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An iron oxide is a chemical compound composed of iron and oxygen. Several iron oxides are recognized. Often they are non-stoichiometric. Ferric oxyhydroxides 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 ores, pigments,
Iron oxides feature as
Information from 4thNano-Oxides, Inc. on Fe2O3.
Iron Oxide Pigments Statistics and Information
{{Authority control Iron compounds Iron oxide pigments Transition metal oxides
An iron oxide is a chemical compound composed of iron and oxygen. Several iron oxides are recognized. Often they are non-stoichiometric. Ferric oxyhydroxides 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 ores, pigments, catalysts
Catalysis () is the increase in reaction rate, rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst ...
, 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, short for Europe numbers, 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
In chemistry, iron(II) refers to the chemical element, element iron in its +2 oxidation number, oxidation state. The adjective ''ferrous'' or the prefix ''ferro-'' is often used to specify such compounds, as in ''ferrous chloride'' for iron(II ...
( Fe(II)) 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.
* Oxides of FeII
** FeO: iron(II) oxide, wüstite
* Mixed oxides of FeII and FeIII
** Fe3O4: Iron(II,III) oxide, magnetite
** Fe4O5
** Fe5O6
** Fe5O7
** Fe25O32
**Fe13O19
* Oxides of FeIII
** Fe2O3: iron(III) oxide
*** α-Fe2O3: alpha phase, hematite
*** 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 (δ-FeOOH) * ferrihydrite (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 (FeFeOH3''x'' + ''y'' − ''z'' (A−)''z'' where A− is Cl− or 0.5 )Reactions
In blast furnaces 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 ofbacteria
Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...
, including '' Shewanella oneidensis'', '' Geobacter sulfurreducens'' and '' Geobacter metallireducens'', 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.See also
* Great Oxidation Event * Iron cycle * Iron oxide nanoparticle * Limonite * List of inorganic pigments * Iron(II) hydroxideReferences
External links
Information from 4thNano-Oxides, Inc. on Fe2O3.
Iron Oxide Pigments Statistics and Information
{{Authority control Iron compounds Iron oxide pigments Transition metal oxides