Titanium (IV) oxide structure, properties, uses

The titanium (IV) oxide is a white crystalline inorganic solid whose chemical formula is TiO_two, which is why it is also known as titanium dioxide. It exists in three crystalline forms: rutile, anatase, and brookite. Although in nature it is usually colored due to the presence of impurities such as iron, chromium or vanadium, TiO_two pure is used as white pigment.

Among its characteristics we can highlight that the solubility of TiO_two it depends considerably on its chemical and thermal history. As well as that when it is heated to high temperatures (900 ºC) it becomes chemically inert. Its most important sources are ilmenite (iron titanium oxide), rutile and anatase.

It is produced primarily in a grade suitable for use as a pigment, ensuring its excellent light scattering properties in applications requiring white opacity and gloss..

It is also produced as an ultra-thin material, for applications where transparency and maximum absorption of ultraviolet (UV) rays are required. For example, as a component of sunscreen for the skin. In these, the TiO_two acts as a filter, thus blocking the absorption of these rays.

Due to its chemical inertness, it is the preferred white pigment. However, the United States Food and Drug Administration, or FDA U.S. Food and Drug Administration), has established the parameters for its safe use in food and cosmetics.

There is also a limit on exposure to titanium oxide dust, since when the dust is inhaled, it can be deposited in the lungs..

Article index

• 1 Structure
  • 1.1 Rutile
  • 1.2 Anatase
  • 1.3 Brookite
• 2 Properties
  • 2.1 Physical state
  • 2.2 Mohs hardness
  • 2.3 Molecular weight
  • 2.4 Melting point
  • 2.5 Density
  • 2.6 Solubility
  • 2.7 pH
  • 2.8 Refractive index
  • 2.9 Other properties
• 3 Nomenclature
• 4 Uses
  • 4.1 White pigments
  • 4.2 Plastics
  • 4.3 Other uses
• 5 References

Structure

The uncle_two It has three crystalline modifications: rutile, anatase, and brookite. These crystalline varieties are all found in nature.

Rutile

Rutile crystallizes in the tetragonal system with two TiO units_two for each cell. Titanium is octahedrally coordinated. Rutile has been shown by calorimetric studies to be the most thermally stable crystalline form..

Anatase

This form also crystallizes in the tetragonal system, but anatase occurs in the form of highly distorted octahedra of oxygen atoms with respect to each titanium atom, two of them being relatively closer. It has 4 units of TiO_two for each crystalline cell.

Brookite

Crystallizes in the orthorhombic system, with 8 TiO units_two for each crystalline cell.

Properties

Physical state

Crystalline solid.

Mohs hardness

Rutile: 7-7.5.

Anatase: 5.5-6.

Molecular weight

79.87 g / mol.

Melting point

Rutile: 1830-1850 ºC.

Anatase: on heating it becomes rutile.

Density

Rutile: 4,250 g / cm³

Anatase: 4.133 g / cm³

Brookite: 3.895 g / cm³

Solubility

Insoluble in water and organic solvents. Dissolves slowly in HF and H_twoSW₄ hot concentrate. Insoluble in HCl and HNO₃.

pH

7.5.

Refractive index

Rutile: 2.75 at 550 nm.

Anatase: 2.54 at 550 nm.

Has the highest refractive index of all inorganic pigments.

Other properties

Anatase rapidly converts to rutile at temperatures above 700ºC. The uncle_two that has been calcined at 900 ºC, it dissolves weakly in bases, hydrofluoric acid and hot sulfuric acid. It is not attacked by weak inorganic acids or organic acids. It is not easily reduced or oxidized.

Anatase and rutile are broadband semiconductors, but their electrical conductivity depends on the presence of impurities and defects in the crystal..

Nomenclature

-Titanium dioxide

-Rutile

-Anatase

-Brookite

-Titania

Applications

White pigments

Titanium (IV) oxide's most important use is as a white pigment in a wide variety of products, including paints, lacquers, adhesives, plastics, paper, and printing inks. This is due to its high refractive index and chemical inertness..

The titanium dioxide used as the white pigment must be of high purity. Its opacity and brightness derive from its ability to scatter light. It is brighter than diamond. Only rutile and anatase have good pigmentation properties. 

Plastics

TiO in plastics_two minimizes brittleness and cracking that can occur as a result of exposure to light.

It is the most important pigment in the manufacture of outdoor PVC plastic articles, because it provides UV protection to the material.

The optimal crystalline form in this case is rutile. In this application, the rutile must have a surface coating of zirconium, silica or aluminum, to minimize the photocatalytic effect of TiO._two in the degradation of PVC.

Other uses

Other uses include vitreous enamels used on steel and cast iron, to which it imparts opacity and resistance to acids..

In the textile industry it is used in yarn guides, so that they slide easily during spinning. The friction between the wires and the guides generates static electricity. To dissipate it, TiO_two It must be burned at 1300 ºC, in order to have a higher electrical conductivity.

Other applications include pigmentation of printing inks, rubber, textiles, leather, synthetic fibers, ceramics, white cement, floor covering and roofing materials. As a paper coating, TiO_two makes it whiter, brighter and more opaque.

It is used in cosmetics to help cover skin imperfections, as well as to make toothpaste and soap white..

It protects food, beverages, supplements and pharmaceutical products from premature degradation caused by the effect of light, extending the life of the product.

It is a component in the production of glass, ceramics and electroceramics. It is used in elements of electrical circuits. Also used in motor vehicle exhaust system oxygen sensor.

The uncle_two Ultrafine is used as a component of sunscreen, as it is a strong absorber of ultraviolet (UV) rays, both UV-A and UV-B. UV-A rays cause wrinkles and skin aging, and UV-B cause burns and erythema.

TiO nanoparticles_two are used as support material for chemical reaction catalysts.

Anatase is an effective photocatalyst that oxidizes organic compounds. The smaller its particles, the more effective it is.

References

1. Cotton, F. Albert and Wilkinson, Geoffrey. (1980). Advanced Inorganic Chemistry. John Wiley & Sons.
2. Kirk-Othmer (1994). Encyclopedia of Chemical Technology. Volume 19 and 24. Fourth Edition. John Wiley & Sons.
3. Chemical Safety Facts. (2019). Titanium Dioxide. Recovered from: chemicalsafetyfacts.org
4. Wypych, George. (2015). PVC Additives. In PVC Formulary (Second Edition). Recovered from sciencedirect.com
5. Denning, R. (2009). Enhancing wool products using nanotechnology. In Advances in Wool Technology. Recovered from sciencedirect.com
6. National Library of Medicine. (2019). Titanium Dioxide. Recovered from: pubchem.ncbi.nlm.nih.gov