IRON (II) OXIDE: STRUCTURE, NOMENCLATURE, PROPERTIES, USES - CHEMISTRY - 2025

The iron oxide (II) oxide or ferrous, is a black inorganic solid formed by the reaction of oxygen (O ₂) with iron (Fe) to the +2 oxidation state. It is also called iron monoxide. Its chemical formula is FeO.

It is found in nature as the mineral wustite, a member of the periclase group. It is also known as wuestite, iosiderite or iozite. Wustite is an opaque mineral, black to brown in color, although under reflected light it is gray. It has a metallic luster.

Ferrous oxide or iron (II) oxide powder. FK1954. Source: Wikipedia Commons

Iron (II) oxide can be obtained by thermal vacuum decomposition of iron (II) oxalate, obtaining a pyrophoric black powder. This powder decreases its state of division and becomes less reactive when heated to high temperatures.

Iron (II) oxide crystals can only be obtained under equilibrium conditions at high temperature, rapidly cooling the system. If the reaction is carried out at lower temperatures, FeO is unstable and becomes iron (Fe) and oxide Fe ₃ O ₄, since slow cooling favors disproportion.

Because it is pyrophoric, it is a material that presents a fire risk. In addition, it is dangerous if inhaled in large amounts and for a long time, as it can cause lung disease.

Iron (II) oxide is used as a pigment in ceramics, enamels, glasses and cosmetics. For its magnetic properties it is used in medicine. It is also used as an antioxidant in packaged foods and, additionally, it is used in reaction catalysis and in pesticide formulas.

Structure

Iron (II) oxide (FeO) theoretically possesses the cubic structure of rock salt, having 4 Fe ²⁺ ions and 4 O ^2- ions for each unit cell, and Fe ²⁺ ions occupying the octahedral sites.

However, the reality is that it deviates significantly from the ideal rock salt structure of FeO, as it is a complex faulty arrangement.

Some Fe ²⁺ ions are replaced by Fe ³⁺ ions, so the crystalline structure is always iron deficient. For this reason it is said to be a non-stoichiometric solid. The formula that best describes it is Fe _1-x O.

On the other hand, hydrated iron (II) oxide (FeO.nH ₂ O) is a green crystalline solid.

Nomenclature

It has several names:

- Iron (II) oxide.

- Ferrous oxide.

- Iron monoxide.

- Wustita.

- Wuestita.

- Iosiderite.

- Iozita.

Properties

Physical state

Crystalline solid.

Mohs hardness

5-5.5.

Molecular weight

71.84 g / mol.

Melting point

1368 ° C.

Density

5.7 g / cm ³

Solubility

Practically insoluble in water and alkalis. Quickly soluble in acids. Insoluble in alcohol.

Refractive index

2.23.

Other properties

- Easily oxidized in air. Under certain conditions it ignites spontaneously in air. That is why it is said to be pyrophoric.

- It is a strong base and absorbs carbon dioxide quickly.

- The natural mineral wustite is highly magnetic. However, below -75 ºC FeO is antiferromagnetic.

- Wustite behaves like a semiconductor.

- The magnetic and electrical conductivity properties, as well as its structure, depend on its thermal history and the pressures to which it has been subjected.

Risks

- Inhalation of iron (II) oxide dust or fumes is considered dangerous, as it can cause irritation of the nose and throat and can affect the lungs.

- High levels of exposure to FeO dust can lead to a condition called metal fume fever, an occupational exposure disease that causes flu-like symptoms.

- Continued exposure to high levels of FeO can have more serious effects, including a disease known as siderosis. This is an inflammation of the lungs that is accompanied by symptoms similar to pneumonia.

Applications

In pottery

FeO has long been used as a pigment in ceramic mixtures.

In glass manufacturing

Due to its green color, hydrated ferrous oxide (FeO.nH ₂ O) excels in green glass manufacture with heat absorbing characteristics. This type of glass is used in buildings, cars, wine bottles, and other applications.

Green glass bottles. Vinitagangurde. Source: Wikipedia Commons

In the steel industry

FeO is used as a raw material in the manufacture of steel. It is important to underline that in this application, the activity of FeO must be controlled, because if it is in excess it can negatively affect the process, especially it can increase the oxidation of aluminum. To avoid this, aluminum or calcium carbide is often added to the slag phase.

In catalysis of chemical reactions

It is used as a catalyst in a large number of industrial and chemical operations. In catalyst preparations, those used in the synthesis of NH ₃ and methanation stand out.

In pesticides

It is used in formulas for home control of insects.

In the cosmetic industry

It is used in cleansers, regenerators, and personal care creams.

As a coloring agent or pigment in cosmetics, it is used to cover imperfections on the surface of the skin. Because it is insoluble in water, when used it remains in the form of crystals or particles and allows greater coating.

Being a mineral pigment, it is more resistant to light than organic colorants. Mineral pigments are more opaque but less shiny. Hydrated iron (II) oxide offers excellent stability and is among the most used mineral pigments in makeup.

In medicine

Magnetic FeO nanoparticles are widely used in this field. For example, pharmaceutical drug targeting and techniques such as cell sorting take advantage of the attraction of magnetic particles to high magnetic flux densities. This applies to cancer treatment.

In food preservation

FeO acts as an antioxidant in food packaging. It is added as a fine powder in a bag or label attached to the packaging, separated from the product. In this way it is released at a controlled rate.

Due to its property of reacting easily with oxygen, it acts as an O ₂ capture agent, reducing its concentration within the packaging where the food is located.

Thus, the oxidative degradation of the food is delayed, increasing its duration. It is used especially in the preservation of meats.

Meat packaging in a supermarket. User: Mattes. Source: Wikipedia Commons

Other uses

The cosmetic industry uses FeO to create pigments in enamels.

References

1. Cotton, F. Albert and Wilkinson, Geoffrey. (1980). Advanced Inorganic Chemistry. Fourth Edition. John Wiley & Sons.
2. S. National Library of Medicine. (2019). Ferrous oxide. Recovered from pubchem.ncbi.nlm.nih.gov.
3. Dance, JC; Emeléus, HJ; Sir Ronald Nyholm and Trotman-Dickenson, AF (1973). Comprehensive Inorganic Chemistry. Volume 3. Pergamon Press.
4. Kirk-Othmer (1994). Encyclopedia of Chemical Technology. Volume 14. Fourth Edition. John Wiley & Sons.
5. Valet, B.; Major M.; Fitoussi, F.; Capellier, R.; Dormoy, M. and Ginestar, J. (2007). Coloring Agents in Decorative and other Cosmetics. Analytical Methods. 141-152. Recovered from sciencedirect.com.
6. Heness, G. (2012). Metal-polymer nanocomposites. Advances in Polymer nanocomposites. Recovered from sciencedirect.com
7. Dalla Rosa, Marco (2019). Packaging Sustainability in the Meat Industry. In Sustainable Meat Production and Processing. Chapter 9. Recovered from sceincedirect.com.
8. Hudson Institute of Mineralogy (2019). Wüstite. Recovered from mindat.org.
9. Hazen, Robert M. and Jeanloz, Raymond (1984). Wüstite (Fe _1-x O): A Review of Its Defect Structure and Physical Properties. Reviews of geophysics and space physics, Vol. 22, No.1, Pages 37-46, February 1984.