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, 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 E172.
ferrihydrite (Fe5HO8 · 4 H2O approx., or 5 Fe2O3 · 9 H2O, better recast as FeOOH · 0.4 H2O)
high-pressure pyrite-structured FeOOH.[7] Once
dehydration is triggered, this phase may form FeO2Hx (0 < x < 1).[8]
green rust (FeIII xFeII yOH3x + y − z (A−)z where A− is Cl− or 0.5 SO2−4)
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:[9]
2 Fe2O3 + 3 C → 4 Fe + 3 CO2
In nature
Iron is stored in many organisms in the form of
ferritin, which is a ferrous oxide encased in a solubilizing protein sheath.[10]
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.[12]
Magnetite is a component of magnetic recording tapes.
^Merlini, Marco; Hanfland, Michael; Salamat, Ashkan; Petitgirard, Sylvain; Müller, Harald (2015). "The crystal structures of Mg2Fe2C4O13, with tetrahedrally coordinated carbon, and Fe13O19, synthesized at deep mantle conditions". American Mineralogist. 100 (8–9): 2001–2004.
Bibcode:
2015AmMin.100.2001M.
doi:
10.2138/am-2015-5369.
S2CID54496448.
^
abcFakouri Hasanabadi, M.; Kokabi, A.H.; Nemati, A.; Zinatlou Ajabshir, S. (February 2017). "Interactions near the triple-phase boundaries metal/glass/air in planar solid oxide fuel cells". International Journal of Hydrogen Energy. 42 (8): 5306–5314.
doi:
10.1016/j.ijhydene.2017.01.065.
ISSN0360-3199.