Iron (II) oxide

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Crystal structure
Structure of iron (II) oxide
__ Fe 2+      __ O 2−
Surname Iron (II) oxide
other names
  • Iron oxide
  • Iron monoxide
  • Wustite (mineral)
Ratio formula FeO
Brief description

black powder

External identifiers / databases
CAS number 1345-25-1
EC number 215-721-8
ECHA InfoCard 100.014.292
PubChem 14945
ChemSpider 14237
Wikidata Q196680
Molar mass 71.85 g mol −1
Physical state



5.75 g cm −3

Melting point

1369 ° C


almost insoluble in water

safety instructions
GHS labeling of hazardous substances
02 - Highly / extremely flammable


H and P phrases H: 228
P: 210

1.5 mg m −3

As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Iron (II) oxide (formerly also called iron oxide ) is a chemical compound of iron and oxygen and is one of the oxides . Iron (II) oxide is normally not built up stoichiometrically , the composition is around Fe 0.84 O to Fe 0.95 O. The reason for this is the similar crystal structure of iron (III) oxide and that crystal defects are entropically favorable.


Iron (II) oxide occurs during the fresh process / LD process (lowering the carbon content ) in steel production . Here, oxygen is blown into the iron melt. The oxygen combines with iron to form FeO, which in turn acts as an oxidizing agent for interfering foreign elements such as silicon , manganese and phosphorus :

With the help of calcium oxide (CaO) these oxides can be separated from the iron melt.

In nature, iron (II) oxide occurs as a mineral wüstite .

Extraction and presentation

Iron (II) oxide is formed during the reduction of iron (III) oxide with hydrogen or carbon monoxide . Iron (II) oxide can also be obtained by oxidizing iron under low oxygen pressure or with water vapor at temperatures above 560 ° C.

Stoichiometric iron (II) oxide can be produced by heating iron (II) oxalate to around 850 ° C in a vacuum and then quickly quenching it to room temperature.

Furthermore, stoichiometric iron (II) oxide is formed in the reaction of Fe 1-x O and iron at 770 ° C. and 50 kbar oxygen pressure.


Iron (II) oxide is only stable above 560 ° C. Below this temperature down to approx. 300 ° C it tends to disproportionate to iron and iron (II, III) oxide :

It is metastable at room temperature . It can be easily oxidized; finely divided FeO obtained from the oxalate by pyrolysis is pyrophoric .

Iron (II) oxide antiferromagnetic with a Néel temperature of 198  K .

Individual evidence

  1. Entry on CI 77489 in the CosIng database of the EU Commission, accessed on February 26, 2020.
  2. a b c d e Entry for CAS no. 1345-25-1 in the GESTIS substance database of the IFA , accessed on August 1, 2007 (JavaScript required)
  3. a b Data sheet Iron (II) oxide at Sigma-Aldrich , accessed on March 29, 2011 ( PDF ).
  4. ^ A b c A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 1652.
  5. a b Georg Brauer (Ed.) U. a .: Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume III, Ferdinand Enke, Stuttgart 1981, ISBN 3-432-87823-0 .