Titanium dioxide

Uses

Titanium (IV) dioxide (TiO2), also known as rutile, is one of the best-known compounds used as a paint pigment. Of the 3.06 million metric tons of Ti02 used in 1992, 51 % was used in coatings, 19% in plastics, 14% in paper, and the balance of 8% in several different applications such as elastomers, ceramics, cosmetics, and foods. It is ideal for paints exposed to severe temperatures and marine climates because of its inertness and self-cleaning attributes. It is also used in manufacture of glassware, ceramics, enamels, welding rods, and floor coverings.

Description

Titanium dioxide, TiO2, is a white powder and has the greatest hiding power of all white pigments. It is noncombustible; however, it is a powder and, when suspended in air, may cause a dust explosion if an ignition source is present. It is not listed in the DOT Hazardous Materials Table, and the DOT does not consider it hazardous in transportation. The primary uses are as a white pigment in paints, paper, rubber, and plastics; in cosmetics; in welding rods; and in radioactive decontamination of the skin.

Chemical Properties

White, amorphous, odorless, and tasteless nonhygroscopic powder. Although the average particle size of titanium dioxide powder is less than 1 mm, commercial titanium dioxide generally occurs as aggregated particles of approximately 100 mm diameter.
Titanium dioxide may occur in several different crystalline forms: rutile; anatase; and brookite. Of these, rutile and anatase are the only forms of commercial importance. Rutile is the more thermodynamically stable crystalline form, but anatase is the form most commonly used in pharmaceutical applications.

Chemical Properties

The naturally occurring dioxide exists in three crystal forms: anatase, rutile and brookite. While rutile, the most common form, has an octahedral structure. Anatase and brookite have very distorted octahedra of oxygen atoms surrounding each titanium atom. In such distorted octahedral structures, two oxygen atoms are relatively closer to titanium than the other four oxygen atoms. Anatase is more stable than the rutile form by about 8 to 12 kJ/mol (Cotton, F.A., Wilkinson, G., Murillo, C.A and M Bochmann. 1999. Advanced Inorganic Chemistry, 6th ed, p. 697, New York: John Wiley & Sons) Other physical properties are: density 4.23g/cm3; Mohs hardness 5.8 g/cm3 ( anatase and brookite) and 6.2 g/cm3 ( rutile); index of refraction 2.488 (anatase), 2.583 (brookite) and 2.609 (rutile); melts at 1,843°C; insoluble in water and dilute acids; soluble in concentrated acids.

Chemical Properties

Ttitanium dioxide is an odorless white powder.

Physical properties

Metastable over long periods of time despite being less thermodynamically stable than rutile. However, above 700°C, the irreversible and rapid monotropic conversion of anatase to rutile occurs. It exhibits a greater transparency in the near-UV than rutile. With an absorption edge at 385 nm, anatase absorbs less light at the blue end of the visible spectrum and has a blue tone.

Physical properties

The naturally occurring dioxide exists in three crystal forms: anatase, rutile and brookite. While rutile, the most common form, has an octahedral structure. Anatase and brookite have very distorted octahedra of oxygen atoms surrounding each titanium atom. In such distorted octahedral structures, two oxygen atoms are relatively closer to titanium than the other four oxygen atoms. Anatase is more stable than the rutile form by about 8 to 12 kJ/mol (Cotton, F.A., Wilkinson, G., Murillo, C.A and M Bochmann. 1999. Advanced Inorganic Chemistry, 6th ed, p. 697, New York: John Wiley & Sons) Other physical properties are: density 4.23g/cm3; Mohs hardness 5.8 g/cm3 ( anatase and brookite) and 6.2 g/cm3 ( rutile); index of refraction 2.488 (anatase), 2.583 (brookite) and 2.609 (rutile); melts at 1,843°C; insoluble in water and dilute acids; soluble in concentrated acids.

Occurrence

Titanium dioxide occurs in nature in the crystalline forms rutile, anatase, and brookite. Rutile and anatase are manufactured in large quantities, which are primarily used as pigments, but also as catalysts and in ceramics.

Characteristics

Titanium dioxide (C.I. Pigment White 6) is of outstanding importance as a white pigment because of its scattering properties, its chemical stability, its biological inertness, and its lack of toxicity. The pigment is frequently coated with colorless organic or inorganic compounds of low solubility to improve its weather resistance, lightfastness, and dispersibility.

Uses

Titanium dioxide is an extreme white and bright compound with high index of refraction. In paints it is a white pigment and an opacifying agent.It is in house paints, water paints, lacquers, enamels, paper filling and coating, rubber, plastics, printing ink, synthetic fabrics, floor coverings, and shoe whiteners. Also, it is used in colorants for ceramics and coatings for welding rods. A rutile form of the dioxide is used in synthetic gem stones.

Uses

Airfloated ilmenite is used for titanium pigment manufacture. Rutile sand is suitable for welding-rod-coating materials, as ceramic colorant, as source of titanium metal. As color in the food industry. Anatase titanium dioxide is used for welding-rod-coatings, acid resistant vitreous enamels, in specification paints, exterior white house paints, acetate rayon, white interior air-dry and baked enamels and lacquers, inks and plastics, for paper filling and coating, in water paints, tanners' leather finishes, shoe whiteners, and ceramics. High opacity and tinting values are claimed for rutile-like pigments.

Uses

Titanium Dioxide is a white pigment that disperses in liquids and possesses great opacifying power. the crystalline modifications of titanium dioxide are rutile and anatase, of which only anatase finds use as a color additive.

Uses

titanium dioxide (TiO2) is one of the 21 FDA-approved sunscreen chemicals with an approved usage level of 2 to 25 percent. When applied, titanium dioxide remains on the skin’s surface, scattering uV light. It is often used in conjunction with other sunscreen chemicals to boost the product’s SPF value, thus reducing the risk of irritation or allergies attributed to excessive usage of chemical sunscreens. Its incorporation into sunscreen formulations, makeup bases, and daytime moisturizers depends on the particular size of titanium dioxide employed. The smaller the particle size, the more unobtrusive Tio2’s application. Large particles, on the other hand, leave a whitish wash or look on the skin. Some companies list “micro” or “ultra” when referring to the size of the titanium dioxide particle. According to some sources, titanium dioxide could be the ideal uVA/uVB protection component given its chemical, cosmetic, and physical characteristics. Titanium dioxide is also used to provide a white color to cosmetic preparations.

Production Methods

There are two major processes for the manufacture of titanium dioxide pigments, namely sulfate route and chloride route. In the sulfate process, the ore limonite, FeOTiO2, is dissolved in sulfuric acid and the resultant solution is hydrolyzed by boiling to produce a hydrated oxide, while the iron remains in solution. The precipitated titanium hydrate is washed and leached free of soluble impurities. Controlled calcinations at about 1000°C produce pigmentary titanium dioxide of the correct crystal size distribution; this material is then subjected to a finishing coating treatment and milling.
The chloride process uses gaseous chlorination of mineral rutile, followed by distillation and finally a vapor phase oxidation of the titanium tetrachloride.

Production Methods

Titanium dioxide occurs naturally as the minerals rutile (tetragonal structure), anatase (tetragonal structure), and brookite (orthorhombic structure).
Titanium dioxide may be prepared commercially by either the sulfate or chloride process. In the sulfate process a titanium containing ore, such as ilemenite, is digested in sulfuric acid. This step is followed by dissolving the sulfates in water, then precipitating the hydrous titanium dioxide using hydrolysis. Finally, the product is calcinated at high temperature. In the chloride process, the dry ore is chlorinated at high temperature to form titanium tetrachloride, which is subsequently oxidized to form titanium dioxide.

Definition

ChEBI: Titanium dioxide is a titanium oxide with the formula TiO2. A naturally occurring oxide sourced from ilmenite, rutile and anatase, it has a wide range of applications. It has a role as a food colouring.

Application

Preparation

Titanium dioxide is mined from natural deposits. It also is produced from other titanium minerals or prepared in the laboratory. Pigment-grade dioxide is produced from the minerals, rutile and ilmenite. Rutile is converted to pigment grade rutile by chlorination to give titanium tetrachloride, TiCl4. Anhydrous tetrachloride is converted back to purified rutile form by vapor phase oxidation.
Anatase form is obtained by hydrolytic precipitation of titanium(IV) sulfate on heating. The mineral ilmenite is treated with concentrated sulfuric acid. Heating the sulfate solution precipitates hydrous titanium oxide. The precipitate is calcined to expel all water.
Titanium dioxide also can be prepared by heating Ti metal in air or oxygen at elevated temperatures.

Composition

This material is visually a brilliant white pigment which also has anti-inflammatory properties. Two crystal types of TiO2 occur: anatase and rutile. In order to produce these crystals, there are two manufacturing processes that are employed: (1) The sulfate manufacturing process has the ability to produce either type of crystal, while (2) the chloride manufacturing process produces only rutile crystals.

General Description

Two main physico-chemically distinct polymorphs of TiO₂ are anatase and rutile. Anatase has a higher photocatalytic activity than rutile but is thermodynamically less stable.

Hazard

Lower respiratory tract irritant. Possible carcinogen.

Health Hazard

Titanium dioxide is a mild pulmonary irritant and is generally regarded as a nuisance dust.

Flammability and Explosibility

Not classified

Pharmaceutical Applications

Titanium dioxide is widely used in confectionery, cosmetics, and foods, in the plastics industry, and in topical and oral pharmaceutical formulations as a white pigment.
Owing to its high refractive index, titanium dioxide has lightscattering properties that may be exploited in its use as a white pigment and opacifier. The range of light that is scattered can be altered by varying the particle size of the titanium dioxide powder. For example, titanium dioxide with an average particle size of 230nm scatters visible light, while titanium dioxide with an average particle size of 60nm scatters ultraviolet light and reflects visible light.
In pharmaceutical formulations, titanium dioxide is used as a white pigment in film-coating suspensions, sugar-coated tablets, and gelatin capsules. Titanium dioxide may also be admixed with other pigments.
Titanium dioxide is also used in dermatological preparations and cosmetics, such as sunscreens.

Safety Profile

A nuisance dust. A human skin irritant. Questionable carcinogen with experimental carcinogenic, neoplastigenic, and tumorigenic data. Violent or incandescent reaction with metals at high temperatures (e.g., aluminum, calcium, magnesium, potassium, sodium, zinc, lithium). See also TITANIUM COMPOUNDS.

Safety

Titanium dioxide is widely used in foods and oral and topical pharmaceutical formulations. It is generally regarded as an essentially nonirritant and nontoxic excipient.

Potential Exposure

Titanium dioxide is a white pigment used as a pigment in paint; in the rubber, plastics, ceramics, paint, and varnish industries, in dermatological preparations; and is used as a starting material for other titanium compounds; as a gem; in curing concrete; and in coatings for welding rods. It is also used in paper and cardboard manufacture.

Carcinogenicity

Carcinogenesis. In a 1985 study, rats (CD) were exposed to graded airborne concentrations (0, 10, 50, and 250mg/m³) of TiO2 6 h/day, 5 days/week, for 2 years. The majority of the particles were in the respirable range (84% ≤13 mmMMD). All responses were confined to the lungs. At the lowest dose, the histopathological evaluation of the lungs revealed dust-laden macrophages in the alveolar ducts and adjacent alveoli with pneumocyte hyperplasia. At the two highest concentrations, there were increases in lung weight, accumulation of dust in the macrophages, foamy macrophage responses, type II pneumocyte hyperplasia, alveolar proteinosis, alveolar bronchiolization, cholesterol granulomas, focal pleurisy, and dust deposition in the tracheobronchiolar lymph nodes. At the 250mg/m³ exposure concentration, bronchiole alveolar adenomas (males: control 2/79, 250mg/m³ 12/79; females: control 0/79, 250mg/m³ 13/79) increased. Additionally, 13/79 females at the 250mg/m³ dose showed squamous cell carcinoma, compared with none in 79 controls. Theauthorsnoted that this responsemight have little biological relevance to humans because of the overload of respiratory clearance mechanisms and also pointed out that the type, location, and development of the tumors were different from those in human lung tumors. It is not clear that the nasal cavity epithelium was examined. However, the nasal cavity load would be expected to be higher in the rats because of anatomic structure, whereas the lung deposition should be higher in humans because we are, in part, mouth breathers.

storage

Titanium dioxide is extremely stable at high temperatures. This is due to the strong bond between the tetravalent titanium ion and the bivalent oxygen ions. However, titanium dioxide can lose small, unweighable amounts of oxygen by interaction with radiant energy. This oxygen can easily recombine again as a part of a reversible photochemical reaction, particularly if there is no oxidizable material available. These small oxygen losses are important because they can cause significant changes in the optical and electrical properties of the pigment.
Titanium dioxide should be stored in a well-closed container, protected from light, in a cool, dry place.

Structure and conformation

Rutile and anastase crystals are tetragonal. Rutile crystals have greater coverage due to the close packing orientation of the atoms in the crystal. The refractive indices for anatase and rutile crystals are 2.55 and 2.71, respectively. The resultant opacity is due to the light scattering ability of the TiO2. Light, heat, and chemical stability are excellent when employing this material. Additionally, in the United States, TiO2 is regarded as a Category I sunscreen.

Forms and nomenclature

Titanium dioxide occurs in nature in three polymorphic crystal forms: anatase, rutile, and brookite. Moreover, under high pressure, the structure of all three polymorphs of titanium dioxide may be converted into that of α-PbO2. The following diagram summarises the main properties of these three polymorphisms:

Incompatibilities

Titanium dioxide is incompatible with strong oxidizers and strong acids. Violent or incandescent reactions may occur with metals (e.g., aluminum, calcium, magnesium, potassium, sodium, zinc, and lithium).

Incompatibilities

Owing to a photocatalytic effect, titanium dioxide may interact with certain active substances, e.g. famotidine. Studies have shown that titanium dioxide monatonically degrades film mechanical properties and increases water vapor permeability of polyvinyl alcohol coatings when used as an inert filler and whitener.
Titanium dioxide has also been shown to induce photooxidation of unsaturated lipids.

Waste Disposal

Land fill.

Regulatory Status

Accepted as a food additive in Europe. Included in the FDA Inactive Ingredients Database (dental paste; intrauterine suppositories; ophthalmic preparations; oral capsules, suspensions, tablets; topical and transdermal preparations). Included in nonparenteral medicines licensed in the UK. Included in the Canadian List of Acceptable Non-medicinal Ingredients.