Titanium dioxide

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Titanium dioxide
Rutile-unit-cell-3D-balls.png
Unit cell of titanium dioxide (rutile form)
  Titanium   Oxygen
Titanium(IV) oxide.jpg
Names
IUPAC names
Titanium dioxide
Titanium(IV) oxide
Other names
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.033.327 OOjs UI icon edit-ltr-progressive.svg
E number E171 (colours)
KEGG
PubChem CID
RTECS number
  • XR2775000
UNII
  • InChI=1S/2O.Ti Yes check.svgY
    Key: GWEVSGVZZGPLCZ-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/2O.Ti/rO2Ti/c1-3-2
    Key: GWEVSGVZZGPLCZ-TYTSCOISAW
  • O=[Ti]=O
Properties
TiO
2
Molar mass 79.866 g/mol
AppearanceWhite solid
Odor Odorless
Density
  • 4.23 g/cm3 (rutile)
  • 3.78 g/cm3 (anatase)
Melting point 1,843 °C (3,349 °F; 2,116 K)
Boiling point 2,972 °C (5,382 °F; 3,245 K)
Insoluble
Band gap 3.21 eV (anatase) [1]

3.15 eV (rutile) [1]

+5.9·10−6 cm3/mol
  • 2.488 (anatase)
  • 2.583 (brookite)
  • 2.609 (rutile)
Thermochemistry
Std molar
entropy (S⦵298)
50 J·mol−1·K−1 [2]
−945 kJ·mol−1 [2]
Hazards
NFPA 704 (fire diamond)
NFPA 704.svgHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
0
0
Flash point not flammable
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 15 mg/m3 [3]
REL (Recommended)
Ca [3]
IDLH (Immediate danger)
Ca [5000 mg/m3] [3]
Safety data sheet (SDS) ICSC 0338
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
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Titanium dioxide, also known as titanium(IV) oxide or titania /taɪˈteɪniə/ , is the inorganic compound derived from titanium with the chemical formula TiO
2. When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891 . [4] It is a white solid that is insoluble in water, although mineral forms can appear black. As a pigment, 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 tonnes. [5] [6] [7] It has been estimated that titanium dioxide is used in two-thirds of all pigments, and pigments based on the oxide have been valued at a price of $13.2 billion. [8]

Structure

In all three of its main dioxides, titanium exhibits octahedral geometry, being bonded to six oxide anions. The oxides in turn are bonded to three Ti centers. The overall crystal structures of rutile and anatase are tetragonal in symmetry whereas brookite is orthorhombic. The oxygen substructures are all slight distortions of close packing: in rutile, the oxide anions are arranged in distorted hexagonal close-packing, whereas they are close to cubic close-packing in anatase and to "double hexagonal close-packing" for brookite. The rutile structure is widespread for other metal dioxides and difluorides, e.g. RuO2 and ZnF2.

Molten titanium dioxide has a local structure in which each Ti is coordinated to, on average, about 5 oxygen atoms. [9] This is distinct from the crystalline forms in which Ti coordinates to 6 oxygen atoms.

Structure of anatase. Together with rutile and brookite, one of the three major polymorphs of TiO2. Anatase crystal structure.png
Structure of anatase. Together with rutile and brookite, one of the three major polymorphs of TiO2.

Synthetic and geologic occurrence

Synthetic TiO2 is mainly produced from the mineral ilmenite. Rutile, and anatase, naturally occurring TiO2, occur widely also, e.g. rutile as a 'heavy mineral' in beach sand. Leucoxene, fine-grained anatase formed by natural alteration of ilmenite, is yet another ore. Star sapphires and rubies get their asterism from oriented inclusions of rutile needles. [10]

Mineralogy and uncommon polymorphs

Titanium dioxide occurs in nature as the minerals rutile and anatase. Additionally two high-pressure forms are known minerals: a monoclinic baddeleyite-like form known as akaogiite, and the other has a slight monoclinic distortion of the orthorhombic α-PbO2 structure and is known as riesite. Both of which can be found at the Ries crater in Bavaria. [11] [12] [13] It is mainly sourced from ilmenite, which is the most widespread 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 (1,110–1,470 °F). [14]

Titanium dioxide has twelve known polymorphs – in addition to rutile, anatase, brookite, akaogiite and riesite, three metastable phases can be produced synthetically (monoclinic, tetragonal, and orthorhombic ramsdellite-like), and four high-pressure forms (α-PbO2-like, cotunnite-like, orthorhombic OI, and cubic phases) also exist:

FormCrystal systemSynthesis
Rutile Tetragonal
Anatase Tetragonal
Brookite Orthorhombic
TiO2(B) [15] Monoclinic Hydrolysis of K2Ti4O9 followed by heating
TiO2(H), hollandite-like form [16] Tetragonal Oxidation of the related potassium titanate bronze, K0.25TiO2
TiO2(R), ramsdellite-like form [17] Orthorhombic Oxidation of the related lithium titanate bronze Li0.5TiO2
TiO2(II)-(α-PbO2-like form) [18] Orthorhombic
Akaogiite (baddeleyite-like form, 7 coordinated Ti) [19] Monoclinic
TiO2 -OI [20] Orthorhombic
Cubic form [21] Cubic P > 40 GPa, T > 1600 °C
TiO2 -OII, cotunnite(PbCl2)-like [22] Orthorhombic P > 40 GPa, T > 700 °C

The cotunnite-type phase was claimed 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. [22] 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) [23] and bulk modulus (~300 GPa). [24] [25]

Titanium dioxide (B) is found as a mineral in magmatic rocks and hydrothermal veins, as well as weathering rims on perovskite. TiO2 also forms lamellae in other minerals. [26]

Production

Industrial key players in the production of titanium dioxide - 2022 Industrial key players in the production of titanium dioxide.png
Industrial key players in the production of titanium dioxide - 2022

The largest TiO
2 pigment processors are Chemours, Venator, Kronos  [ de ], and Tronox. [27] [28] Major paint and coating company end users for pigment grade titanium dioxide include Akzo Nobel, PPG Industries, Sherwin Williams, BASF, Kansai Paints and Valspar. [29] Global TiO
2 pigment demand for 2010 was 5.3 Mt with annual growth expected to be about 3–4%. [30]

Evolution of the global production of titanium dioxide according to process Evolution production dioxyde de titane.svg
Evolution of the global production of titanium dioxide according to process

The production method depends on the feedstock. In addition to ores, other feedstocks include upgraded slag. Both the chloride process and the sulfate process (both described below) produce titanium dioxide pigment in the rutile crystal form, but the sulfate process can be adjusted to produce the anatase form. Anatase, being softer, is used in fiber and paper applications. The sulfate process is run as a batch process; the chloride process is run as a continuous process. [31]

Chloride process

In chloride process, the ore is treated with chlorine and carbon to give titanium tetrachloride, a volatile liquid that is further purified by distillation. The TiCl4 is treated with oxygen to regenerate chlorine and produce the titanium dioxide.

Sulfate process

In the sulfate process, ilmenite is treated with sulfuric acid to extract iron(II) sulfate pentahydrate. This process requires concentrated ilmenite (45–60% TiO2) or pretreated feedstocks as a suitable source of titanium. [32] The resulting synthetic rutile is further processed according to the specifications of the end user, i.e. pigment grade or otherwise. [33]

Examples of plants using the sulfate process are the Sorel-Tracy plant of QIT-Fer et Titane and the Eramet Titanium & Iron smelter in Tyssedal Norway. [34]

Becher process

The Becher process is another method for the production of synthetic rutile from ilmenite. It first oxidizes the ilmenite as a means to separate the iron component.

Specialized methods

For specialty applications, TiO2 films are prepared by various specialized chemistries. [35] Sol-gel routes involve the hydrolysis of titanium alkoxides such as titanium ethoxide:

Ti(OEt)4 + 2 H2O → TiO2 + 4 EtOH

A related approach that also relies on molecular precursors involves chemical vapor deposition. In this method, the alkoxide is volatilized and then decomposed on contact with a hot surface:

Ti(OEt)4 → TiO2 + 2 Et2O

Applications

Pigment

First mass-produced in 1916, [36] titanium dioxide is the most widely used white pigment because of its brightness and very high refractive index, in which it is surpassed only by a few other materials (see list of indices of refraction ). Titanium dioxide crystal size is ideally around 220 nm (measured by electron microscope) to optimize the maximum reflection of visible light. However, abnormal grain growth is often observed in titanium dioxide, particularly in its rutile phase. [37] The occurrence of abnormal grain growth brings about a deviation of a small number of crystallites from the mean crystal size and modifies the physical behaviour of TiO2. The optical properties of the finished pigment are highly sensitive to purity. As little as a few parts per million (ppm) of certain metals (Cr, V, Cu, Fe, Nb) can disturb the crystal lattice so much that the effect can be detected in quality control. [38] Approximately 4.6 million tons of pigmentary TiO2 are used annually worldwide, and this number is expected to increase as use continues to rise. [39]

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, supplements, medicines (i.e. pills and tablets), and most toothpastes; in 2019 it was present in two-thirds of toothpastes on the French market. [40] In paint, it is often referred to offhandedly as "brilliant white", "the perfect white", "the whitest white", or other similar terms. Opacity is improved by optimal sizing of the titanium dioxide particles.

Food additive

In food, it is commonly found in ice creams, chocolates, all types of candy, creamers, desserts, marshmallows, chewing gum, pastries, spreads, dressings, cakes, some cheeses, and many other foods. [41]

Thin films

When deposited as a thin film, its refractive index and colour make it an excellent reflective optical coating for dielectric mirrors; it is also used in generating decorative thin films such as found in "mystic fire topaz".

Some grades of modified titanium based pigments as used in sparkly paints, plastics, finishes and cosmetics – these are man-made pigments whose particles have two or more layers of various oxides – often titanium dioxide, iron oxide or alumina – in order to have glittering, iridescent and or pearlescent effects similar to crushed mica or guanine-based products. In addition to these effects a limited colour change is possible in certain formulations depending on how and at which angle the finished product is illuminated and the thickness of the oxide layer in the pigment particle; one or more colours appear by reflection while the other tones appear due to interference of the transparent titanium dioxide layers. [42] In some products, the layer of titanium dioxide is grown in conjunction with iron oxide by calcination of titanium salts (sulfates, chlorates) around 800 °C [43] One example of a pearlescent pigment is Iriodin, based on mica coated with titanium dioxide or iron (III) oxide. [44]

The iridescent effect in these titanium oxide particles is unlike the opaque effect obtained with usual ground titanium oxide pigment obtained by mining, in which case only a certain diameter of the particle is considered and the effect is due only to scattering.

Sunscreen and UV blocking pigments

In cosmetic and skin care products, titanium dioxide is used as a pigment, sunscreen and a thickener. As a sunscreen, ultrafine TiO2 is used, which is notable in that combined with ultrafine zinc oxide, it is considered to be an effective sunscreen that lowers the incidence of sun burns and minimizes the premature photoaging, photocarcinogenesis and immunosuppression associated with long term excess sun exposure. [45] Sometimes these UV blockers are combined with iron oxide pigments in sunscreen to increase visible light protection. [46]

Titanium dioxide and zinc oxide are generally considered to be less harmful to coral reefs than sunscreens that include chemicals such as oxybenzone, octocrylene and octinoxate. [47]

Nanosized titanium dioxide is found in the majority of physical sunscreens because of 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. Nano-scaled (particle size of 20–40 nm) [48] titanium dioxide particles are primarily used in sunscreen lotion because they scatter visible light much less than titanium dioxide pigments, and can give UV protection. [39] 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. Nano-TiO2, which blocks both UV-A and UV-B radiation, is used in sunscreens and other cosmetic products.

The EU Scientific Committee on Consumer Safety considered nano sized titanium dioxide to be safe for skin applications, in concentrations of up to 25 percent based on animal testing. [49] The risk assessment of different titanium dioxide nanomaterials in sunscreen is currently evolving since nano-sized TiO2 is different from the well-known micronized form. [50] The rutile form is generally used in cosmetic and sunscreen products due to it not possessing any observed ability to damage the skin under normal conditions [51] and having a higher UV absorption. [52] In 2016 Scientific Committee on Consumer Safety (SCCS) tests concluded that the use of nano titanium dioxide (95–100% rutile, ≦5% anatase) as a UV filter can be considered to not pose any risk of adverse effects in humans post-application on healthy skin, [53] except in the case the application method would lead to substantial risk of inhalation (ie; powder or spray formulations). This safety opinion applied to nano TiO2 in concentrations of up to 25%. [54]

Initial studies indicated that nano-TiO2 particles could penetrate the skin, causing concern over its use. These studies were later refuted, when it was discovered that the testing methodology couldn't differentiate between penetrated particles and particles simply trapped in hair follicles and that having a diseased or physically damaged dermis could be the true cause of insufficient barrier protection. [50]

SCCS research found that when nanoparticles had certain photostable coatings (e.g., alumina, silica, cetyl phosphate, triethoxycaprylylsilane, manganese dioxide), the photocatalytic activity was attenuated and no notable skin penetration was observed; the sunscreen in this research was applied at amounts of 10 mg/cm2 for exposure periods of 24 hours. [54] Coating TiO2 with alumina, silica, zircon or various polymers can minimize avobenzone degradation [55] and enhance UV absorption by adding an additional light diffraction mechanism. [52]

TiO
2 is used extensively in plastics and other applications as a white pigment or an opacifier and for its UV resistant properties where the powder disperses light – unlike organic UV absorbers – and reduces UV damage, due mostly to the particle's high refractive index. [56]

Other uses of titanium dioxide

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

It is used as a tattoo pigment and in styptic pencils. Titanium dioxide is produced in varying particle sizes which are both oil and water dispersible, and in certain grades for the cosmetic industry. It is also a common ingredient in toothpaste.

The exterior of the Saturn V rocket was painted with titanium dioxide; this later allowed astronomers to determine that J002E3 was likely the S-IVB stage from Apollo 12 and not an asteroid. [57]

Titanium dioxide is an n-type semiconductor and is used in dye-sensitized solar cells. [58] It is also used in other electronics components such as electrodes in batteries. [59]

Research

Patenting activities

Relevant patent families describing titanium dioxide production from ilmenite, 2002-2021. Relevant patent families describing titanium dioxide production from ilmenite, 2002-2021.png
Relevant patent families describing titanium dioxide production from ilmenite, 2002–2021.
Academic and public institutions having significant patent activity in titanium dioxide production, 2022. Public Institutions patent activity in titanium dioxide production.png
Academic and public institutions having significant patent activity in titanium dioxide production, 2022.

Between 2002 and 2022, there were 459 patent families that describe the production of titanium dioxide from ilmenite. The majority of these patents describe pre-treatment processes, such as using smelting and magnetic separation to increase titanium concentration in low-grade ores, leading to titanium concentrates or slags. Other patents describe processes to obtain titanium dioxide, either by a direct hydrometallurgical process or through the main industrial production processes, the sulfate process and the chloride process. [60] The sulfate process represents 40% of the world’s titanium dioxide production and is protected in 23% of patent families. The chloride process is only mentioned in 8% of patent families, although it provides 60% of the worldwide industrial production of titanium dioxide. [60]

Key contributors to patents on the production of titanium dioxide are companies from China, Australia and the United States, reflecting the major contribution of these countries to industrial production. Chinese companies Pangang and Lomon Billions Groups hold major patent portfolios. [60]

Photocatalyst

Nanosized titanium dioxide, particularly in the anatase form, exhibits photocatalytic activity under ultraviolet (UV) irradiation. This photoactivity is reportedly most pronounced at the {001} planes of anatase, [61] [62] although the {101} planes are thermodynamically more stable and thus more prominent in most synthesised and natural anatase, [63] as evident by the often observed tetragonal dipyramidal growth habit. Interfaces between rutile and anatase are further considered to improve photocatalytic activity by facilitating charge carrier separation and as a result, biphasic titanium dioxide is often considered to possess enhanced functionality as a photocatalyst. [64] It has been reported that titanium dioxide, when doped with nitrogen ions or doped with metal oxide like tungsten trioxide, exhibits excitation also under visible light. [65] The strong oxidative potential of the positive holes oxidizes water to create hydroxyl radicals. It can also oxidize oxygen or organic materials directly. Hence, in addition to its use as a pigment, titanium dioxide can be 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 nanosized titanium dioxide were discovered by Akira Fujishima in 1967 [66] and published in 1972. [67] The process on the surface of the titanium dioxide was called the Honda-Fujishima effect  [ ja ]. [66] In thin film and nanoparticle form, titanium dioxide has the potential for use in energy production: As a photocatalyst, it can break water into hydrogen and oxygen. With 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. [68] Further efficiency and durability has been obtained by introducing disorder to the lattice structure of the surface layer of titanium dioxide nanocrystals, permitting infrared absorption. [69] Visible-light-active nanosized anatase and rutile has been developed for photocatalytic applications. [70] [71]

In 1995 Fujishima and his group discovered the superhydrophilicity phenomenon for titanium dioxide coated glass exposed to sun light. [66] This resulted in the development of self-cleaning glass and anti-fogging coatings.

Nanosized TiO2 incorporated into outdoor building materials, such as paving stones in noxer blocks [72] or paints, could reduce concentrations of airborne pollutants such as volatile organic compounds and nitrogen oxides. [73] A TiO2-containing cement has been produced. [74]

Using TiO2 as a photocatalyst, attempts have been made to mineralize pollutants (to convert into CO2 and H2O) in waste water. [75] [76] [77] The photocatalytic destruction of organic matter could also be exploited in coatings with antimicrobial applications. [78]

Hydroxyl radical formation

Although nanosized anatase TiO2 does not absorb visible light, it does strongly absorb ultraviolet (UV) radiation (hv), leading to the formation of hydroxyl radicals. [79] This occurs when photo-induced valence bond holes (h+vb) are trapped at the surface of TiO2 leading to the formation of trapped holes (h+tr) that cannot oxidize water. [80]

TiO2 + hv → e− + h+vb
h+vb → h+tr
O2 + e− → O2•−
O2•− + O2•−+ 2  H+ → H2O2 + O2
O2•− + h+vb → O2
O2•− + h+tr → O2
  OH− + h+vb → HO•
e− + h+tr → recombination
Note: Wavelength (λ)= 387 nm [80] This reaction has been found to mineralize and decompose undesirable compounds in the environment, specifically the air and in wastewater. [80]
Synthetic single crystals of TiO2, ca. 2-3 mm in size, cut from a larger plate TiO2crystals.JPG
Synthetic single crystals of TiO2, ca. 2–3 mm in size, cut from a larger plate

Nanotubes

Titanium oxide nanotubes, SEM image TiO2nanotube.jpg
Titanium oxide nanotubes, SEM image
Nanotubes of titanium dioxide (TiO2-Nt) obtained by electrochemical synthesis. The SEM image shows an array of vertical self-ordered TiO2-Nt with closed bottom ends of tubes. The army of titanium dioxide nanotubes.jpg
Nanotubes of titanium dioxide (TiO2-Nt) obtained by electrochemical synthesis. The SEM image shows an array of vertical self-ordered TiO2-Nt with closed bottom ends of tubes.

Anatase can be converted into non-carbon nanotubes and nanowires. [81] Hollow TiO2 nanofibers can be also prepared by coating carbon nanofibers by first applying titanium butoxide. [82]

Solubility

Titanium dioxide is insoluble in water, organic solvents, and inorganic acids. It is slightly soluble in alkali, soluble in saturated potassium acid carbonate, and can be completely dissolved in strong sulfuric acid and hydrofluoric acid after boiling for a long time. [83]

SEM (top) and TEM (bottom) images of chiral TiO2 nanofibers Chiral TiO2 nanofibers 2.jpg
SEM (top) and TEM (bottom) images of chiral TiO2 nanofibers

Health and safety

Widely-occurring minerals and even gemstones are composed of TiO2. All natural titanium, comprising more than 0.5% of the Earth's crust, exists as oxides. [84]

Food additive

As of 2006, titanium dioxide had been regarded as "completely nontoxic when orally administered". [4] However, concerns persist.

Government policies

TiO2 whitener in food was banned in France from 2020, due to uncertainty about safe quantities for human consumption. [85]

In 2021, the European Food Safety Authority (EFSA) ruled that as a consequence of new understandings of nanoparticles, titanium dioxide could "no longer be considered safe as a food additive", and the EU health commissioner announced plans to ban its use across the EU, with discussions beginning in June 2021. EFSA concluded that genotoxicity—which could lead to carcinogenic effects—could not be ruled out, and that a "safe level for daily intake of the food additive could not be established". [86] In 2022, the UK Food Standards Agency and Food Standards Scotland announced their disagreement with the EFSA ruling, and did not follow the EU in banning titanium dioxide as a food additive. [87] Health Canada similarly reviewed the available evidence in 2022 and decided not to change their position on titanium dioxide as a food additive. [88]

The European Union removed the authorization to use titanium dioxide (E 171) in foods, effective 7 February 2022, with a six months grace period. [89]

As of May 2023, following the European Union 2022 ban, the U.S. states California and New York were considering banning the use of titanium dioxide in foods. [90]

As of 2024, the Food and Drug Administration (FDA) in the United States permits titanium dioxide as a food additive. It may be used to increase whiteness and opacity in dairy products (some cheeses, ice cream, and yogurt), candies, frostings, fillings, and many other foods. The FDA regulates the labeling of products containing titanium dioxide, alllowing the product's ingredients list to identify titanium dioxide either as "color added" or "artificial colors" or "titanium dioxide;" it does not require that titanium dioxide be explicitly named [91] [92] [93] despite growing scientific concerns. [94] In 2023, the Consumer Healthcare Products Association, a manufacturer's trade group, defended the substance as safe at certain limits while allowing that additional studies could provide further insight, saying an immediate ban would be a "knee-jerk" reaction. [95]

Industry response

Dunkin' Donuts dropped titanium dioxide from their merchandise in 2015 after public pressure. [96]

Research as an ingestible nanomaterial

Due to the potential that long-term ingestion of titanium dioxide may be toxic, particularly to cells and functions of the gastrointestinal tract, preliminary research as of 2021 was assessing its possible role in disease development, such as inflammatory bowel disease and colorectal cancer. [97]

Size distribution analyses showed that batches of food-grade TiO₂, which is produced with a target particle size in the 200–300 nm range for optimal pigmentation qualities, always include a nanoparticle-sized fraction as inevitable byproduct of the manufacturing processes. [98]

Andrew Maynard, director of Risk Science Center at the University of Michigan, rejected the supposed danger from use of titanium dioxide in food. He says that the titanium dioxide used by Dunkin' Brands and many other food producers is not a new material, and it is not a nanomaterial either. Nanoparticles are typically smaller than 100 nanometres in diameter, yet most of the particles in food-grade titanium dioxide are much larger. [99]

Inhalation

Titanium dioxide dust, when inhaled, has been classified by the International Agency for Research on Cancer (IARC) as an IARC Group 2B carcinogen, meaning it is possibly carcinogenic to humans. [100] [101] The US National Institute for Occupational Safety and Health recommends two separate exposure limits. NIOSH recommends that fine TiO
2 particles be set at an exposure limit of 2.4 mg/m3, while ultrafine TiO
2 be set at an exposure limit of 0.3 mg/m3, as time-weighted average concentrations up to 10 hours a day for a 40-hour work week. [102]

Although no evidence points to acute toxicity, recurring concerns have been expressed about nanophase forms of these materials. Studies of workers with high exposure to TiO2 particles indicate that even at high exposure there is no adverse effect to human health. [84]

Environmental waste introduction

Titanium dioxide (TiO₂) is mostly introduced into the environment as nanoparticles via wastewater treatment plants. [103] Cosmetic pigments including titanium dioxide enter the wastewater when the product is washed off into sinks after cosmetic use. Once in the sewage treatment plants, pigments separate into sewage sludge which can then be released into the soil when injected into the soil or distributed on its surface. 99% of these nanoparticles wind up on land rather than in aquatic environments due to their retention in sewage sludge. [103] In the environment, titanium dioxide nanoparticles have low to negligible solubility and have been shown to be stable once particle aggregates are formed in soil and water surroundings. [103] In the process of dissolution, water-soluble ions typically dissociate from the nanoparticle into solution when thermodynamically unstable. TiO2 dissolution increases when there are higher levels of dissolved organic matter and clay in the soil. However, aggregation is promoted by pH at the isoelectric point of TiO2 (pH= 5.8) which renders it neutral and solution ion concentrations above 4.5 mM. [104] [105]

See also

Sources

Definition of Free Cultural Works logo notext.svg  This article incorporates text from a free content work.Licensed under CC-BY.Text taken from Production of titanium and titanium dioxide from ilmenite and related applications​ ,WIPO.

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<span class="mw-page-title-main">Titanium</span> Chemical element with atomic number 22 (Ti)

Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in sea water, aqua regia, and chlorine.

<span class="mw-page-title-main">Rutile</span> Oxide mineral composed of titanium dioxide

Rutile is an oxide mineral composed of titanium dioxide (TiO2), the most common natural form of TiO2. Rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite.

<span class="mw-page-title-main">Anatase</span> Mineral form of titanium dioxide

Anatase is a metastable mineral form of titanium dioxide (TiO2) with a tetragonal crystal structure. Although colorless or white when pure, anatase in nature is usually a black solid due to impurities. Three other polymorphs (or mineral forms) of titanium dioxide are known to occur naturally: brookite, akaogiite, and rutile, with rutile being the most common and most stable of the bunch. Anatase is formed at relatively low temperatures and found in minor concentrations in igneous and metamorphic rocks. Glass coated with a thin film of TiO2 shows antifogging and self-cleaning properties under ultraviolet radiation.

<span class="mw-page-title-main">Ilmenite</span> Titanium-iron oxide mineral

Ilmenite is a titanium-iron oxide mineral with the idealized formula FeTiO
3. It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printing inks, fabrics, plastics, paper, sunscreen, food and cosmetics.

<span class="mw-page-title-main">Zirconium dioxide</span> Chemical compound

Zirconium dioxide, sometimes known as zirconia, is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the mineral baddeleyite. A dopant stabilized cubic structured zirconia, cubic zirconia, is synthesized in various colours for use as a gemstone and a diamond simulant.

<span class="mw-page-title-main">Brookite</span>

Brookite is the orthorhombic variant of titanium dioxide (TiO2), which occurs in four known natural polymorphic forms (minerals with the same composition but different structure). The other three of these forms are akaogiite (monoclinic), anatase (tetragonal) and rutile (tetragonal). Brookite is rare compared to anatase and rutile and, like these forms, it exhibits photocatalytic activity. Brookite also has a larger cell volume than either anatase or rutile, with 8 TiO2 groups per unit cell, compared with 4 for anatase and 2 for rutile. Iron (Fe), tantalum (Ta) and niobium (Nb) are common impurities in brookite.

<span class="mw-page-title-main">Zinc oxide</span> White powder insoluble in water

Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder which is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceramics, glass, cement, lubricants, paints, sunscreens, ointments, adhesives, sealants, pigments, foods, batteries, ferrites, fire retardants, semi conductors, and first-aid tapes. Although it occurs naturally as the mineral zincite, most zinc oxide is produced synthetically.

<span class="mw-page-title-main">Opacifier</span>

An opacifier is a substance added to a material in order to make the ensuing system opaque. An example of a chemical opacifier is titanium dioxide (TiO2), which is used as an opacifier in paints, in paper, and in plastics. It has very high refraction index (rutile modification 2.7 and anatase modification 2.55) and optimum refraction is obtained with crystals about 225 nanometers. Impurities in the crystal alter the optical properties. It is also used to opacify ceramic glazes and milk glass; bone ash is also used.

<span class="mw-page-title-main">Photocatalysis</span> Acceleration of a photoreaction in the presence of a catalyst

In chemistry, photocatalysis is the acceleration of a photoreaction in the presence of a photocatalyst, the excited state of which "repeatedly interacts with the reaction partners forming reaction intermediates and regenerates itself after each cycle of such interactions." In many cases, the catalyst is a solid that upon irradiation with UV- or visible light generates electron–hole pairs that generate free radicals. Photocatalysts belong to three main groups; heterogeneous, homogeneous, and plasmonic antenna-reactor catalysts. The use of each catalysts depends on the preferred application and required catalysis reaction.

The Tiwest Joint Venture was a joint venture between Tronox Western Australia Pty Ltd and subsidiaries of Exxaro Australia Sands Pty Ltd. The Tiwest Joint Venture was a mining and processing company, established in 1988, to extract ilmenite, rutile, leucoxene and zircon from a mineral sands deposit at Cooljarloo, 14 km north of Cataby, Western Australia. As of June 2012, the joint venture was formally dissolved, when Tronox acquired the mineral-sands-related divisions of Exxaro outright.

As the world's energy demand continues to grow, the development of more efficient and sustainable technologies for generating and storing energy is becoming increasingly important. According to Dr. Wade Adams from Rice University, energy will be the most pressing problem facing humanity in the next 50 years and nanotechnology has potential to solve this issue. Nanotechnology, a relatively new field of science and engineering, has shown promise to have a significant impact on the energy industry. Nanotechnology is defined as any technology that contains particles with one dimension under 100 nanometers in length. For scale, a single virus particle is about 100 nanometers wide.

Self-cleaning glass is a specific type of glass with a surface that keeps itself free of dirt and grime.

The chloride process is used to separate titanium from its ores. The goal of the process is to win high purity titanium dioxide from ores such as ilmenite (FeTiO3) and rutile (TiO2). The strategy exploits the volatility of TiCl4, which is readily purified and converted to the dioxide. Millions of tons of TiO2 are produced annually by this process, mainly for use as white pigments. The chloride process has largely displaced the older sulfate process, which relies on hot sulfuric acid to extract iron and other impurities from ores.

The Becher process is a process to produce rutile, a form of titanium dioxide, from the ore ilmenite. Although it is competitive with the chloride process and the sulfate process, . the Becher process is not used on scale.

An antimicrobial surface is coated by an antimicrobial agent that inhibits the ability of microorganisms to grow on the surface of a material. Such surfaces are becoming more widely investigated for possible use in various settings including clinics, industry, and even the home. The most common and most important use of antimicrobial coatings has been in the healthcare setting for sterilization of medical devices to prevent hospital-associated infections, which have accounted for almost 100,000 deaths in the United States. In addition to medical devices, linens and clothing can provide a suitable environment for many bacteria, fungi, and viruses to grow when in contact with the human body which allows for the transmission of infectious disease.

Nanoremediation is the use of nanoparticles for environmental remediation. It is being explored to treat ground water, wastewater, soil, sediment, or other contaminated environmental materials. Nanoremediation is an emerging industry; by 2009, nanoremediation technologies had been documented in at least 44 cleanup sites around the world, predominantly in the United States. In Europe, nanoremediation is being investigated by the EC funded NanoRem Project. A report produced by the NanoRem consortium has identified around 70 nanoremediation projects worldwide at pilot or full scale. During nanoremediation, a nanoparticle agent must be brought into contact with the target contaminant under conditions that allow a detoxifying or immobilizing reaction. This process typically involves a pump-and-treat process or in situ application.

<span class="mw-page-title-main">Nelsonite</span> Igneous rock

Nelsonite is an igneous rock primarily constituted of ilmenite and apatite, with anatase, chlorite, phosphosiderite, talc and/or wavellite appearing as minor components. Rocks are equigranular with a grain size around 2 – 3 mm. The black ilmenite is slightly magnetic while the whitish apatite is not.

<span class="mw-page-title-main">Titanium dioxide nanoparticle</span> Nanomaterial

Titanium dioxide nanoparticles, also called ultrafine titanium dioxide or nanocrystalline titanium dioxide or microcrystalline titanium dioxide, are particles of titanium dioxide with diameters less than 100 nm. Ultrafine TiO2 is used in sunscreens due to its ability to block ultraviolet radiation while remaining transparent on the skin. It is in rutile crystal structure and coated with silica or/and alumina to prevent photocatalytic phenomena. The health risks of ultrafine TiO2 from dermal exposure on intact skin are considered extremely low, and it is considered safer than other substances used for ultraviolet protection.

Nanomaterials are materials with a size ranging from 1 to 100 nm in at least one dimension. At the nanoscale, material properties become different. These unique properties can be exploited for a variety of applications, including the use of nanoparticles in skincare and cosmetics products.

The +4 oxidation state dominates titanium chemistry, but compounds in the +3 oxidation state are also numerous. Commonly, titanium adopts an octahedral coordination geometry in its complexes, but tetrahedral TiCl4 is a notable exception. Because of its high oxidation state, titanium(IV) compounds exhibit a high degree of covalent bonding.

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