Iron oxides are chemical compounds composed of iron and oxygen. Several iron

oxide An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...

s are recognized. All are black magnetic solids. Often they are

non-stoichiometric In chemistry, non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having elemental composition whose proportions cannot be represented by a ratio of small natural numbers (i.e. an empirical formula); mos ...

Oxyhydroxide Iron(III) oxide-hydroxide or ferric oxyhydroxideA. L. Mackay (1960): "β-Ferric Oxyhydroxide". ''Mineralogical Magazine'' (''Journal of the Mineralogical Society''), volume 32, issue 250, pages 545-557. is the chemical compound of iron, oxygen, ...

s are a related class of compounds, perhaps the best known of which is rust. Iron oxides and oxyhydroxides are widespread in nature and play an important role in many geological and biological processes. They are used as

iron ore Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the fo ...

s, pigments, catalysts, and in thermite, and occur in hemoglobin. Iron oxides are inexpensive and durable pigments in paints, coatings and colored concretes. Colors commonly available are in the "earthy" end of the yellow/orange/red/brown/black range. When used as a food coloring, it has

E number E numbers ("E" stands for "Europe") are codes for substances used as food additives, including those found naturally in many foods such as vitamin C, for use within the European Union (EU) and European Free Trade Association (EFTA). Commonly ...

E172.

Stoichiometries

Iron oxides feature as ferrous (

Fe(II) In chemistry, iron(II) refers to the element iron in its +2 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe2+. The adjective ferrous or the prefix ferro- is often used to spe ...

) or ferric ( Fe(III)) or both. They adopt octahedral or tetrahedral coordination geometry. Only a few oxides are significant at the earth's surface, particularly wüstite, magnetite, and

hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...

. * Oxides of Fe^II ** FeO: iron(II) oxide, wüstite * Mixed oxides of Fe^II and Fe^III ** Fe₃O₄:

Iron(II,III) oxide Iron(II,III) oxide is the chemical compound with formula Fe3O4. It occurs in nature as the mineral magnetite. It is one of a number of iron oxides, the others being iron(II) oxide (FeO), which is rare, and iron(III) oxide (Fe2O3) which also occur ...

, magnetite ** Fe₄O₅ ** Fe₅O₆ ** Fe₅O₇ ** Fe₂₅O₃₂ **Fe₁₃O₁₉ * Oxide of Fe^III ** Fe₂O₃:

iron(III) oxide Iron(III) oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron(II) oxide (FeO), which is rare; and iron(II,III) oxide (Fe3O4), which also occurs naturally ...

*** α-Fe₂O₃: alpha phase,

*** β-Fe₂O₃: beta phase *** γ-Fe₂O₃: gamma phase, maghemite *** ε-Fe₂O₃: epsilon phase

Thermal expansion

Oxide-hydroxides

* goethite (α-FeOOH), * akaganéite (β-FeOOH), * lepidocrocite (γ-FeOOH), *

feroxyhyte Feroxyhyte is an oxide/hydroxide of iron, δ-Fe3+O(OH). Feroxyhyte crystallizes in the hexagonal system. It forms as brown rounded to concretionary masses. Feroxyhyte is opaque, magnetic, has a yellow streak, and has a relative density of 4.2. ...

(δ-FeOOH), *

ferrihydrite Ferrihydrite (Fh) is a widespread hydrous ferric oxyhydroxide mineral at the Earth's surface, and a likely constituent in extraterrestrial materials. It forms in several types of environments, from freshwater to marine systems, aquifers to hydro ...

(Fe₅HO₈ · 4 H₂O approx., or 5 Fe₂O₃ · 9 H₂O, better recast as FeOOH · 0.4 H₂O) * high-pressure pyrite-structured FeOOH. Once dehydration is triggered, this phase may form FeO₂H_''x'' (0 < ''x'' < 1). * green rust (FeFeOH_{3''x'' + ''y'' − ''z''} (A⁻)_''z'' where A⁻ is Cl⁻ or 0.5 )

Reactions

blast furnaces A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally pig iron, but also others such as lead or copper. ''Blast'' refers to the combustion air being "forced" or supplied above atmospheric p ...

and related factories, iron oxides are converted to the metal. Typical reducing agents are various forms of carbon. A representative reaction starts with ferric oxide: :

In nature

Iron is stored in many organisms in the form of ferritin, which is a ferrous oxide encased in a solubilizing protein sheath. Species of bacteria, including ''

Shewanella oneidensis ''Shewanella oneidensis'' is a bacterium notable for its ability to reduce metal ions and live in environments with or without oxygen. This proteobacterium was first isolated from Lake Oneida, NY in 1988, hence its name. ''S. oneidensis'' is a ...

'', ''

Geobacter sulfurreducens ''Geobacter sulfurreducens'' is a gram-negative metal and sulphur-reducing proteobacterium. It is rod-shaped, obligately anaerobic, non-fermentative, has flagellum and type four pili, and is closely related to ''Geobacter metallireducens''. ''G ...

'' and ''

Geobacter metallireducens ''Geobacter metallireducens'' is a gram-negative metal-reducing proteobacterium. It is a strict anaerobe that oxidizes several short-chain fatty acids, alcohols, and monoaromatic compounds with Fe(III) as the sole electron acceptor. It can als ...

'', use iron oxides as terminal electron acceptors.

Uses

Almost all iron ores are oxides, so in that sense these materials are important precursors to iron metal and its many alloys. Iron oxides are important pigments, coming in a variety of colors (black, red, yellow). Among their many advantages, they are inexpensive, strongly colored, and nontoxic. Magnetite is a component of magnetic recording tapes.

References

External links

Information from Nano-Oxides, Inc. on Fe₂O₃.

Iron Oxide Pigments Statistics and Information

{{Authority control Iron compounds Iron oxide pigments Transition metal oxides