Iron oxide

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Iron oxide pigment

Altogether there are sixteen known iron oxides and oxyhydroxides.

Oxides

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

Hydroxides

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

Oxide-hydroxides

• goethite (α-FeOOH),
• akaganéite (β-FeOOH),
• lepidocrocite (γ-FeOOH),
• feroxyhyte (δ-FeOOH),
• ferrihydrite (Fe₅HO₈·4H₂O approx.)
• high-pressure FeOOH
• schwertmannite
• green rusts Fe^III_xFe^II_y(OH)_3x+2y-z(A^-)_z; where A^- is Cl^- or 0.5SO₄^2-

Uses

Some iron oxides are widely used in ceramic applications, particularly in glazing. Many metal oxides provide the colors in glazes after being fired at high temperatures.

Iron oxides yield pigments (see Iron oxide pigments). Natural iron oxides pigments are called ochers. Many classic paint colors, such as raw and burnt siennas and umbers, are iron-oxide pigments. These pigments have been used in art since the earliest prehistoric art known, the cave paintings at Lascaux and nearby sites. Iron (III) oxide is typically used.

Iron pigments are also widely used in the cosmetic field. They are considered to be nontoxic, moisture resistant, and nonbleeding. Iron oxides graded safe for cosmetic use are produced synthetically in order to avoid the inclusion of ferrous or ferric oxides, and impurities normally found in naturally occurring iron oxides. Typically, the Iron(II) oxide pigment is black, while the Iron(III) oxide is red or rust-colored. (Iron compounds other than oxides can be other colors.)

Magnetite (under the name Black Oxide) is used for coating steel tools . This protects them from corrosion and gives a pleasing appearance. A grade of hematite called MIO (micaceous iron oxide) is used as anti-corrosion paint (many bridges, Eiffel tower).

Iron oxides are used as contrast agent in Magnetic Resonance Imaging, to shorten proton relaxation times, (T1, T2 and T2*). The superparamagnetic contrast agents are composed of a water insoluble crystalline magnetic core, usually magnetite (Fe3O4) or maghemite (γ-Fe2O3). The mean core diameter ranges from 4 to 10 nm. This crystalline core is often surrounded by a layer of dextran or starch derivatives. The total size of the particle is expressed as the mean hydrated particle diameter. USPIO, Ultrasmall Superparamagnetic Iron Oxide nanoparticles, which usually have single crystal cores, have a mean hydrated particle diameter less than 50 nm.

Properties

• Iron(II) oxide (FeO) or ferrous oxide is also known as wüstite in its mineral form. As a powder this black oxide can cause explosions as it readily ignites.

• Iron(III) oxide (Fe₂O₃) or ferric oxide is also known as hematite (alpha form) or maghemite (gamma form) in its mineral form. As an industrial chemical it is commonly called rouge. Purified, it is used as a coating in magnetic audio and computer media. In a dry or alkaline environment it can cause passivation and inhibits rust, yet it is also a major component of rust.

• Iron(II,III) oxide (Fe₃O₄) or ferrous ferric oxide is also known as magnetite or lodestone in its mineral form, a major iron ore. Magnetite forms readily when iron oxidizes underwater, and so is often found inside tanks or below the waterline of ships.

It is not difficult to extract iron from ore as compared with the similarly abundant elements aluminium and titanium.

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/

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