uses


Titanium dioxide is the most widely used white pigment because of its brightness and very high refractive index (n=2.4), in which it is surpassed only by a few other materials. When deposited as a thin film, its refractive index and color make it an excellent reflective optical coating for dielectric mirrors. TiO2 is also an effective opacifier in powder form, where it is employed as a pigment to provide whiteness and opacity to products such as paints, coatings, plastics, papers, inks, foods, and most toothpastes. In cosmetic and skin care products, titanium dioxide is used both as a pigment and a thickener, and in almost every sunblock with a physical blocker, titanium dioxide is found both because of its refractive index and its resistance to discoloration under ultraviolet light. This advantage enhances its stability and ability to protect the skin from ultraviolet light. It is also used in resistance-type lambda probes (a type of oxygen sensor).

Titanium dioxide, particularly in the anatase form, is a photocatalyst under ultraviolet light. The strong oxidative potential of the positive holes oxidizes water to create hydroxyl radicals. It can also oxidize oxygen or organic materials directly. Titanium dioxide is thus added to paints, cements, windows, tiles, or other products for sterilizing, deodorizing and anti-fouling properties and is also used as a hydrolysis catalyst. As TiO2 is exposed to UV light, it becomes increasingly hydrophilic, thus it can be used for anti-fogging coatings or self-cleaning windows. TiO2 incorporated into outdoor building materials can substantially reduce concentrations of airborne pollutants such as volatile organic compounds and NOx.
TiO2 is desired as an agent in remediation of wastewater due to several factors.

1. The process occurs under ambient conditions.
2. The formation of photocyclized intermediate products, unlike direct photolysis techniques, is avoided. 3. Oxidation of the substrates to CO2 is complete.
4. The photocatalyst is inexpensive and has a high turnover.
5. TiO2 can be supported on suitable reactor substrates.
6. The process offers great potential as an industrial technology to detoxify wastewaters.

The Vinland map, the map of America ("Vinland") that was supposedly drawn during mid-15th century based on data from the Viking Age, has been declared a forgery on the basis that the ink on it contains traces of the TiO2-form anatase; TiO2 was not synthetically produced before the 1920s. Recently (1992) a counter-claim has been made that the compound can be formed from ancient ink.

Titanium dioxide is used as a white food dye. In that use, its E number is E171. The white color of toothpaste is that of titanium dioxide. It is also used as a tattoo pigment.

This article is licensed under the GNU Free Documentation License.
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