Титана диоксид

Описание

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.

Химические свойства

Ttitanium dioxide is an odorless white powder.

Физические свойства

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.

Физические свойства

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.

Вхождение

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.

Использование

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.

Подготовка

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.

Методы производства

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.

Общее описание

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.

Опасность

Lower respiratory tract irritant. Possible carcinogen.

Угроза здоровью

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

Фармацевтические приложения

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.

Профиль безопасности

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.

Безопасность

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

Возможный контакт

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.

Канцерогенность

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.

хранилище

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.

Формы и номенклатура

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:

Несовместимости

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).

Утилизация отходов

Land fill.

Регуляторный статус

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.