Titanium dioxide

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Titanium dioxide
Image:Rutile-unit-cell-3D.png
Chemical name	Titanium dioxide Titanium(IV) oxide
Other names	Titania Rutile Anatase Brookite
Chemical formula	Ti O₂
SMILES	O=Ti=O
Molecular mass	79.87 g/mol
Appearance	White solid
CAS number	[13463-67-7]
HS number	Titanium oxides: 2823.00 2823.00.10.000(anatase) 2823.00.90.000(others)
Properties
Density	4.23 g/cm³
Melting point	1870 °C (3398 °F)
Boiling point	2972 °C (5381.6 °F)
Dielectric Constant ε_r	80-110
Heat Capacity	298.13 J/(mol °C)
Heat Conductivity	6.531 W/(m K)
Lin. Coeff. Therm Exp.	8.19 °C<^-1
Elastic Module	244 GPa
Hardness	5-6.5 Mohs
El. Resistance	3*10⁵ Ω @ 773 K
Ref. Index(n_g,n_m,n_p)	Rutile: 2.9467,-,2.6506 α-rutile: 2.908,-,2.621 Anatase: 2.5688,-,2.6584 γ-anatase: 2.448,-,2.261 Brookite: 2.809,-,2.677 α-brookite: 2.7004,2.5843,2.5831
Solubility	Insoluble
Thermodynamic data
Δ_fH^o_gas	−249 kJ/mol
Δ_fH^o_liquid	−879 kJ/mol</td>
Δ_fH^o_solid	−944 kJ/mol</td>
S^o_solid	51 J/mol·K</td>
Hazards
MSDS	External MSDS
EU classification	not listed
NFPA 704	Image:NFPA 704.svg 0 1 0
Flash point	non-flammable
RTECS number	XR2775000
Supplementary data page
Structure and properties	n, ε_r, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Other cations	Titanium(II) oxide Titanium(III) oxide Titanium(III,IV) oxide Zirconium dioxide Hafnium dioxide
Disclaimer and references

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.

1 Natural occurrence
2 Uses
3 Titanium dioxide and a dating expertise
4 See also
5 External links

[edit] 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 leucoxene ores, or one of the purest forms, rutile beach sand.

[edit] Uses

[edit] As a pigment of high refringence

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. Used as a white food dye, it has E number E171. In cosmetic and skin care products, titanium dioxide is used both as a pigment and a thickener. It is also used as a tattoo pigment.

This pigment is used extensively in plastics and other applications for its UV resistant properties where it acts as a UV reflector.

In ceramic glazes titanium dioxide acts as an opacifier and seeds crystal formation. 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.

[edit] As a photocatalyst

Titanium dioxide, particularly in the anatase form, is a photocatalyst under ultraviolet light. Although recently is has been found that titanium dioxide when spiked with nitrogen ions, will also react as a photocatalyst under lamp 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. It is also used in the Graetzel cell, a type of chemical solar cell.

Titanium dioxide has potential for use as a source of energy: as a photocatalyst, it can carry out hydrolysis, ie, break water into hydrogen and oxygen. Were the hydrogen collected, it could be used as a fuel. The efficiency of this process can be greatly improved by doping the oxide with carbon, as described in "Carbon-doped titanium dioxide is an effective photocatalyst" [1].

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 nitrogen oxides.

[edit] For wastewater remediation

TiO₂ 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 CO₂ is complete.
The photocatalyst is inexpensive and has a high turnover.
TiO₂ can be supported on suitable reactor substrates.
The process offers great potential as an industrial technology to detoxify wastewaters.

[edit] Other uses

It is also used in resistance-type lambda probes (a type of oxygen sensor).

[edit] Titanium dioxide and a dating expertise

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.