Iron(III) phosphate

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Iron(III) phosphate
A-quartz.png Iron(III)-phosphate-pentahydrate-sample.jpg
CAS number (anhydrous) 10045-86-0 (anhydrous)
Appearance yellow solid
Density 3.056 g/cm3
Solubility in water insoluble
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Iron(III) phosphate is the inorganic compound with the formula FePO4. Several related materials are known, including four polymorphs of FePO4 and two polymorphs of the dihydrate FePO4(H2O)2. These materials find several technical applications as well as occurring in the mineral kingdom.[1]


The most common form of FePO4 adopts the structure of α-quartz. As such the P and Fe have tetrahedral molecular geometry. At high pressures, a phase change occurs to a more dense structure with octahedral Fe centres. Two orthorhombic structures and a monoclinic phase are also known. In the two polymorphs of the dihydrate, the Fe center is octahedral with two mutually cis water ligands.[2]


Iron(III) phosphate is one of the few molluscicides approved for use in the practice of organic farming. Unlike the older metaldehyde, it is non-toxic to pets and wildlife.

It can be used in steel and metal manufacturing processes. When bonded to a metal surface, iron phosphate prevents further oxidation of the metal. Its presence is partially responsible for the corrosion resistance of the Iron pillar of Delhi.

Iron phosphate coatings are also primarily used as base coatings for paint in order to increase adhesion to the iron or steel substrate, and is often used in rustproofing as well. It can also be used for bonding fabrics, wood, and other materials to these surfaces as well. Iron Phosphate coatings are usually applied as part of a painting or powder coating process.


Iron(III) phosphate is not allowed as food additive in European Union. It was withdrawn from the list of allowed substances in the directive 2002/46/EC in 2007.

See also[edit]


  1. ^ Song, Y.; Zavalij, P. Y.; Suzuki, M.; Whittingham, M. S. "New Iron(III) Phosphate Phases: Crystal Structure and Electrochemical and Magnetic Properties" Inorganic Chemistry 2002, vol. 41, 5778-5786. doi:10.1021/ic025688q
  2. ^ Zaghib, K.; Julien, C. M. "Structure and electrochemistry of FePO4·2H2O hydrate" Journal of Power Sources 2005, vol. 142, 279-284.

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