Iron(III) phosphate

Iron(III) phosphate

Iron(III) phosphate pentahydrate
Names
IUPAC name Iron(III) phosphate
Other names Ferric orthophosphate, Ferric phosphate
Identifiers
CAS Number	10045-86-0 (anhydrous) 13463-10-0 (dihydrate)
ChemSpider	23244 Y
Jmol 3D model	Interactive image
PubChem	24861
InChI InChI=1S/Fe.H3O4P/c;1-5(2,3)4/h;(H3,1,2,3,4)/q+3;/p-3 Y Key: WBJZTOZJJYAKHQ-UHFFFAOYSA-K Y
SMILES [O-]P(=O)([O-])[O-].[Fe+3]
Properties
Chemical formula	FeO4P
Molar mass	150.81 g·mol−1
Appearance	yellow-brown solid
Density	3.056 g/cm3 (anhydrous) 2.87 g/cm3 (20 °C, dihydrate)
Melting point	250 °C (482 °F; 523 K) (dihydrate) decomposes
Solubility in water	anhydrous: insoluble dihydrate: 0.642 g/100 mL (100 °C)
Thermochemistry
Specific heat capacity (C)	180.5 J/mol·K (dihydrate)
Std molar entropy (So298)	171.3 J/mol·K (dihydrate)
Std enthalpy of formation (ΔfHo298)	-1888 kJ/mol (dihydrate)
Vapor pressure	{{{value}}}
Except where otherwise noted, 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.

Structure

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.

Uses

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 phosphate can also be used as an intercalation electrode in a lithium-ion battery despite having low electronic conductivity. However, in recent years its use as an electrode material has been increasingly more common as materials engineers have overcome the electronic conductivity issue. FePO4 is an ideal electrode material for batteries in electric vehicles due to its thermal stability and generally good cyclability.

Legislation

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.

Safety

Can cause eye, skin, and respiratory tract irritation. May be harmful if swallowed. Avoid inhalation of dusts.

See also

• Iron(II) phosphate, the lower phosphate of iron
• Lithium iron phosphate battery, a battery that uses iron phosphate