Titanium dioxide

From Wikipedia, the free encyclopedia
  (Redirected from Titanium Dioxide)
Jump to: navigation, search
Titanium dioxide
IUPAC name
Titanium dioxide
Titanium(IV) oxide
Other names
Titania
Rutile
Anatase
Brookite
Identifiers
CAS number 13463-67-7 YesY
PubChem 26042
ChemSpider 24256 YesY
UNII 15FIX9V2JP YesY
KEGG C13409 N
ChEMBL CHEMBL1201136 N
RTECS number XR2775000
Jmol-3D images Image 1
Properties
Molecular formula TiO2
Molar mass 79.866 g/mol
Appearance White solid
Density 4.23 g/cm3
Melting point

1843 °C
Boiling point

2972 °C
Refractive index (nD) 2.488 (anatase)
2.583 (brookite)
2.609 (rutile)
Hazards
MSDS ICSC 0338
EU classification Not listed
NFPA 704
NFPA 704.svg
0
1
0
Flash point Non-flammable
Related compounds
Other cations Zirconium dioxide
Hafnium dioxide
Related titanium oxides Titanium(II) oxide
Titanium(III) oxide
Titanium(III,IV) oxide
Related compounds Titanic acid
 N(what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Titanium dioxide, also known as titanium(IV) oxide or titania, is the naturally occurring oxide of titanium, chemical formula TiO2. When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. It has a wide range of applications, from paint to sunscreen to food colouring. When used as a food colouring, it has E number E171.

Contents

[edit] Occurrence

Titanium dioxide occurs in nature as 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.[1][2] The most common form is rutile,[3] which is also the equilibrium phase at all temperatures.[4] The metastable anatase and brookite phases both convert to rutile upon heating.[3][5] Rutile, anatase and brookite all contain six coordinated titanium.

Titanium dioxide has eight modifications – in addition to rutile, anatase and brookite there are three metastable forms produced synthetically (monoclinic, tetragonal and orthorombic), and five high pressure forms (α-PbO2-like, baddeleyite-like and cotunnite-like):

Form Crystal system Synthesis
rutile tetragonal
anatase tetragonal
brookite orthorhombic
TiO2(B)[6] monoclinic Hydrolysis of K2Ti4O9 followed by heating
TiO2(H), hollandite-like form[7] tetragonal Oxidation of the related potassium titanate bronze, K0.25TiO2
TiO2(R), ramsdellite-like form[8] orthorhombic Oxidation of the related lithium titanate bronze Li0.5TiO2
TiO2(II)-(α-PbO2-like form)[9] orthorhombic
baddeleyite-like form, (7 coordinated Ti)[10] monoclinic
TiO2 -OI[11] orthorhombic
cubic form[12] cubic
TiO2 -OII, cotunnite(PbCl2)-like[13] orthorhombic

The naturally occurring 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. Star sapphires and rubies get their asterism from rutile impurities present in them.[14]

Titanium dioxide (B) is found as a mineral in weathering rims on tektites and perovskite and as lamellae in anatase from hydrothermal veins and has a relatively low density.[15]

Spectral lines from titanium oxide are prominent in class M stars, which are cool enough to allow molecules of this chemical to form.

[edit] Production

Crude titanium dioxide is purified via converting to titanium tetrachloride in the chloride process. In this process, the crude ore (containing at least 70% TiO2) is reduced with carbon, oxidized with chlorine to give titanium tetrachloride; i.e., carbothermal chlorination. This titanium tetrachloride is distilled, and re-oxidized in a pure oxygen flame or plasma at 1500–2000 K to give pure titanium dioxide while also regenerating chlorine.[16] Aluminium chloride is often added to the process as a rutile promotor; the product is mostly anatase in its absence.

Another widely used process utilizes ilmenite as the titanium dioxide source, which is digested in sulfuric acid. The by-product iron(II) sulfate is crystallized and filtered-off to yield only the titanium salt in the digestion solution, which is processed further to give pure titanium dioxide. Another method for upgrading ilmenite is called the Becher Process. One method for the production of titanium dioxide with relevance to nanotechnology is solvothermal Synthesis of titanium dioxide.

Titanium oxide nanotubes, SEM image.

[edit] Nanotubes

Anatase can be converted by hydrothermal synthesis to delaminated anatase inorganic nanotubes[17] and titanate nanoribbons which are of potential interest as catalytic supports and photocatalysts. In the synthesis, anatase is mixed with 10 M sodium hydroxide and heated at 130 °C for 72 hours. The reaction product is washed with dilute hydrochloric acid and heated at 400 °C for another 15 hours. The yield of nanotubes is quantitative and the tubes have an outer diameter of 10 to 20 nm and an inner diameter of 5 to 8 nm and have a length of 1 μm. A higher reaction temperature (170 °C) and less reaction volume gives the corresponding nanowires.[18]

[edit] Applications

[edit] Pigment

Titanium dioxide is the most widely used white pigment because of its brightness and very high refractive index (n = 2.7), in which it is surpassed only by a few other materials. Approximately 4 million tons of pigmentary TiO2 are consumed annually worldwide. When deposited as a thin film, its refractive index and colour make it an excellent reflective optical coating for dielectric mirrors and some gemstones like "mystic fire topaz". 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, medicines (i.e. pills and tablets) as well as most toothpastes. In paint, it is often referred to offhandedly as "the perfect white", "the whitest white", or other similar terms. Opacity is improved by optimal sizing of the titanium dioxide particles.

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

Titanium dioxide is often used to whiten skimmed milk; this has been shown statistically to increase skimmed milk's palatability.[19]

Titanium dioxide is used to mark the white lines on the tennis courts of the All England Lawn Tennis and Croquet Club, best known as the venue for the annual grand slam tennis tournament The Championships, Wimbledon.[20]

The exterior of the Saturn V rocket was painted with titanium dioxide; this later allowed astronomers to determine that J002E3 was the S-IVB stage from Apollo 12 and not an asteroid.

[edit] Sunscreen and UV absorber

In cosmetic and skin care products, titanium dioxide is used as a pigment, sunscreen and a thickener. It is also used as a tattoo pigment and in styptic pencils. Titanium dioxide is produced in varying particle sizes, oil and water dispersible, and with varying coatings for the cosmetic industry. This pigment is used extensively in plastics and other applications for its UV resistant properties where it acts as a UV absorber, efficiently transforming destructive UV light energy into heat.

Titanium dioxide is found in almost every sunscreen with a physical blocker because of its high refractive index, its strong UV light absorbing capabilities and its resistance to discolouration under ultraviolet light. This advantage enhances its stability and ability to protect the skin from ultraviolet light. Sunscreens designed for infants or people with sensitive skin are often based on titanium dioxide and/or zinc oxide, as these mineral UV blockers are believed to cause less skin irritation than other UV absorbing chemicals. The titanium dioxide particles used in sunscreens have to be coated with silica or alumina, because titanium dioxide creates radicals in the photocatalytic reaction. These radicals are carcinogenic, and could damage the skin.

[edit] Photocatalyst

TiO fibers and spirals.

Titanium dioxide, particularly in the anatase form, is a photocatalyst under ultraviolet (UV) light. Recently it has been found that titanium dioxide, when spiked with nitrogen ions or doped with metal oxide like tungsten trioxide, is also a photocatalyst under either visible or UV light.[21] 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 its sterilizing, deodorizing and anti-fouling properties and is used as a hydrolysis catalyst. It is also used in dye-sensitized solar cells, which are a type of chemical solar cell (also known as a Graetzel cell).

The photocatalytic properties of titanium dioxide were discovered by Akira Fujishima in 1967[22] and published in 1972.[23] The process on the surface of the titanium dioxide was called the Honda-Fujishima effect.[22] Titanium dioxide has potential for use in energy production: as a photocatalyst, it can

In 1995 Fujishima and his group discovered the superhydrophilicity phenomenon for titanium dioxide coated glass exposed to sun light.[22] This resulted in the development of self-cleaning glass and anti-fogging coatings.

TiO2 incorporated into outdoor building materials, such as paving stones in noxer blocks or paints, can substantially reduce concentrations of airborne pollutants such as volatile organic compounds and nitrogen oxides.[26]

A photocatalytic cement that uses titanium dioxide as a primary component, produced by Italcementi Group, was included in Time's Top 50 Inventions of 2008.[27]

TiO2 offers great potential as an industrial technology for detoxification or remediation of wastewater due to several factors.

  1. The process occurs under ambient conditions very slowly; direct UV light exposure increases the rate of reaction.
  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.

[edit] Electronic data storage medium

Researchers at the University of Tokyo, Japan have created a 25 terabyte titanium oxide-based disc.[28]

[edit] Other applications

Synthetic single crystals of TiO2

[edit] Health and safety

Ambox scales.svg
 This article has been nominated to be checked for its neutrality. Discussion of this nomination can be found on the talk page. (March 2011)

Titanium dioxide is incompatible with strong oxidizers and strong acids.[34] Violent or incandescent reactions may occur with metals (fused and very electropositive) (e.g. aluminium, calcium, magnesium, potassium, sodium, zinc and lithium).[35]

Titanium dioxide accounts for 70% of the total production volume of pigments worldwide. It is widely used to provide whiteness and opacity to products such as paints, plastics, papers, inks, foods, and toothpastes. It is also used in cosmetic and skin care products, and it is present in almost every sunblock, where it helps protect the skin from ultraviolet light.

Many sunscreens use nanoparticle titanium dioxide (along with nanoparticle zinc oxide) which does get absorbed into the skin.[36][37] The effects on human health are not yet well understood.[38]

Titanium dioxide dust, when inhaled, has recently been classified by the International Agency for Research on Cancer (IARC) as an IARC Group 2B carcinogen possibly carcinogenic to humans.[39] The findings of the IARC are based on the discovery that high concentrations of pigment-grade (powdered) and ultrafine titanium dioxide dust caused respiratory tract cancer in rats exposed by inhalation and intratracheal instillation.[40] The series of biological events or steps that produce the rat lung cancers (e.g. particle deposition, impaired lung clearance, cell injury, fibrosis, mutations and ultimately cancer) have also been seen in people working in dusty environments. Therefore, the observations of cancer in animals were considered, by IARC, as relevant to people doing jobs with exposures to titanium dioxide dust. For example, titanium dioxide production workers may be exposed to high dust concentrations during packing, milling, site cleaning and maintenance, if there are insufficient dust control measures in place. However, it should be noted that the human studies conducted so far do not suggest an association between occupational exposure to titanium dioxide and an increased risk for cancer. The safety of the use of nano-particle sized titanium dioxide, which can penetrate the body and reach internal organs, has been criticized.[41] Studies have also found that titanium dioxide nanoparticles cause genetic damage in mice.[42]

Researchers, manufacturers, and international organizations such as OECD are actively working to improve our knowledge about nano-sized titanium dioxide. The titanium dioxide industry associations in the U.S. and in Europe support responsible work, particularly with respect to understanding potential health effects in humans. Titanium dioxide pigments have been manufactured for more than 70 years, and sub-pigmentary or nano-sized titanium dioxide has been manufactured for more than 50 years. No adverse health effects attributed to exposure to titanium dioxide have been reported in major epidemiological studies of workers in the titanium dioxide industry. Animal studies citing adverse effects such as ‘genetic damage in mice’ imply that the effects seen apply to humans. Although the effects noted may be interesting data points, relevance to humans has not been established.[43]

[edit] See also

[edit] References

  1. ^ El, Goresy; Chen, M; Dubrovinsky, L; Gillet, P; Graup, G (2001). "An ultradense polymorph of rutile with seven-coordinated titanium from the Ries crater.". Science 293 (5534): 1467–70. doi:10.1126/science.1062342. PMID 11520981. 
  2. ^ El Goresy, Ahmed; Chen, Ming; Gillet, Philippe; Dubrovinsky, Leonid; Graup, GüNther; Ahuja, Rajeev (2001). "A natural shock-induced dense polymorph of rutile with α-PbO2 structure in the suevite from the Ries crater in Germany". Earth and Planetary Science Letters 192: 485. Bibcode 2001E&PSL.192..485E. doi:10.1016/S0012-821X(01)00480-0. 
  3. ^ a b Greenwood, Norman N.; Earnshaw, A. (1984), Chemistry of the Elements, Oxford: Pergamon, pp. 1117–19, ISBN 0-08-022057-6 
  4. ^ Jamieson J, Olinger B (1969). "Pressure Temperature Studies of Anatase, Brookite, Rutile and TiO2 II: A discussion". Mineralogical Notes 54: 1477. 
  5. ^ Hanaor D, Sorrell C (2011). "Review of the anatase to rutile phase transformation". Journal of Materials Science 46: 1–20. 
  6. ^ Marchand R., Brohan L., Tournoux M. (1980). "A new form of titanium dioxide and the potassium octatitanate K2Ti8O17". Materials Research Bulletin 15 (8): 1129–1133. doi:10.1016/0025-5408(80)90076-8. 
  7. ^ Latroche, M; Brohan, L; Marchand, R; Tournoux, (1989). "New hollandite oxides: TiO2(H) and K0.06TiO2". Journal of Solid State Chemistry 81 (1): 78–82. doi:10.1016/0022-4596(89)90204-1. 
  8. ^ J. Akimoto, Y. Gotoh, Y. Oosawa, N. Nonose, T. Kumagai, K. Aoki, H. Takei (1994). "Topotactic Oxidation of Ramsdellite-Type Li0.5TiO2, a New Polymorph of Titanium Dioxide: TiO2(R)". Journal of Solid State Chemistry 113 (1): 27–36. doi:10.1006/jssc.1994.1337. 
  9. ^ P. Y. Simons, F. Dachille (1967). "The structure of TiO2II, a high-pressure phase of TiO2". Acta Crystallographica 23 (2): 334–336. doi:10.1107/S0365110X67002713. 
  10. ^ Sato H. , Endo S, Sugiyama M, Kikegawa T, Shimomura O, Kusaba K (1991). "Baddeleyite-Type High-Pressure Phase of TiO2". Science 251 (4995): 786–788. doi:10.1126/science.251.4995.786. PMID 17775458. 
  11. ^ Dubrovinskaia N A, Dubrovinsky L S., Ahuja R, Prokopenko V B., Dmitriev V., Weber H.-P., Osorio-Guillen J. M., Johansson B (2001). "Experimental and Theoretical Identification of a New High-Pressure TiO2 Polymorph.". Phys. Rev. Lett. 87 (27 Pt 1): 275501. Bibcode 2001PhRvL..87A5501D. doi:10.1103/PhysRevLett.87.275501. PMID 11800890. 
  12. ^ Mattesini M, de Almeida J. S., Dubrovinsky L., Dubrovinskaia L, Johansson B., Ahuja R. (2004). "High-pressure and high-temperature synthesis of the cubic TiO2 polymorph". Phys. Rev. B 70: 212101. doi:10.1103/PhysRevB.70.212101. 
  13. ^ Dubrovinsky, LS; Dubrovinskaia, NA; Swamy, V; Muscat, J; Harrison, NM; Ahuja, R; Holm, B; Johansson, B (2001). "Materials science: The hardest known oxide". Nature 410 (6829): 653–654. doi:10.1038/35070650. PMID 11287944. 
  14. ^ Emsley, John (2001). Nature's Building Blocks: An A–Z Guide to the Elements. Oxford: Oxford University Press. pp.  451–53. ISBN 0-19-850341-5. 
  15. ^ Banfield, J. F., Veblen, D. R., and Smith, D. J. (1991). "The identification of naturally occurring TiO2 (B) by structure determination using high-resolution electron microscopy, image simulation, and distance–least–squares refinement". American Mineralogist 76: 343. 
  16. ^ "Titanium Dioxide Manufacturing Processes". Millennium Inorganic Chemicals. Archived from the original on 2007-08-14. http://web.archive.org/web/20070814123315/http://www.millenniumchem.com/Products+and+Services/Products+by+Type/Titanium+Dioxide+-+Paint+and+Coatings/r_TiO2+Fundamentals/Titanium+Dioxide+Manufacturing+Processes_EN.htm. Retrieved 2007-09-05. 
  17. ^ Gregory Mogilevsky, Qiang Chen, Alfred Kleinhammes, Yue Wu, The structure of multilayered titania nanotubes based on delaminated anatase, Chemical Physics Letters, Volume 460, Issues 4-6, 30 July 2008, Pages 517-520, ISSN 0009-2614, DOI: 10.1016/j.cplett.2008.06.063. (http://www.sciencedirect.com/science/article/B6TFN-4SVKST5-4/2/d58f9d2dcecde18150898ff641610a1d)
  18. ^ Graham Armstrong, A. Robert Armstrong, Jesús Canales and Peter G. Bruce (2005). "Nanotubes with the TiO2-B structure". Chemical Communications (19): 2454. doi:10.1039/B501883H. PMID 15886768. http://www.rsc.org/publishing/journals/CC/article.asp?doi=b501883h. 
  19. ^ Lance G. Phillips and David M. Barbano. "The Influence of Fat Substitutes Based on Protein and Titanium Dioxide on the Sensory Properties of Lowfat Milk". Journal of Dairy Science 80 (11): 2726. http://jds.fass.org/cgi/content/abstract/80/11/2726. 
  20. ^ "Light spells doom for bacteria". http://www.photonics.com/Content/ReadArticle.aspx?ArticleID=35722. 
  21. ^ Kurtoglu, M. E., Longenbach, T. and Gogotsi, Y. (2011), Preventing Sodium Poisoning of Photocatalytic TiO2 Films on Glass by Metal Doping. International Journal of Applied Glass Science, 2: 108–116. doi: 10.1111/j.2041-1294.2011.00040.x
  22. ^ a b c "Japan Nanonet Bulletin - 44th Issue - May 12, 2005: Discovery and applications of photocatalysis —Creating a comfortable future by making use of light energy"
  23. ^ Fujishima, AKIRA; Honda, K (1972). "Electrochemical Photolysis of Water at a Semiconductor Electrode". Nature 238 (5358): 37. doi:10.1038/238037a0. PMID 12635268. 
  24. ^ "Carbon-doped titanium dioxide is an effective photocatalyst". Advanced Ceramics Report. 1 December 2003. "This carbon-doped titanium dioxide is highly efficient; under artificial visible light, it breaks down chlorophenol five times more efficiently than the nitrogen-doped version." 
  25. ^ "A Dash of Disorder Yields a Very Efficient Photocatalyst"
  26. ^ "Smog-busting paint soaks up noxious gases", Jenny Hogan, 'newscientist.com, February 4, 2004
  27. ^ TIME's Best Inventions of 2008, October 31, 2008
  28. ^ "Titanium Oxide for High-Density Data Storage". Research. http://www.redorbit.com/news/technology/1869698/new_disc_could_hold_a_thousand_times_more_data/. Retrieved May 24, 2010. 
  29. ^ Jones, BJ; Vergne, MJ; Bunk, DM; Locascio, LE; Hayes, MA (2007). "Cleavage of Peptides and Proteins Using Light-Generated Radicals from Titanium Dioxide". Anal. Chem. 79 (4): 1327–1332. doi:10.1021/ac0613737. PMID 17297930. 
  30. ^ Lewis, Nathan. "Nanocrystalline TiO2". Research. California Institute of Technology. http://nsl.caltech.edu/research.nt.html. Retrieved October 9, 2009. 
  31. ^ M. D. Earle (1942). "The Electrical Conductivity of Titanium Dioxide". Physical Review 61 (1-2): 56. doi:10.1103/PhysRev.61.56. 
  32. ^ Paschotta, Rüdiger. "Bragg Mirrors". Encyclopedia of Laser Physics and Technology. RP Photonics. http://www.rp-photonics.com/bragg_mirrors.html. Retrieved May 1, 2009. 
  33. ^ Handbook of Chemistry and Physics (89 ed.). 2008–2009. 
  34. ^ Occupational Health Services, Inc. (31 May 1988). "Hazardline" (Electronic Bulletin). New York: Occupational Health Services, Inc.. 
  35. ^ Sax, N.I.; Richard J. Lewis, Sr. (2000). Dangerous Properties of Industrial Materials. III (10th ed.). New York: Van Nostrand Reinhold. p. 3279. ISBN 978-0471354079. 
  36. ^ "Manufactured Nanomaterials and Sunscreens: Top Reasons for Precaution". August 19, 2009. http://www.foe.org/sites/default/files/SunscreensReport.pdf. Retrieved April 12, 2010. 
  37. ^ "Nano-tech sunscreen presents potential health risk". ABC News. December 18, 2008. http://www.abc.net.au/news/stories/2008/12/18/2450030.htm. Retrieved April 12, 2010. 
  38. ^ "Nano World: Nanoparticle toxicity tests". Physorg.com. April 5, 2006. http://www.physorg.com/news63466994.html. Retrieved April 12, 2010. 
  39. ^ Titanium dioxide. 93. International Agency for Research on Cancer. 2006. http://monographs.iarc.fr/ENG/Monographs/vol93/mono93.pdf. 
  40. ^ Kutal, C., Serpone, N. (1993). Photosensitive Metal Organic Systems: Mechanistic Principles and Applications. American Chemical Society, Washington D.C.
  41. ^ "Suncream may be linked to Alzheimer's disease, say experts". Daily Mail (London). 24 August 2009. http://www.dailymail.co.uk/health/article-1208720/Suncream-linked-Alzheimers-disease-say-experts.html. Retrieved 2009-08-25. 
  42. ^ "Nanoparticles Used in Common Household Items Cause Genetic Damage in Mice". 17 November 2009. http://www.sciencedaily.com/releases/2009/11/091116165739.htm. Retrieved 2009-11-17. 
  43. ^ Boffetta, P., Soutar, A., Cherrie, J.W., et al. (2004). “Mortality among workers employed in the titanium dioxide production industry in Europe.” Cancer Causes Control 15(7): 697-706; Chen, J.L., Fayerweather, W.E. (1988). “Epidemiologic study of workers exposed to titanium dioxide.” J. Occup. Med. 30(12): 937-942; Ellis, E.D., Watkins, J., Tankersley, W., et al. (2010). “Mortality Among Titanium Dioxide Workers at Three DuPont Plants.” J. Occup. Environ. Med. 52(3): 303-309; Fryzek, J.P., et al. (2003). “A cohort mortality study among titanium dioxide manufacturing workers in the United States.” J. Occup. Environ. Med. 45(4): 400-409; and Ramanakumar, A.V., et al. (2008). “Risk of lung cancer following exposure to carbon black, titanium dioxide and talc: Results from two case-control studies in Montreal.” Int. J. Cancer 122: 183-189.

[edit] External links

v · d · eSunscreening agents approved by the US FDA or other agencies
UVA: 400–315 nm • UVB: 315–290 nm • chemical agents unless otherwise noted
UVA filters
UVB filters
UVA+UVB filters

Retrieved from "http://en.wikipedia.org/wiki/Titanium_dioxide"
Personal tools
Namespaces
Variants
Actions
Navigation
Interaction
Toolbox
Print/export
Languages