iron(II,III) oxide
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Iron(II,III) oxide is the chemical compound with formula Fe3O4. It occurs in nature as the mineral
magnetite Magnetite is a mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure for ...

magnetite
. It is one of a number of
iron oxides Iron oxides are chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemi ...

iron oxides
, the others being
iron(II) oxide Iron(II) oxide or ferrous oxide is the inorganic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structur ...

iron(II) oxide
(FeO), which is rare, and
iron(III) oxide Iron(III) oxide or ferric oxide is the inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. However, the distinction is ...
(Fe2O3) which also occurs naturally as the mineral
hematite Hematite (), also spelled as haematite, is a common iron oxide Iron oxides are chemical compounds composed of iron and oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member o ...

hematite
. It contains both Fe2+ and Fe3+ ions and is sometimes formulated as FeO ∙ Fe2O3. This iron oxide is encountered in the laboratory as a black powder. It exhibits permanent magnetism and is
ferrimagnetic A ferrimagnetic material is a material that has populations of atoms with opposing magnetic moment The magnetic moment is the magnetic strength and orientation of a or other object that produces a . Examples of objects that have magnetic m ...
, but is sometimes incorrectly described as
ferromagnetic Ferromagnetism is the basic mechanism by which certain materials (such as iron Iron () is a with Fe (from la, ) and 26. It is a that belongs to the and of the . It is, on , right in front of (32.1% and 30.1%, respectively), formi ...
. Its most extensive use is as a black pigment. For this purpose, it is synthesized rather than being extracted from the naturally occurring mineral as the particle size and shape can be varied by the method of production.


Preparation

Under
anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: *Adhesive#Anaerobic, Anaerobic ad ...
conditions,
ferrous hydroxide Iron(II) hydroxide or ferrous hydroxide is an inorganic compound with the formula Fe(OH)2. It is produced when iron(II) salts, from a compound such as iron(II) sulfate, are treated with hydroxide Hydroxide is a polyatomic ion, diatomic anion wi ...
(Fe(OH)2) can be oxidized by water to form magnetite and molecular
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
. This process is described by the
Schikorr reaction The Schikorr reaction formally describes the conversion of the iron(II) hydroxide (Fe(OH)2) into iron(II,III) oxide (Fe3O4). This transformation reaction was first studied by Gerhard Schikorr. The global reaction follows: :\underset -> \underset + ...
: :\underset -> \underset + \underset + \underset The well-crystallized magnetite (Fe3O4) is thermodynamically more stable than the ferrous hydroxide (Fe(OH)2 ). Magnetite can be prepared in the laboratory as a
ferrofluid Ferrofluid is a liquid that is attracted to the poles of a magnet A magnet is a material or object that produces a magnetic field A magnetic field is a vector field In vector calculus and physics, a vector field is an assignmen ...

ferrofluid
in the Massart method by mixing
iron(II) chloride Iron(II) chloride, also known as ferrous chloride, is the chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemic ...

iron(II) chloride
and
iron(III) chloride Iron(III) chloride is the inorganic compound with the formula (). Also called ferric chloride, it is a common compound of iron in the +3 oxidation state The oxidation state, or oxidation number, is the hypothetical charge Charge or charged may r ...
in the presence of
sodium hydroxide Sodium hydroxide, also known as lye A lye is a metal hydroxide traditionally obtained by leaching wood ashes, or a strong alkali In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chem ...

sodium hydroxide
. Magnetite can also be prepared by the chemical co-precipitation in presence of ammonia, which consist in a mixture of a solution 0.1 M of FeCl3·6H2O and FeCl2·4H2O with mechanic agitation of about 2000 rpm. The molar ratio of FeCl3:FeCl2 can be 2:1; heating this solution at 70 °C, and immediately the speed is elevated to 7500 rpm and adding quickly a solution of NH4OH (10 volume %), immediately a dark precipitate will be formed, which consists of nanoparticles of magnetite. In both cases, the precipitation reaction rely on a quick transformation of acidic hydrolyzed iron ions into the spinel iron oxide structure, by hydrolysis at elevated pH values (above ca. 10). Considerable efforts has been devoted towards controlling the particle formation process of magnetite nanoparticles due to the challenging and complex chemistry reactions involved in the phase transformations prior to the formation of the magnetite spinel structure. Magnetite particles are of interests in bioscience applications such as in
magnetic resonance imaging Magnetic resonance imaging (MRI) is a medical imaging Medical imaging is the technique and process of imaging Imaging is the representation or reproduction of an object's form; especially a visual representation (i.e., the formation of a ...
(MRI) since iron oxide magnetite nanoparticles represent a non-toxic alternative to currently employed gadolinium-based
contrast agents A contrast agent (or contrast medium) is a Chemical substance, substance used to increase the Display contrast, contrast of structures or fluids within the body in medical imaging. Contrast agents absorb or alter external electromagnetism or ultras ...
. However, due to lack of control over the specific transformations involved in the formation of the particles, truly superparamagnetic particles have not yet been prepared from magnetite, i.e. magnetite nanoparticles that completely lose their permanent magnetic characteristic in the absence of an external magnetic field (which by definition show a coercivity of 0 A/m). The smallest values currently reported for nanosized magnetite particles is ''Hc'' = 8.5 A m−1, whereas the largest reported magnetization value is 87 Am2 kg−1 for synthetic magnetite. Pigment quality Fe3O4, so called synthetic magnetite, can be prepared using processes that use industrial wastes, scrap iron or solutions containing iron salts (e.g. those produced as by-products in industrial processes such as the acid vat treatment (
pickling Pickling is the process of preserving or extending the shelf life of food Food is any substance consumed to provide Nutrient, nutritional support for an organism. Food is usually of plant, animal or Fungus, fungal origin, and contains ess ...
) of steel): *Oxidation of Fe metal in the Laux process where
nitrobenzene Nitrobenzene is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior ...

nitrobenzene
is treated with iron metal using FeCl2 as a catalyst to produce
aniline Aniline is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior an ...

aniline
: :C6H5NO2 + 3 Fe + 2 H2O → C6H5NH2 + Fe3O4 *Oxidation of FeII compounds, e.g. the precipitation of iron(II) salts as hydroxides followed by oxidation by aeration where careful control of the pH determines the oxide produced. Reduction of Fe2O3 with hydrogen: :3Fe2O3 + H2 → 2Fe3O4 +H2O Reduction of Fe2O3 with CO: :3Fe2O3 + CO → 2Fe3O4 + CO2 Production of nano-particles can be performed chemically by taking for example mixtures of FeII and FeIII salts and mixing them with alkali to precipitate colloidal Fe3O4. The reaction conditions are critical to the process and determine the particle size.


Reactions

Reduction of magnetite ore by in a
blast furnace A blast furnace is a type of metallurgical Metallurgy is a domain of Materials science, materials science and engineering that studies the physical and chemical behavior of metallic Chemical element, elements, their Inter-metallic alloy, inter- ...
is used to produce iron as part of steel production process: : + 4CO -> + 4CO2 Controlled oxidation of Fe3O4 is used to produce brown pigment quality γ-Fe2O3 (
maghemite Maghemite (Fe2O3, γ-Fe2O3) is a member of the family of iron oxide Iron oxides are chemical compounds composed of iron and oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a membe ...
):Gunter Buxbaum, Gerhard Pfaff (2005) ''Industrial Inorganic Pigments'' 3d edition Wiley-VCH :\ce\ More vigorous calcining (roasting in air) gives red pigment quality α-Fe2O3 (
hematite Hematite (), also spelled as haematite, is a common iron oxide Iron oxides are chemical compounds composed of iron and oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member o ...

hematite
): :\ce\


Structure

Fe3O4 has a cubic inverse
spinel group The spinels are any of a class of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs natur ...
structure which consists of a cubic close packed array of oxide ions where all of the Fe2+ ions occupy half of the octahedral sites and the Fe3+ are split evenly across the remaining octahedral sites and the tetrahedral sites. Both
FeO Iron(II) oxide or ferrous oxide is the inorganic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structur ...

FeO
and γ-Fe2O3 have a similar cubic close packed array of oxide ions and this accounts for the ready interchangeability between the three compounds on oxidation and reduction as these reactions entail a relatively small change to the overall structure. Fe3O4 samples can be
non-stoichiometric Non-stoichiometric compounds are chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held t ...
. The
ferrimagnetism A ferrimagnetic material is a material that has populations of atoms with opposing magnetic moments, as in antiferromagnetism. For ferrimagnetic materials, these moments are unequal in magnitude so a spontaneous magnetization remains. This can ...
of Fe3O4 arises because the electron spins of the FeII and FeIII ions in the octahedral sites are coupled and the spins of the FeIII ions in the tetrahedral sites are coupled but anti-parallel to the former. The net effect is that the magnetic contributions of both sets are not balanced and there is a permanent magnetism. In the molten state, experimentally constrained models show that the iron ions are coordinated to 5 oxygen ions on average. There is a distribution of coordination sites in the liquid state, with the majority of both FeII and FeIII being 5-coordinated to oxygen and minority populations of both 4- and 6-fold coordinated iron.


Properties

Fe3O4 is
ferrimagnetic A ferrimagnetic material is a material that has populations of atoms with opposing magnetic moment The magnetic moment is the magnetic strength and orientation of a or other object that produces a . Examples of objects that have magnetic m ...
with a
Curie temperature In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and forc ...
of 858 K. There is a phase transition at 120K, called Verwey transition where there is a discontinuity in the structure, conductivity and magnetic properties. This effect has been extensively investigated and whilst various explanations have been proposed, it does not appear to be fully understood. While it has much higher
electrical resistivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current An electric current is a stream of charged particle In p ...
than iron metal (96.1 nΩ m), Fe3O4's electrical resistivity (0.3 mΩ m ) is significantly lower than that of Fe2O3 (approx kΩ m). This is ascribed to electron exchange between the FeII and FeIII centres in Fe3O4.


Uses

Fe3O4 is used as a black pigment and is known as ''C.I pigment black 11'' (C.I. No.77499) or Mars Black. Fe3O4 is used as a catalyst in the
Haber process The Haber process, also called the Haber–Bosch process, is an artificial nitrogen fixation process and is the main industrial procedure for the ammonia production, production of ammonia today. It is named after its inventors, the German chemist ...

Haber process
and in the
water-gas shift reaction The water-gas shift reaction (WGSR) describes the reaction of carbon monoxide and water vapor (99.9839 °C) , - , Boiling point , , - , specific gas constant , 461.5 J/( kg·K) , - , Heat of vaporization , 2.27 MJ/kg , - , Hea ...
.Sunggyu Lee (2006) Encyclopedia of Chemical Processing CRC Press The latter uses an HTS (high temperature shift catalyst) of iron oxide stabilised by
chromium oxide Chromium oxide may refer to: * Chromium(II) oxide, CrO * Chromium(III) oxide, Cr2O3 * Chromium dioxide (chromium(IV) oxide), CrO2, which includes the hypothetical compound chromium(II) chromate * Chromium trioxide (chromium(VI) oxide), CrO3 * Chrom ...

chromium oxide
. This iron–chrome catalyst is reduced at reactor start up to generate Fe3O4 from α-Fe2O3 and Cr2O3 to CrO3. Bluing is a passivation process that produces a layer of Fe3O4 on the surface of steel to protect it from rust. Ferumoxytol along with sulfur and aluminium, it is an ingredient in a specific type of thermite useful for cutting steel.


Medical uses

Nano particles of Fe3O4 are used as contrast agents in MRI scanning. Ferumoxytol, sold under the brand names Feraheme and Rienso, is an
intravenous Intravenous therapy (abbreviated as IV therapy) is a medical technique that delivers fluids, medications and nutrition directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutrition ...
Fe3O4 preparation for treatment of
anemia Anemia (American and British English spelling differences#ae and oe, also spelled anaemia) is a decrease in the total amount of red blood cells (RBCs) or hemoglobin in the blood, or a lowered ability of the blood to carry oxygen. When anemia c ...

anemia
resulting from
chronic kidney disease Chronic kidney disease (CKD) is a type of kidney disease Kidney disease, or renal disease, technically referred to as nephropathy, is damage to or disease A disease is a particular abnormal condition that negatively affects the str ...
. Ferumoxytol is manufactured and globally distributed by
AMAG Pharmaceuticals AMAG Pharmaceuticals, Inc. is an American pharmaceutical company developing products that treat iron deficiency anemia (IDA) in adult patients. The company was a publicly traded company listed on NASDAQ under the symbol "AMAG" until November 2020 ...
.


Biological occurrence

Magnetite has been found as nano-crystals in
magnetotactic bacteria Magnetotactic bacteria (or MTB) are a polyphyletic 300px, Cladogram of the primates, showing a monophyly (the simians, in yellow), a paraphyly">monophyly.html" ;"title="primates, showing a monophyly">primates, showing a monophyly (the simians, ...
(42–45 nm) and in the beak tissue of
homing pigeon The true messenger pigeon is a variety of domestic pigeons The domestic pigeon (''Columba livia domestica'') is a Columbidae, pigeon subspecies that was derived from the rock dove (also called the rock pigeon). The rock pigeon is the world's ...

homing pigeon
s.


References


External links

* {{Portal bar , Medicine Iron(II,III) compounds Semiconductor materials Iron oxide pigments Non-stoichiometric compounds Excipients