Titanium dioxide
Titanium dioxide, also known as
titanium(IV) oxide or
titania, is the naturally occurring
oxide of
titanium, chemical formula Ti
O2. When used as a
pigment, it is called
titanium white,
Pigment White 6, or
CI 77891.
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 TiO
2(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
leucoxene ores, or one of the purest forms,
rutile beach sand.
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. TiO
2 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 TiO
2 is exposed to UV light, it becomes increasingly
hydrophilic, thus it can be used for anti-fogging coatings or self-cleaning windows. TiO
2 incorporated into outdoor building materials can substantially reduce concentrations of airborne pollutants such as
volatile organic compounds and
NOx.
TiO
2 is desired as an agent in remediation of wastewater due to several factors.# The process occurs under ambient conditions. # The formation of photocyclized intermediate products, unlike direct photolysis techniques, is avoided. # Oxidation of the substrates to CO
2 is complete. # The photocatalyst is inexpensive and has a high turnover. # TiO
2 can be supported on suitable reactor substrates. # 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 TiO
2-form
anatase; TiO
2 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.
*
International Chemical Safety Card 0338*
NIOSH Pocket Guide to Chemical Hazards*
A description of the Vinland map*
A description of TiO2 photocatalysis*
An article on photocatalytic paint*
Crystal structures of the three forms of TiO2* Kutal, C., Serpone, N. (1993). Photosensitive Metal Organic Systems: Mechanistic Principles and Applications. American Chemical Society, Washington D.C
