Iron oxide

Iron oxide pigment

Role of iron oxides

Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.

Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g., as iron ores, pigments, catalysts, in thermite (see the diagram). Common rust is a form of iron(III) oxide. Iron oxides are widely used as inexpensive, durable pigments in paints, coatings and colored concretes. Colors commonly available are in the "earthy" end of the yellow/orange/red/brown/black range.

Oxides

• iron(II) oxide, wüstite (FeO)
• iron(II,III) oxide, magnetite (Fe₃O₄)
• iron(III) oxide (Fe₂O₃)
  • alpha phase, hematite (α-Fe₂O₃)
  • beta phase, (β-Fe₂O₃)
  • gamma phase, maghemite (γ-Fe₂O₃)
  • epsilon phase, (ε-Fe₂O₃)

Hydroxides

• iron(II) hydroxide (Fe(OH)₂)
• iron(III) hydroxide (Fe(OH)₃), (bernalite)

Oxide/hydroxides

Main article: iron(III) oxide-hydroxide

• goethite (α-FeOOH),
• akaganéite (β-FeOOH),
• lepidocrocite (γ-FeOOH),
• feroxyhyte (δ-FeOOH),
• ferrihydrite (Fe₅HO₈·4H₂O approx.), or 5Fe₂O₃•9H₂O, better recast as FeOOH•0.4H₂O

• high-pressure FeOOH
• schwertmannite (ideally Fe₈O₈(OH)₆(SO)·nH₂O or Fe³⁺₁₆O₁₆(OH,SO₄)_12-13·10-12H₂O)
• green rusts (Fe^III_xFe^II_y(OH)_3x+2y-z(A^-)_z; where A^- is Cl^- or 0.5SO₄^2-)

See also

• Limonite
• Iron oxide nanoparticles

External links

• Information from Nano-Oxides, Inc. on Fe₂O₃.
• http://chemed.chem.purdue.edu/demos/demosheets/12.3.html
• http://minerals.usgs.gov/minerals/pubs/commodity/iron_oxide/