Ferric orthophosphate, Ferric phosphate
3D model (JSmol)
|Density||3.056 g/cm3 (anhydrous)|
2.87 g/cm3 (20 °C, dihydrate)
|Melting point|| 250 °C (482 °F; 523 K) |
0.642 g/100 mL (100 °C)
Heat capacity (C)
|180.5 J/mol·K (dihydrate)|
|171.3 J/mol·K (dihydrate)|
Std enthalpy of
|-1888 kJ/mol (dihydrate)|
|GHS signal word||Warning|
|H315, H319, H335|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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.
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. Iron(III) phosphate is an ideal electrode material for batteries in electric vehicles due to its thermal stability and generally good cyclability.
Iron(III) phosphate is not allowed as food additive in the European Union. It was withdrawn from the list of allowed substances in the directive 2002/46/EC in 2007.
In mammals, Iron phosphate can cause eye, skin, and respiratory tract irritation and may be harmful if swallowed.
Use as an organic pesticide
Pesticide pellets containing iron phosphate plus a chelating agent, such as EDTA, may leach heavy metals from soil into groundwater. A 2006 review of these products by the Research Institute of Organic Agriculture (FiBL), a Swiss organic certification organization, reported the EDTA content and stated products were likely to be no safer than metaldehyde baits. According to a 2012 petition to remove iron(III) phosphate from a list of accepted organic ingredients in the United States, it "appears that all of the ferric phosphate slug and snail baits currently marketed in the U.S. contain EDTA in their formulations".
- Iron(II) phosphate, the lower phosphate of iron
- Lithium iron phosphate battery, a battery that uses iron phosphate
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