Altogether there are sixteen known iron oxides and oxyhydroxides.[1]
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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 ochres. 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.)
Black oxide converts ferrous materials into magnetite for corrosion resistance purposes. 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.
They may also be used in electrochromic paints.
It is not difficult to extract iron from ore as compared with the similarly abundant elements aluminium and titanium.