TITANIUM DIOXIDE ANATASE A1

TITANIUM DIOXIDE ANATASE A1 

CAS: 13463-67-7

TITANIUM DIOXIDE; Titania; Titanium (IV) oxide; Dioxotitanium; Anatase; Rutile; TITANIUM DIOXIDE; TITANIUM DIOXIDE; titanium dioxide; titanium dioxide; titanium dioxide; titaniumdioxide; TITANIUMDIOXIDE; TITANIUM DIOXIDE; Titanium dioxide; Titaniumdioxide; UNITANE; PIGMENT WHITE 6; TIO2; TITANIC ANHYDRIDE; TITAN DIOXIDE; TITANIA; TITANIUM (+4) OXIDE; TITANIUM DIOXIDE, ANATASE; anatase (TiO2), anatase titanium dioxide, TiO2, titanium dioxide, TiO2, titanium dioxide, titan white, titandioxid, tioxide, anatase: brookite; titanium (IV) dioxide; titanic anhydride; titanic acid anhydride; titanium white; CAS # 12137-20-1 titanium monoxide (TiO), CAS # 1317-70-0 titanium dioxide (TiO2) (anatase grade), CAS # 13463-67-7 titanium (IV) oxide (titania) octahedrite; unitane; titanium dioxide P25, fumed, anatase; atlas white titanium dioxide; bayertitan; bytetan; calcotone white t; thiofine; tiona; tiona td; hombitan; kronos titanium dioxide; levanox white rkb; runa rh20; thiofine; titania; tionat.d .; tipaque; titafrance; titanox; titanox 2010; zopaque; cosmetic white C47-9623; horse head a-410; horse head a-420; horse head r-710; unitane o-110; unitane o-220; unitane or-150; unitane or-340; unitane or-342; unitane or-350; unitane or-540; unitane or-640; C.I. 77891; C.I. pigment white 6; cosmetic white C47-5175; 1700 white; a-elephant cream; austiox; bayeritian; flamenco; kronos; KH360; rayox; rutiox cr; ti-pure; titanium peroxide; titan white; trioxide (s); tronox; thioxide rhd; kronos cl 220; tioxide rsm; titanox ranc; austiox r-cr 3; R 680; RO 2; ti-pure r 900; thioxide ad-m; tioxide r.xl; cab-o-ti; ti-pure r 901; tipaque r 820; kronos rn 56; kronos rn 40p; bayertitan a; bayertitan r-u-f; thioxide r-cr; p25 (oxide); unitane or 650; unitane or 450; zopaque ldc; runa arh 20; runa arh 200; hombitan r 101d; hombitan r 610k; kronos 2073; unitane or 572; ti-pure r 101; ti-pure r 915; aerolyst 7710; anatase (TiO2); aquaspersabil R TiO2; bayertitan AN3; biogenic titania-100; ci77891; ci77891; CIpigment white 6; coverleaf MF; dioxotitanium; hallbrite T-97; kalixide CT (Vevy) ; kronos 2073; MT-01; MT-05; MT-100AQ; MT-100SA; MT-100SAS; MT-100TV; MT-100WP; MT-150W; MT-500B; MT-500H; oleosperse R TiO2; oleosperse TiO2 ; optisol OT50; optisol OTP1; photolite LY-S; photolite PK-S; siclone TD-150; titanium (IV) dioxide; titanium (IV) oxide; titanium dioxide FCC; titanium dioxide microfine dispersion in C12-15 alkyl benzoate 48.5; titanium dioxide microfinedispersion in caprylic-capric triglyderide 48.5; titanium dioxide microfine dispersion in octyl palmitate 48.5; titanium dioxide tech grade; titanium dioxide USP FCC hombitan AFDC; titanium oxide; titanium white; titanium (IV) oxide; titanium, dioxo-; trishield TS -510; unitane 0-110; uniwhite AO; titanium anats A1, titanium dioxide, titanium dioxide, titanium dioxide, titanium doxide, rutile, rutile, anatase, anatase, antase, TITANIUM DIOXIDE; Titania; Titanium (IV) oxide; Dioxotitanium; Anatase; Rutile; TITANIUM DIOXIDE; TITANIUM DIOXIDE; titanium dioxide; titanium dioxide; titanium dioxide; titaniumdioxide; TITANIUMDIOXIDE; TITANIUM DIOXIDE; Titanium dioxide; Titaniumdioxide; UNITANE; PIGMENT WHITE 6; TIO2; TITANIC ANHYDRIDE; TITAN DIOXIDE; TITANIA; TITANIUM (+4) OXIDE; TITANIUM DIOXIDE, ANATASE; anatase (TiO2), anatase titanium dioxide, TiO2, titanium dioxide, TiO2, titanium dioxide, titan white, titandioxid, tioxide, anatase: brookite; titanium (IV) dioxide; titanic anhydride; titanic acid anhydride; titanium white; CAS # 12137-20-1 titanium monoxide (TiO), CAS # 1317-70-0 titanium dioxide (TiO2) (anatase grade), CAS # 13463-67-7 titanium (IV) oxide (titania) octahedrite; unitane; titanium dioxide P25, fumed, anatase; atlas white titanium dioxide; bayertitan; bytetan; calcotone white t; thiofine; tiona; tiona td; hombitan; kronos titanium dioxide; levanox white rkb; runa rh20; thiofine; titania; tionat.d .; tipaque; titafrance; titanox; titanox 2010; zopaque; cosmetic white C47-9623; horse head a-410; horse head a-420; horse head r-710; unitane o-110; unitane o-220; unitane or-150; unitane or-340; unitane or-342; unitane or-350; unitane or-540; unitane or-640; C.I. 77891; C.I. pigment white 6; cosmetic white C47-5175; 1700 white; a-elephant cream; austiox; bayeritian; flamenco; kronos; KH360; rayox; rutiox cr; ti-pure; titanium peroxide; titan white; trioxide (s); tronox; thioxide rhd; kronos cl 220; tioxide rsm; titanox ranc; austiox r-cr 3; R 680; RO 2; ti-pure r 900; thioxide ad-m; tioxide r.xl; cab-o-ti; ti-pure r 901; tipaque r 820; kronos rn 56; kronos rn 40p; bayertitan a; bayertitan r-u-f; thioxide r-cr; p25 (oxide); unitane or 650; unitane or 450; zopaque ldc; runa arh 20; runa arh 200; hombitan r 101d; hombitan r 610k; kronos 2073; unitane or 572; ti-pure r 101; ti-pure r 915; aerolyst 7710; anatase (TiO2); aquaspersabil R TiO2; bayertitan AN3; biogenic titania-100; ci77891; ci77891; CIpigment white 6; coverleaf MF; dioxotitanium; hallbrite T-97; kalixide CT (Vevy) ; kronos 2073; MT-01; MT-05; MT-100AQ; MT-100SA; MT-100SAS; MT-100TV; MT-100WP; MT-150W; MT-500B; MT-500H; oleosperse R TiO2; oleosperse TiO2; optisol OT50; optisol OTP1; photolite LY-S; photolite PK-S; siclone TD-150; titanium (IV) dioxide; titanium (IV) oxide; titanium dioxide FCC; titanium dioxide microfine dispersion in C12-15 alkyl benzoate 48.5; titanium dioxide microfinedispersion in caprylic-capric triglyderide 48.5; titanium dioxide microfine dispersion in octyl palmitate 48.5; titanium dioxide tech grade; titanium dioxide USP FCC hombitan AFDC; titanium oxide; titanium white; titanium (IV) oxide; titanium, dioxo trishield TS-510; unitane 0-110; uniwhite AO;

Titanium, the ninth most common element in the Earth`s crust, is a metal commonly found in plants and animals. Titanium naturally interacts with oxygen to form titanium oxides, commonly found in ores, indigenous dusts, sands and soils.Many people are familiar with titanium dioxide as an active ingredient in sunscreen. Titanium dioxide works as a UV filtering ingredient in sunscreen - it helps protect a person`s skin by blocking absorption of the sun`s ultraviolet light that can cause sunburn and is also linked to skin cancer.Titanium dioxide (TiO2) is considered as an inert and safe material and has been used in many applications for decades. However, with the development of nanotechnologies TiO2 nanoparticles, with numerous novel and useful properties, are increasingly manufactured and used. Therefore increased human and environmental exposure can be expected, which has put TiO2 nanoparticles under toxicological scrutiny. Mechanistic toxicological studies show that TiO2 nanoparticles predominantly cause adverse effects via induction of oxidative stress resulting in cell damage, genotoxicity, inflammation, immune response etc. The extent and type of damage strongly depends on physical and chemical characteristics of TiO2 nanoparticles, which govern their bioavailability and reactivity. Based on the experimental evidence from animal inhalation studies TiO2 nanoparticles are classified as "possible carcinogenic to humans" by the International Agency for Research on Cancer and as occupational carcinogen by the National Institute for Occupational Safety and Health. The studies on dermal exposure to TiO2 nanoparticles, which is in humans substantial through the use of sunscreens, generally indicate negligible transdermal penetration; however data are needed on long-term exposure and potential adverse effects of photo-oxidation products. Although TiO2 is permitted as an additive (E171) in food and pharmaceutical products we do not have reliable data on its absorption, distribution, excretion and toxicity on oral exposure. TiO2 may also enter environment, and while it exerts low acute toxicity to aquatic organisms, upon long-term exposure it induces a range of sub-lethal effects.Titanium dioxide occurs in nature as the 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. One of these is known as akaogiite and should be considered as an extremely rare mineral. It is mainly sourced from ilmenite ore. This is the most widespread form of 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 (1,112-1,472 °F). Titanium dioxide (TiO2) nanoparticles (NPs) are manufactured worldwide in large quantities for use in a wide range of applications. TiO2 NPs possess different physicochemical properties compared to their fine particle (FP) analogs, which might alter their bioactivity. Most of the literature cited here has focused on the respiratory system, showing the importance of inhalation as the primary route for TiO2 NP exposure in the workplace. TiO2 NPs may translocate to systemic organs from the lung and gastrointestinal tract (GIT) although the rate of translocation appears low. There have also been studies focusing on other potential routes of human exposure. Oral exposure mainly occurs through food products containing TiO2 NP-additives. Most dermal exposure studies, whether in vivo or in vitro, report that TiO2 NPs do not penetrate the stratum corneum (SC). In the field of nanomedicine, intravenous injection can deliver TiO2 nanoparticulate carriers directly into the human body. Upon intravenous exposure, TiO2 NPs can induce pathological lesions of the liver, spleen, kidneys, and brain. We have also shown here that most of these effects may be due to the use of very high doses of TiO2 NPs. There is also an enormous lack of epidemiological data regarding TiO2 NPs in spite of its increased production and use. However, long-term inhalation studies in rats have reported lung tumors. This review summarizes the current knowledge on the toxicology of TiO2 NPs and points out areas where further information is needed.

Uses & Benefits

Pure titanium dioxide is a fine, white powder that provides a bright, white pigment. Titanium dioxide has been used for a century in a range of industrial and consumer products, including paints, coatings, adhesives, paper, plastics and rubber, printing inks, coated fabrics and textiles, as well as ceramics, floor coverings, roofing materials, cosmetics, toothpaste, soap, water treatment agents, pharmaceuticals, food colorants, automotive products, sunscreen and catalysts.Titanium dioxide is produced in two main forms. The primary form, comprising over 98 percent of total production, is pigment grade titanium dioxide. The pigmentary form makes use of titanium dioxide`s excellent light-scattering properties in applications that require white opacity and brightness. The other form in which titanium dioxide is produced is as an ultrafine (nanomaterial) product. This form is selected when different properties, such as transparency and maximum ultraviolet light absorption, are required, such as in cosmetic sunscreens.

Pigment-grade Titanium Dioxide

Pigment-grade titanium dioxide is used in a range of applications that require high opacity and brightness. In fact, most surfaces and items that are white and pastel, and even dark shades of color, contain titanium dioxide. Pigment-grate titanium dioxide is used in a range of applications, including:

-Paints and Coatings: Titanium dioxide provides opacity and durability, while helping to ensure the longevity of the paint and protection of the painted surface.

-Plastics, Adhesives and Rubber: Titanium dioxide can help minimize the brittleness, fading and cracking that can occur as a result of light exposure. This can enhance the useful life of many plastic and rubber components used in vehicles, building materials and other exterior applications.

-Cosmetics: Pigment-grade titanium dioxide is use in some cosmetics to aid in hiding blemishes and brightening the skin. Titanium dioxide allows for the use of thinner coatings of make-up material for the same desired effect.

-Paper: Titanium dioxide is used to coat paper, making it whiter, brighter and more opaque.

-Food Contact Materials and Ingredients: The opacity to visible and ultraviolet light offered by titanium dioxide protects food, beverages, supplements and pharmaceuticals from premature degradation, enhancing the longevity of the product. Specific classes of high purity pigment-grade titanium dioxide are also used in drug tablets, capsule coatings and as a decorative aid in some foods.

Production

The production method depends on the feedstock. The most common mineral source is ilmenite. Ilmenite is treated with sulfuric acid to extract iron sulfate. The resulting synthetic rutile is further processed according to the specifications of the end user, i.e. pigment grade or otherwise. In another method for the production of synthetic rutile from ilmenite the Becher Process first oxidizes the ilmenite as a means to separate the iron component.Rutile is the second most abundant mineral sand. Rutile found in primary rock cannot be extracted hence the deposits containing rutile sand can be mined. Crude titanium dioxide (in the form of rutile or synthetic rutile) is purified by conversion 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 an oxygen flame or plasma at 1500-2000 K to give pure titanium dioxide while also regenerating chlorine. Aluminium chloride is often added to the process as a rutile promotor; the product is mostly anatase in its absence. The preferred raw material for the chloride process is natural rutile because of its high titanium dioxide content.

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, it is notable in that combined with zinc oxide , it is considered to be an effective sunscreen that is less harmful to coral reefs than sunscreens that include chemicals such as oxybenzone and octinoxate.Titanium dioxide is found in the majority of physical sunscreens 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. Nano-scaled (particle size of 30-40 nm) titanium dioxide particles are primarily used in sunscreen  lotion because they scatter visible light less than titanium dioxide pigments, while still providing UV protection. 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.It is used as a tattoo pigment and in styptic pencils. Titanium dioxide is produced in varying particle sizes, oil and water dispersible, and in certain grades for the cosmetic industry TiO2 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. Certain polymers used in the concrete or those used to impregnate concrete as a reinforcement are sometimes charged with titanium white pigment for UV shielding in the construction industry, but it only delays the oxidative photodegradation of the polymer in question, which is said to "chalk" as it flakes off due to lowered impact strength and may crumble after years of exposure in direct sunlight if UV stabilizers have not been included.

Uses & Benefits
Pure titanium dioxide is a fine, white powder that provides a bright, white pigment. Titanium dioxide has been used for a century in a range of industrial and consumer products, including paints, coatings, adhesives, paper, plastics and rubber, printing inks, coated fabrics and textiles, as well as ceramics, floor coverings, roofing materials, cosmetics, toothpaste, soap, water treatment agents, pharmaceuticals, food colorants, automotive products, sunscreen and catalysts.Titanium dioxide is produced in two main forms. The primary form, comprising over 98 percent of total production, is pigment grade titanium dioxide. The pigmentary form makes use of titanium dioxide's excellent light-scattering properties in applications that require white opacity and brightness. The other form in which titanium dioxide is produced is as an ultrafine (nanomaterial) product. This form is selected when different properties, such as transparency and maximum ultraviolet light absorption, are required, such as in cosmetic sunscreens.
Pigment-grade Titanium Dioxide
Pigment-grade titanium dioxide is used in a range of applications that require high opacity and brightness. In fact, most surfaces and items that are white and pastel, and even dark shades of color, contain titanium dioxide. Pigment-grate titanium dioxide is used in a range of applications, including:
-Paints and Coatings: Titanium dioxide provides opacity and durability, while helping to ensure the longevity of the paint and protection of the painted surface.
-Plastics, Adhesives and Rubber: Titanium dioxide can help minimize the brittleness, fading and cracking that can occur as a result of light exposure. This can enhance the useful life of many plastic and rubber components used in vehicles, building materials and other exterior applications.
-Cosmetics: Pigment-grade titanium dioxide is use in some cosmetics to aid in hiding blemishes and brightening the skin. Titanium dioxide allows for the use of thinner coatings of make-up material for the same desired effect.
-Paper: Titanium dioxide is used to coat paper, making it whiter, brighter and more opaque
-Food Contact Materials and Ingredients: The opacity to visible and ultraviolet light offered by titanium dioxide protects food, beverages, supplements and pharmaceuticals from premature degradation, enhancing the longevity of the product. Specific classes of high purity pigment-grade titanium dioxide are also used in drug tablets, capsule coatings and as a decorative aid in some foods.
Production
The production method depends on the feedstock. The most common mineral source is ilmenite. Ilmenite is treated with sulfuric acid to extract iron sulfate. The resulting synthetic rutile is further processed according to the specifications of the end user, i.e. pigment grade or otherwise. In another method for the production of synthetic rutile from ilmenite the Becher Process first oxidizes the ilmenite as a means to separate the iron component.Rutile is the second most abundant mineral sand. Rutile found in primary rock cannot be extracted hence the deposits containing rutile sand can be mined. Crude titanium dioxide (in the form of rutile or synthetic rutile) is purified by conversion 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 an oxygen flame or plasma at 1500-2000 K to give pure titanium dioxide while also regenerating chlorine. Aluminium chloride is often added to the process as a rutile promotor; the product is mostly anatase in its absence. The preferred raw material for the chloride process is natural rutile because of its high titanium dioxide content.
 

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, it is notable in that combined with zinc oxide , it is considered to be an effective sunscreen that is less harmful to coral reefs than sunscreens that include chemicals such as oxybenzone and octinoxate.Titanium dioxide is found in the majority of physical sunscreens 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. Nano-scaled (particle size of 30-40 nm) titanium dioxide particles are primarily used in sunscreen lotion because they scatter visible light less than titanium dioxide pigments, while still providing UV protection. 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.It is used as a tattoo pigment and in styptic pencils. Titanium dioxide is produced in varying particle sizes, oil and water dispersible, and in certain grades for the cosmetic industry TiO2 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. Certain polymers used in the concrete or those used to impregnate concrete as a reinforcement are sometimes charged with titanium white pigment for UV shielding in the construction industry, but it only delays the oxidative photodegradation of the polymer in question, which is said to "chalk" as it flakes off due to lowered impact strength and may crumble after years of exposure in direct sunlight if UV stabilizers have not been included.

Chemical and physical properties
Titanium dioxide naturally occurs in the three modifications rutile, anatase and brookite.
Rutile (Ti[6]O[3] 2) and anatase crystallize in ditetragonal‐dipyramidal forms, but differ in their space group. Brookite crystallizes in a rhombic‐dipyramidal form (see Ramdohr and Strunz 1978; Rösler 1991).
Rutile is the thermodynamically stable form of titanium dioxide. In this structure, the TiO6 coordination octahedrons are each connected with two further TiO6 coordination octahedrons via common edges, resulting in long chains parallel to the c axis. The titanium ions form a spatially centred tetragonal elementary cell, the oxygen ions a somewhat distorted, hexagonally dense package, half of whose octahedron gaps are occupied by titanium ions (Holleman and Wiberg 2007; Matthes 1990).

As a result of electrostatic valence compensation, the exchanging of Ti4+ ions with Fe3+ ions makes possible the insertion of Nb5+ and Ta5+ in the rutile lattice (Matthes 1990). Other elements frequently contained in rutile are Fe, Mg, Cr and Mn.
Rutile possesses a high refraction index, which is made use of in the production of bleaching agents (pigment, paper, textile and plastics industry) and in cosmetics. In anatase, the TiO6 coordination octahedrons are connected with four further TiO6 octahedrons via common edges. To date, this structural type has not been discovered in any other mineral (Holleman and Wiberg 2007; Matthes 1990; Ramdohr and Strunz 1978). Anatase transforms monotropically into rutile at 915°C (Rösler 1991). In its natural form, anatase is of practically no importance as a raw material at present.
Depending on the process used, either rutile or anatase is obtained in the production of titanium dioxide.
In brookite, which crystallizes orthorhombically (dipyramidally) into small flakes, all TiO6 coordination octahedrons are linked to three other TiO6 coordination octahedrons via common edges. Brookite likewise transforms monotropically into rutile at 915°C. Brookite is of no economic importance at present (Holleman and Wiberg 2007).
The iron titanate ilmenite (FeTiO3) is a particularly important raw material in the production of "titanium white" paint.
Titanite crystals (CaTi[OSiO4]) frequently contain FeO, Al2O3, Y2O3 and Ce2O3, which often cause great deviations from the general formula. For example, Y replaces Ca, which has the same ion radius, while Al or Fe enter the crystal lattice for Ti, or F for O, as valency compensators.
Titanium dioxide has amphoteric properties. On the one hand, it dissolves in concentrated sulfuric acid to form Ti(SO4)2 and in concentrated nitric acid to form Ti(NO3)4×H2O. On the other hand, in smelting with alkaline hydroxides or carbonates, it forms titanates which are easily hydrolyzed back to hydratized titanium dioxide in the presence of water (Holleman and Wiberg 2007).
Through fusion with metal oxides, titanium dioxide forms mixed oxides with ilmenite (MgTiO3, MnTiO3, FeTiO3, CoTiO3, NiTiO3), perowskite (CaTiO3, SrTiO3, BaTiO3) or spinell structures.
Photocatalytic properties of titanium dioxide
Titanium dioxide particles are semiconductors and are used in the form of anatase and rutile as photocatalyzers; anatase is more active than rutile (Dunford et al. 1997; Fujishima et al. 2000; Hirakawa et al. 2004; Schindler and Kunst 1990).
In a study, the duration of various reactions during the degradation of chemical substances in water with UV irradiation and in the presence of high titanium dioxide concentrations was determined. These photocatalytic reactions were found to take between a few minutes and more than one hour, and were triggered during irradiation with ultraviolet light by the formation of radicals (Legrini et al. 1993).
The photocatalytic effects of titanium dioxide and the differences between anatase and rutile are the result of the different position of the energy level of the electrons in the conduction band of the two titanium dioxide modifications. Because of the conduction state produced by ultraviolet light, the stimulated state is also called photoconductivity.
In the case of anatase, the conduction band is about 0.2 eV above the zero level, that means the stimulated electrons are not bound, the excitation level is 3.2 eV.
In the case of rutile, the excitation level is 3.0 eV. In the conduction band, the electrons are loosely bound at 0.1 eV (Dunford et al. 1997; Kim et al. 2001; Vogelsang 1999). These semiconductor properties make titanium dioxide (especially anatase) interesting from a technical point of view as a material in the photovoltaic field, as excitation of the electrons is triggered by light. For excitation, ultraviolet light with a wavelength below 350 nm is used. This light is absorbed by titanium dioxide via resonance absorption with a high cross‐section; ultraviolet light with wavelengths of more than 350 nm is reflected by titanium dioxide particles or emitted in the form of light at longer wavelengths (Martin et al. 1994).
In the case of doped titanium dioxide or pure titanium dioxide in contact with electrolytes, the valence and conduction bands are locally distorted (Fox and Dulay 1993). As a result, the resonance absorption is interrupted and the energy released on recombination is emitted in the form of light at wavelengths in the neighbouring longer wavelength spectrum (Martin et al. 1994). Non‐exponential decay curves can be produced as different states of stimulation with different half‐lives are passed through during decay. The reflection spectrum and/or emission spectrum then contains less short‐wave ultraviolet light.
The duration of the excitation states of the electrons in the conduction band was determined using microwave photoconductivity (Schindler and Kunst 1990). Powdered anatase and rutile were excited by a laser pulse (λ = 266 nm, T = 20 ns, E = 0.1 mJ/cm2 and E = 0.5 mJ/cm2). In a more recent study, values between 28 and 1200 ns were determined for the half‐life of the excitation states of thermally pretreated (150-900°C) anatase (Colbeau‐Justin et al. 2003). These values are independent of the excitation level. In the case of rutile, the excitation state decays much more rapidly than with anatase. This phenomenon has been observed also at wavelengths of 266 nm and 355 nm of the irradiated light (Colbeau‐Justin et al. 2003). Doping and surface treatment modify the temporal course of the decay reaction. It must be noted that commercially available titanium dioxide products (for example, P25 Degussa) may consist of mixtures of anatase and rutile, and the decay reaction of the excitation state can be delayed for periods as long as several seconds (Schindler and Kunst 1990).
In in vitro experiments with cells, ultraviolet light causes titanium dioxide particles to become excited during irradiation. They are thus able to stimulate radical formation in the fluid or in cells of a cell culture by electron transfer (Legrini et al. 1993; Martin et al. 1994). This can result also in DNA damage in the treated cells (Hirakawa et al. 2004). In one study, the radical yield and the toxic effects of titanium dioxide on CHO cells (a cell line derived from Chinese hamster ovary; source: Riken Cell Bank, Tukuba, Japan) were investigated after UVA irradiation for 24 hours (λ < 352 nm, E = 36 mJ/cm2). It was found that although also the size of the crystals had a great influence on the number of radicals formed, anatase was nevertheless able to release a larger number of radicals than rutile (Uchino et al. 2002).
Conclusion
Titanium dioxide is a photocatalytic substance whose excitation state has a short half‐life (ns to µs). As a result of this short half‐life, no sequel reactions of any extent worth mentioning can be produced in the lungs by stimulated titanium dioxide. This property should be considered also when evaluating the in vitro studies available.
Occurrence
Titanium is the ninth most frequent element in the earth's crust. Although its occurance is widespread, it is usually only found in low concentrations. In mineral form, it is found in magmatic, metamorphic and secondary deposits. Titanium is frequent in iron ores, above all in ilmenite (FeTiO3). Further important titanium minerals are the three different crystal forms of titanium dioxide (TiO2), rutile, anatase and brookite, and titanite (CaTiO[SiO4]) and perowskite (CaTiO3).
Deposits and main countries of origin
Primary titanium mineral deposits are found in Canada, Russia, the USA, Finland and Norway. The greatest heavy mineral sand deposits (secondary deposits) are found before the Australian coast, others are known in India, Sri Lanka, Sierra Leone and South Africa (Wirtschaftsvereinigung Bergbau e.V. 1983). The world production of ilmenite and rutile was 6.8 million tonnes per year in 1996 (Deutsches Institut für Wirtschaftsförderung 2000).
Association and secondary mineralization (paragenesis)
According to the deposit type, different secondary minerals (paragenesis) are found. In addition to ilmenite and rutile, mainly zirconium, magnetite, cassiterite and monazite are found in heavy mineral sands. Quartz, calcite, haematite, feldspars, corundum, garnet, chromite, olivine, apatite, magnetite and albite occur in the remaining deposit types together with the titanium minerals rutile, anatase, titanite and ilmenite (Pohl 2005; Ramdohr and Strunz 1978; Rösler 1991; Strubel and Zimmer 1991) (see also Table 1).
Production and use: Raw materials
The forms of titanium used as raw materials are almost exclusively ilmenite and rutile. Brookite plays only a minor role. In future, also perowskite and anatase could gain importance as raw materials (Holleman and Wiberg 2007; Pohl and Petraschek 2005).
Production and processing
For production, the mineral ore is first broken down and ground, then sieved and freed from the matrix by gravity separation. Magnetite is separated by magnetic separation, sulfate and iron by reduction processes. The titanium ore thus obtained is further enriched by flotation (Holleman and Wiberg 2007; Pohl and Petraschek 1997).
Chloride process
Ilmenite or natural rutile are transformed into titanium tetrachloride vapour using chlorine and coke at 950°C. After cleansing the gas by distillation, it is converted to fine rutile. No pigments with anatase structure can be obtained in the chloride process.
The chloride process is preferred, as the chlorine used can be recovered (Holleman and Wiberg 2007).
Sulfate process
The titanium slag obtained by reduction is decomposed at 100-180°C with concentrated sulfuric acid, and subsequently oxidized and filtered off to obtain TiO2 × H2O. The titanium dioxide hydrate is ignited in a rotary kiln at 800-1000°C. In this process, the crystal structure and particle size of the pigments are determined by the processing method:
at 800-1000°C fine grain anatase is produced,
at temperatures greater than 1000°C coarse grain rutile is formed,
at 800-1000°C in the presence of rutile nuclei, fine‐grain rutile is produced (Holleman and Wiberg 2007).
Uses
In the fields of medicine and pharmacy, the substance is used in surgical prostheses and as filler in pharmaceuticals.
Pigmentary titanium dioxide (especially in its rutile structure) is used as a brightener in the paint and coating industry. Rutile pigments have a higher double refraction, and consequently a better covering power than anatase pigments.
In the textile industry, only anatase pigments can be used, as rutile pigments would damage the spinning machines as a result of their greater hardness. As titanium dioxide very effectively absorbs short wave ultraviolet light, it is used in cosmetics, for example in sunscreens or lotions (Nordman and Berlin 1986). Nowadays, sun lotions usually contain both organic compounds, such as butylmethoxy dibenzoyl methane or 4‐methylbenzylidene camphor, and inorganic titanium dioxide and zinc oxide as synergistically interacting ultraviolet filter substances. As they partially reflect sunlight, the particles act as "nano reflectors".
The photocatalytic activity of titanium dioxide in vivo is a cause of increasing concern. In order to minimize adverse effects, coated titanium dioxide is now frequently used in cosmetic preparations. The coating must be stable under the conditions of use. Tests with coated titanium dioxide nano particles in sun lotions using laser‐induced plasma spectroscopy revealed no changes in the mechanical stability and suspension properties of the lotion (BGIA 2004; 2008).
Surface treatment
Special surface coatings are sometimes used to make the material hydrophobic or hydrophilic, or reduce its agglomeration capacity, as required. The most important surface coatings presently in use are listed in Table 2.
The length of the carbon polymer chains used in the surface treatment of titanium dioxide particles must be greater than the range of the van der Waals forces, but short enough to avoid the formation of steric barriers able to impede particle movement. The polarity of the chains must be suited to the solution or the dispersion medium.
Analytical procedures
Procedures to determine the respirable and the inhalable fractions are found, for example, in the BGIA folder (BGIA 2008). However, should it be necessary to specifically determine the proportion of titanium and its compounds in dusts, the analytical methods described in the following may be used.
Characterization of the procedure
The procedures used in practice for titanium and its compounds are exclusively procedures for "elemental analysis", in other words, it is not possible to differentiate between titanium (as metal) and the various titanium compounds with these methods. Therefore, the analytical results always refer to the total amount of titanium in the collected dust; worst case estimates for specific compounds are possible using stoichiometric calculation.
Individual crystalline titanium compounds can be qualitatively differentiated by means of X‐ray diffraction. However, there are no analytical procedures established for occupational safety on the basis of this analytical method in which the proportion of a specific titanium compound can be determined quantitatively.
Notes on the procedure
Dusts containing titanium are collected on a filter. The collected dust is subjected to acid hydrolysis adapted for the poorly soluble titanium dioxide, and the resulting solution is then analyzed.
Titanium dioxide, also known as titanium(IV) oxide or titania /taɪˈteɪniə/, is the naturally occurring oxide of titanium, chemical formula TiO
2. When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. Generally, it is sourced from ilmenite, rutile, and anatase. 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.[4][5][6] 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 $13.2 billion.
Occurrence
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 is an orthorhombic α-PbO2-like form known as brookite, both of which can be found at the Ries crater in Bavaria.[8][9][10] It is mainly sourced from ilmenite ore. This is the most widespread form of 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).
Titanium dioxide has eight modifications - in addition to rutile, anatase, akaogiite, and brookite, three metastable phases can be produced synthetically (monoclinic, tetragonal, and orthorombic), and five high-pressure forms (α-PbO2-like, baddeleyite-like, cotunnite-like, orthorhombic OI, and cubic phases) also exist:
The cotunnite-type phase was claimed by L. Dubrovinsky and co-authors 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.[19] 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)[20] and bulk modulus (~300 GPa).[21][22]
The oxides are commercially important ores of titanium. The metal is also be mined from other ores such as ilmenite or leucoxene, or one of the purest forms, rutile beach sand. Star sapphires and rubies get their asterism from rutile impurities present.
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.
Molten titanium dioxide has a local structure in which each Ti is coordinated to, on average, about 5 oxygen atoms. This is distinct from the crystalline forms in which Ti coordinates to 6 oxygen atoms.
Production
Evolution of the global production of titanium dioxide according to process
The production method depends on the feedstock. The most common mineral source is ilmenite. The abundant rutile mineral sand can also be purified with the chloride process or other processes. Ilmenite is converted into pigment grade titanium dioxide via either the sulfate process or the chloride process. Both sulfate and chloride processes produce the 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.[26]
Plants using the Sulfate Process require ilmenite concentrate (45-60% TiO2) or pretreated feedstocks as suitable source of titanium.[27] In the sulfate process, ilmenite is treated with sulfuric acid to extract iron(II) sulfate pentahydrate. The resulting synthetic rutile is further processed according to the specifications of the end user, i.e. pigment grade or otherwise.[28] In another method for the production of synthetic rutile from ilmenite the Becher Process first oxidizes the ilmenite as a means to separate the iron component.
An alternative process, known as the chloride process converts ilmenite or other titanium sources to titanium tetrachloride via reaction with elemental chlorine, which is then purified by distillation, and reacted with oxygen to regenerate chlorine and produce the titanium dioxide. Titanium dioxide pigment can also be produced from higher titanium content feedstocks such as upgraded slag, rutile, and leucoxene via a chloride acid process.
The five largest TiO
2 pigment processors are in 2019 Chemours, Cristal Global, Venator, Kronos, and Tronox, which is the largest one.[29][30] Major paint and coating company end users for pigment grade titanium dioxide include Akzo Nobel, PPG Industries, Sherwin Williams, BASF, Kansai Paints and Valspar.[31] Global TiO
2 pigment demand for 2010 was 5.3 Mt with annual growth expected to be about 3-4%.[32]
Specialized methods
For specialty applications, TiO2 films are prepared by various specialized chemistries.[33] Sol-gel routes involve the hydrolysis of titanium alkoxides, such as titanium ethoxide:
Ti(OEt)4 + 2 H2O → TiO2 + 4 EtOH
This technology is suited for the preparation of films. A related approach that also relies on molecular precursors involves chemical vapor deposition. In this application, the alkoxide is volatilized and then decomposed on contact with a hot surface:
Ti(OEt)4 → TiO2 + 2 Et2O
Applications
The most important application areas are paints and varnishes as well as paper and plastics, which account for about 80% of the world's titanium dioxide consumption. Other pigment applications such as printing inks, fibers, rubber, cosmetic products, and food account for another 8%. The rest is used in other applications, for instance the production of technical pure titanium, glass and glass ceramics, electrical ceramics, metal patinas, catalysts, electric conductors, and chemical intermediates.
Pigment
First mass-produced in 1916,[35] 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. 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.[36] Approximately 4.6 million tons of pigmentary TiO2 are used annually worldwide, and this number is expected to increase as use continues to rise.
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), and most toothpastes. 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.
TiO2 has been flagged as possibly carcinogenic. In 2019, it was present in two thirds of toothpastes on the French market. Bruno Le Maire, a minister in the Edouard Philippe government, promised in March 2019 to remove it from that and other alimentary uses.
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.[39] 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[40] One example of a pearlescent pigment is Iriodin, based on mica coated with titanium dioxide or iron (III) oxide.[41]

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 is less harmful to coral reefs than sunscreens that include chemicals such as oxybenzone and octinoxate.
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)[42] 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.[37] 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 blocks both UV-A and UV-B radiation, which is used in sunscreens and other cosmetic products. It is safe to use and it is better to environment than organic UV-absorbers.[43]
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.[44]
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, oil and water dispersible, and in certain grades for the cosmetic industry.
Research
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,[45][46] although the {101} planes are thermodynamically more stable and thus more prominent in most synthesised and natural anatase,[47] 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.[48] 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.[49] 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[50] and published in 1972.[51] The process on the surface of the titanium dioxide was called the Honda-Fujishima effect (ja:本多-藤嶋効果).[50] Titanium dioxide, in thin film and nanoparticle form has 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.[52] 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.[53] Visible-light-active nanosized anatase and rutile has been developed for photocatalytic applications.
In 1995 Fujishima and his group discovered the superhydrophilicity phenomenon for titanium dioxide coated glass exposed to sun light.[50] 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[56] or paints, can substantially reduce concentrations of airborne pollutants such as volatile organic compounds and nitrogen oxides.[57] A cement that uses titanium dioxide as a photocatalytic component, produced by Italcementi Group, was included in Time Magazine's Top 50 Inventions of 2008.
Attempts have been made to photocatalytically mineralize pollutants (to convert into CO2 and H2O) in waste water.[59] TiO2 offers great potential as an industrial technology for detoxification or remediation of wastewater due to several factors:
The process uses natural oxygen and sunlight and thus occurs under ambient conditions; it is wavelength selective and is accelerated by UV light.
The photocatalyst is inexpensive, readily available, non-toxic, chemically and mechanically stable, and has a high turnover.
The formation of photocyclized intermediate products, unlike direct photolysis techniques, is avoided.
Oxidation of the substrates to CO2 is complete.
TiO2 can be supported as thin films on suitable reactor substrates, which can be readily separated from treated water.
The photocatalytic destruction of organic matter is also exploited in photocatalytic antimicrobial coatings,[62] which are typically thin films applied to furniture in hospitals and other surfaces susceptible to be contaminated with bacteria, fungi, and viruses.
Health and safety
Titanium dioxide is incompatible with strong reducing agents and strong acids.[67] Violent or incandescent reactions occur with molten metals that are electropositive, e.g. aluminium, calcium, magnesium, potassium, sodium, zinc and lithium.
Many sunscreens use nanoparticle titanium dioxide (along with nanoparticle zinc oxide) which, despite reports of potential health risks, is not actually absorbed through the skin. Other effects of titanium dioxide nanoparticles on human health are not well understood.
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. 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.[74] 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, 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.[75] Studies have also found that titanium dioxide nanoparticles cause inflammatory response and genetic damage in mice.
The mechanism by which TiO
2 may cause cancer is unclear. Molecular research suggests that cell cytotoxicity due to TiO
2 results from the interaction between TiO
2 nanoparticles and the lysosomal compartment, independently of the known apoptotic signalling pathways.
The body of research regarding the carcinogenicity of different particle sizes of titanium dioxide has led the US National Institute for Occupational Safety and Health to recommend 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.[79] These recommendations reflect the findings in the research literature that show smaller titanium dioxide particles are more likely to pose carcinogenic risk than the larger titanium dioxide particles.
There is some evidence the rare disease yellow nail syndrome may be caused by titanium, either implanted for medical reasons or through eating various foods containing titanium dioxide.
Companies such as Mars and Dunkin' Donuts dropped titanium dioxide from their merchandise in 2015 after public pressure.[81] However, Andrew Maynard, director of Risk Science Center at the University of Michigan, downplayed 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.[82] Still, size distribution analyses showed that batches of food-grade TiO₂ always comprise a nano-sized fraction as inevitable byproduct of the manufacturing processes.
Environmental waste introduction
Titanium dioxide (TiO₂) is mostly introduced into the environment as nanoparticles via wastewater treatment plants.[84] 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.[84] 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.[84] 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.