Iron(III) 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)
ChEBI	CHEBI:131371
ChemSpider	23244
Jmol interactive 3D	Image
PubChem	24861
InChI InChI=1S/Fe.H3O4P/c;1-5(2,3)4/h;(H3,1,2,3,4)/q+3;/p-3 Key: WBJZTOZJJYAKHQ-UHFFFAOYSA-K
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/cm^3 (anhydrous) 2.87 g/cm^3 (20 °C, dihydrate)
Melting point	250 °C (482 °F; 523 K) (dihydrate) decomposes[1]
Solubility in water	anhydrous: insoluble dihydrate: 0.642 g/100 mL (100 °C)[1]
Thermochemistry
Specific heat capacity (C)	180.5 J/mol·K (dihydrate)[1]
Std molar entropy (S^o298)	171.3 J/mol·K (dihydrate)[1]
Std enthalpy of formation (ΔfH^o298)	-1888 kJ/mol (dihydrate)[1]
Hazards
GHS pictograms	[2]
GHS signal word	Warning
GHS hazard statements	H315, H319, H335[2]
GHS precautionary statements	P261, P305+351+338[2]
EU classification (DSD)	Xi
R-phrases	R36/37/38
S-phrases	S26, S36
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,^[3][4] 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.^[5][6]

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.^[7]

Uses

Iron(III) phosphate is one of the few molluscicides approved for use in the practice of organic farming, but unlabeled addition of EDTA contradicts such labeling.^[8]

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

In mammals, Iron phosphate can cause eye, skin, and respiratory tract irritation and may be harmful if swallowed.

Controversial Use as Organic Pesticide

Iron phosphate containing slug baits are fairly new in the garden and their danger is not yet fully researched or understood. ^[9]

In the United States, unlisted addition of EDTA (ethylene-diamine-tetraacetic acid) to Iron phosphate containing products (such as Sluggo) greatly increases the toxicity.^[10]

Pellets containing iron phosphate plus chelating agents are consumed by earthworms and other invertebrates.^[11] The iron EDTA complex formed by the reaction of ferric EDTA with hydroxide ions, and the potential for EDTA to leach heavy metals from soil into groundwater, makes its use in organic gardening questionable.^[12]

A 2006 review of these products by the Swiss organic certification organization (FiBL) discovered the EDTA content and stated products were likely no safer than the metaldehyde baits.^[13] According to a 2012 petition to remove ferric phosphate (III) from a list of accepted organic ingredients, it "appears that all of the ferric phosphate slug and snail baits currently marketed in the U.S. contain EDTA in their formulations.^[14]

See also

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

References

1. "iron(III) phosphate dihydrate". chemister.ru. Retrieved 3 July 2014.
2. Sigma-Aldrich Co., Iron(III) phosphate dihydrate. Retrieved on 2014-05-03.
3. "Iron(III) Phosphate". NIH, U.S. National Library of Medicine. Retrieved 22 January 2016.
4. "FERRIC PHOSPHATE". EndMemo.com. Retrieved 22 January 2016.
5. Roncal-Herrero, T., Rodriguez-Blanco, J.D., Benning, L.G., Oelkers, E.H. (2009) Precipitation of Iron and Aluminum Phosphates Directly from Aqueous Solution as a Function of Temperature from 50 to 200°C. Crystal Growth & Design, 9, 5197-5205. doi: 10.1021/cg900654m.
6. Song, Y.; Zavalij, P. Y.; Suzuki, M.; Whittingham, M. S. (2002). "New Iron(III) Phosphate Phases: Crystal Structure and Electrochemical and Magnetic Properties" (PDF). Inorganic Chemistry 41 (22): 5778–5786. doi:10.1021/ic025688q. PMID 12401083. Retrieved 3 July 2014.
7. Zaghib, K.; Julien, C. M. (2005-01). "Structure and electrochemistry of FePO₄·2H₂O hydrate". Journal of Power Sources 142: 279–284. doi:10.1016/j.jpowsour.2004.09.042. Retrieved 3 July 2014. Check date values in: |date= (help)
8. "COMMISSION REGULATION (EC) No 889/2008". European Union law. Retrieved 3 July 2014.
9. http://blog.oregonlive.com/pethealth/2008/07/gardners_beware_of_socalled_pe.html
10. http://www.hostalibrary.org/firstlook/RRIronPhosphate.htm
11. http://www.biosci.ohio-state.edu/~soilecol/Full%20articles/2008/Crop%20Protection%2028.pdf
12. http://www.regional.org.au/au/asa/2001/6/c/young.htm
13. http://www2.eduskunta.fi/kerhot/luonto/eurosiili/pdf/FIBL_FeP_Jan06_E.pdf
14. https://www.ams.usda.gov/sites/default/files/media/Ferric%20Phosphate%20to%20be%20removed%20Proposal.pdf

External links