Iron (III) oxide structure, nomenclature, properties, uses

The iron (III) oxide Ferric oxide is an inorganic solid formed by the reaction of iron (Fe) and oxygen (O_two), in which an iron oxidation state of +3 is obtained. Its chemical formula is Fe_twoOR₃.

In nature it is found mainly in the form of the mineral hematite, which owes its name to the red color of its stripes. Hematite is the main iron ore for industrial use.

The color and appearance of Fe_twoOR₃ they depend on the size and shape of its particles, as well as the identity and amount of impurities and water present. The yellow, orange and red pigments are known. Does not have metallic shine.

It does not conduct electricity, but mixed with other oxides it can make semiconductor glasses. The alpha crystalline form is antiferromagnetic and the gamma is ferromagnetic.

It is used as a red pigment in paints, rubbers, ceramics and paper. Also in protective coatings for steel and other metals. Its versatility is due to its dyeability and coating power, its resistance to ultraviolet light and alkalis..

It is used in the preparation of garnets or fine stones of various metallic oxides. It is used to polish glass, diamond and precious metals (jewelry grade). It is also used as a catalyst in various reactions. It has been used for wastewater treatment.

Article index

• 1 Structure
  • 1.1 Alpha
  • 1.2 Gamma
  • 1.3 Beta and Epsilon:
• 2 Nomenclature
• 3 Properties
  • 3.1 Physical state
  • 3.2 Molecular weight
  • 3.3 Melting point
  • 3.4 Density
  • 3.5 Solubility
  • 3.6 Other properties
• 4 Uses
  • 4.1 In the construction industry
  • 4.2 In paints and coatings
  • 4.3 In the plastics and rubber industry
  • 4.4 In glass and jewelry
  • 4.5 On magnetic recording material
  • 4.6 In the food, pharmaceutical and cosmetic industry
  • 4.7 In catalysis of chemical reactions
  • 4.8 In reducing global warming
  • 4.9 Other uses
• 5 References

Structure

Alpha

The crystalline form α-Fe_twoOR₃ has the structure of corundum (mineral Al_twoOR₃), where oxide ions (O^-two) form hexagonal packed layers, with Fe ions⁺³ occupying two-thirds of the octahedral sites.

In other words, each Faith⁺³ is octahedrally surrounded by 6 O ions^-two. Its color changes with increasing particle size from bright red to dark purple.

Gamma

Γ-Fe_twoOR₃ presents a spinel-like structure with a cubic packing arrangement of oxide ions, with Fe ions⁺³ randomly distributed between the octahedral and tetrahedral interstices. This crystalline variety, when heated in air at more than 400 ºC, changes to the alpha structure. It has a brown color.

Beta and Epsilon:

They are rare crystalline forms of this oxide. Β-Fe_twoOR₃ crystallizes into a rhombohedral system. This structure is metastable and when heated above approximately 500 ºC it changes to the alpha variety..

The ε-Fe_twoOR₃ crystallizes orthorhombic. It is also metastable and at temperatures between 230 and 500 ºC it passes into the alpha structure..

Nomenclature

Hematite: natural mineral Fe_twoOR₃ which crystallizes in the alpha form. It is also known as specularite or oligisto.

Maghemite or magnetic hematite: gamma form of Fe_twoOR₃, little abundant in nature.

Ferric oxide: Faith_twoOR_3.

Natural iron (III) oxides: They are those found in nature. They were used since prehistoric times, for example, in the paintings of the Altamira caves.

Synthetic iron (III) oxides: they are prepared synthetically, obtaining a composition that corresponds to that of natural minerals. They are preferred over naturals for their sheer hue or hue, consistent properties, and tinting ability..

Properties

Physical state

Solid, whose coloration can be luminous red, reddish brown and dark violet depending on the crystalline structure and the particle size.

Molecular weight

159.69 g / mol.

Melting point

1566 ºC.

Density

5.24 g / cm³

Solubility

Insoluble in water, soluble in hydrochloric acid (HCl) and sulfuric acid (H_twoSW₄).

Other properties

- Iron (III) oxides are characterized by their low color intensity, their excellent resistance to ultraviolet light, their dyeability and excellent covering power..

- They are non-toxic, colorfast and inexpensive.

- They are resistant to alkalis. They do not react with weak acids or weak bases. If they are not contaminated with manganese (Mn), they do not react with organic solvents.

- The alpha form is either paramagnetic (it is attracted to magnets, but does not become a permanently magnetized material) or antiferromagnetic. It is electrical insulator.

- The gamma form is ferromagnetic. This means that when subjected to a magnetic field, the material's magnetic dipoles are arranged, which remains for a certain time after eliminating the magnetic field..

Applications

In the construction industry

Iron (III) oxide pigments are largely used to color cement and other construction materials: concrete tiles, paving bricks, fibrous cement, bitumen or mortar, among others..

This use is based on the fact that they do not affect the setting time, the compression force, or the tensile strength of cement or other materials..

Can be incorporated into many binders due to their pure color hue, good covering power, good abrasion resistance and low tendency to sediment.

In paints and coatings

Due to their resistance to acids and bases, they are used as pigments in paints and varnishes. Their resistance to high temperatures makes them good in enamels.

Synthetic hematite-based pigments are used in corrosion protection coatings, especially marine ones. Its crystalline structure delays the penetration of moisture and corrosive substances present in the saltpeter.

Protects well on coatings for interiors, exteriors and metal parts. In the maintenance and repainting of bridges, its use leads to protection against humidity, dew or dense fog, and to easy drying at low ambient temperatures.

Also used in wallcovering paper.

In the plastics and rubber industry

Iron (III) oxides are used to color plastics and rubbers. Synthetic iron (III) oxides are preferred in this application. Although natural iron (III) oxides are cheaper, their use has decreased compared to synthetics.

In glass and jewelry

They are also used in polishing glass, precious metals, diamonds and precious stones..

They also serve as colorants in the manufacture of glasses.

On magnetic recording material

The gamma form has been used as a magnetic material in the production of magnetic recording media, for example, in information storage systems such as audio and video cassettes, in broadcast studios, floppy disks, computer tapes, and computer hard or soft drives..

In such an application, the particle size is extremely important to ensure good magnetic properties. The noise level in magnetic tapes decreases as the particle size decreases.

Their resistance to friction is also important, since floppy disks have a magnetic layer where maghemite particles are found, and their useful use time depends on the ability of said layer to withstand friction..

Magnetic polymeric compounds have been prepared with nanoparticles of γ-Fe_twoOR₃, for use in electromagnetic interference and microwave absorption devices.

In the food, pharmaceutical and cosmetic industry

Pigments based on synthetic iron (III) oxides that have been produced from pure starting materials are considered non-toxic..

For this reason they can be used as colorants in food, pharmaceutical and cosmetic products..

In catalysis of chemical reactions

Iron (III) oxides are used as catalysts or catalyst bases in various chemical processes.

Together with cellulose acetate, they have been tested as a support for metal nanoparticles to be used as catalysts in the degradation of toxic organic compounds that pollute wastewater.

Due to their ability to absorb light from the visible spectrum, they have been proposed for photocatalysis in the photodegradation of organic pollution..

In reducing global warming

Hematite has been studied as a sorbent in carbon dioxide (CO_two). It is being investigated if this would help to solve the problem of the effects of global warming produced by the high concentration of CO_two in the atmosphere.

Other uses

- Due to its adsorptive capacity, Fe_twoOR₃ It is used in the manufacture of fluorine or other gas sensors, and in humidity detectors.

- Mixed with other oxides, it is used in the production of semiconductor crystals..

- It has been used as an enhancer of the electrochemical properties in rechargeable lithium batteries..

References

1. American Elements (2019). Iron (III) Oxide. Recovered from americanelements.com.
2. Cotton, F. Albert and Wilkinson, Geoffrey. (1980). Advanced Inorganic Chemistry. John Wiley & Sons.
3. Kirk-Othmer (1994). Encyclopedia of Chemical Technology. Volume 14 and 19. Fourth Edition. John Wiley & Sons.
4. Ullmann's Encyclopedia of Industrial Chemistry. (1990). Volume A20. Fifth Edition. VCH. Verlagsgessellschaft mbH.
5. Castaño, J.G. and Arroyave, C. (1998). The functionality of iron oxides. Metal. Madrid, 34 (3), 1998. Recovered from revistademetalurgia.revistas.csic.es
6. Esraa M. Bakhsh, Shahid Ali Khan, Hadi M. Marwani, Ekram Y. Danish, Abdullah M. Asiri, Sher Bahadar Khan. (2017). Performance of cellulose acetate-ferric oxide nanocomposite supported metal catalysts toward the reduction of environmental pollutants. International Journal of Biological Macromolecules. DOI: 10.1016 / j.ijbiomac.2017.09.034
7. Mora Mendoza, E.Y. et al. (2019). Iron oxides as efficient sorbents for CO2 capture. Journal of Materials Research and Technology. 2019, 8 (3): 2944-2956. Recovered from sciencedirect.com.
8. Piao Xu, et al. (2012). Use of iron oxide nanomaterials in wastewater treatment: A review. Science of the Total Environment 424 (2012) 1-10. Recovered from sciencedirect.com.