TITANIUM OXIDE (IV): STRUCTURE, PROPERTIES, USES - CHEMISTRY - 2025

The titanium oxide (IV) is a solid inorganic crystalline white whose chemical formula is TiO ₂, so 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, pure TiO ₂ is used as a white pigment.

Among its characteristics we can highlight that the solubility of TiO ₂ 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 and titanium oxide), rutile and anatase.

Titanium dioxide powder. The original uploader was Walkerma at English Wikipedia.

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 ultraviolet (UV) absorption are required. For example, as a component of sunscreen for the skin. In these, the TiO ₂ 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, has established 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 deposit in the lungs.

Structure

TiO ₂ 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 ₂ units per cell. Titanium is octahedrally coordinated. Rutile has been shown by calorimetric studies to be the most thermally stable crystalline form.

Rutile crystal structure. Gray balls: Titanium, Pink balls: Oxygen. Solid State Source: Wikipedia Commons

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 ₂ for each crystalline cell.

Crystal structure of anatase. Benjah-bmm27 Source: Wikipedia Commons

Brookite

It crystallizes in the orthorhombic system, with 8 TiO ₂ units 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 ° C.

Anatase: on heating it becomes rutile.

Density

Rutile: 4,250 g / cm ³

Anatase: 4.133 g / cm ³

Brookite: 3,895 g / cm ³

Solubility

Insoluble in water and organic solvents. Dissolves slowly in HF and hot concentrated H ₂ SO ₄. Insoluble in HCl and HNO ₃.

pH

7.5.

Refractive index

Rutile: 2.75 at 550 nm.

Anatase: 2.54 at 550 nm.

It has the highest refractive index of all inorganic pigments.

Other properties

Anatase rapidly converts to rutile at temperatures above 700ºC. TiO ₂ that has been calcined at 900 ° C 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

-Brookita

-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 its chemical inertness.

Source: Pexels.com

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

In plastics, TiO ₂ 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 ₂ 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 threads and the guides generates static electricity. To dissipate it, the TiO ₂ must be burned at 1300 ºC, in order for it to have greater electrical conductivity.

Other applications include the pigmentation of printing inks, rubber, textiles, leather, synthetic fibers, ceramics, white cement, floor covering and roofing materials. As a paper coating, TiO ₂ 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. It is also used in the oxygen sensor of the motor vehicle exhaust system.

Ultrafine TiO ₂ 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 ₂ nanoparticles 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