Ferric phosphate

Iron(III) phosphate

Names
IUPAC name Iron(III) phosphate
Other names Ferric orthophosphate, Ferric phosphate
Identifiers
CAS Number	10045-86-0 (anhydrous) 13463-10-0 (dihydrate)
3D model (Jmol)	Interactive image
ChEBI	CHEBI:131371 Y
ChemSpider	23244 Y
ECHA InfoCard	100.030.123
PubChem CID	24861
UNII	N6BAA189V1 Y
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	FePO4
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)
Magnetic susceptibility (χ)	+11,500.0·10−6 cm3/mol
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)
Hazards
GHS pictograms
GHS signal word	Warning
GHS hazard statements	H315, H319, H335
GHS precautionary statements	P261, P305+351+338
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, also ferric 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.

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.

Iron(III) phosphate is one of the few molluscicides approved for use in the practice of organic farming, but unlabelled addition of EDTA contradicts such labelling.

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.