Aluminium phosphate

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Not to be confused with Aluminium phosphide.
Aluminium phosphate
Aluminum phosphate
Identifiers
CAS number 7784-30-7 YesY
22784-12-9 (trihydrate)
PubChem 64655
ChemSpider 58204 YesY
UNII F92V3S521O YesY
RTECS number TB6450000
ATC code A02AB03
Jmol-3D images Image 1
Image 2
Properties
Molecular formula AlPO4
Molar mass 121.9529 g/mol
Appearance White, crystalline powder
Density 2.566 g/cm3, solid
Melting point 1,800 °C (3,270 °F; 2,070 K)
Boiling point Decomposes
Solubility in water insoluble
Solubility product, Ksp 6.3×10−19
Solubility Very slightly soluble in HCl and HNO3
Refractive index (nD) 1.546 [1]
Hazards
EU classification Xi
R-phrases R36/37/38
S-phrases S26
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
LD50 4640 mg/kg (rat, oral)
> 4640 mg/kg (rabbit, dermal)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

Aluminium phosphate (AlPO4) is a chemical compound. The anhydrous form is found in nature as the mineral berlinite. Many synthetic forms[2] of anhydrous aluminium phosphate are known. They have framework structures similar to zeolites and some are used as catalysts or molecular sieves. The dihydrate, AlPO4·2H2O is found as the minerals varisciteand meta-variscite.[3] A synthetic hydrated form, AlPO4·1.5H2O is also known.[4] Commercially, an aluminium phosphate gel is available.

Aluminium phosphate (berlinite)[edit]

AlPO4 is isoelectronic with Si2O4, silicon dioxide. Berlinite looks like quartz and has a structure that is similar to quartz with silicon replaced by Al and P. The AlO4 and PO4 tetrahedra alternate. Like quartz, AlPO4 exhibits chirality[5] and piezoelectric properties.[6] Crystalline AlPO4 (berlinite) when heated, converts to tridymite and cristobalite forms, and this mirrors the behaviour of silicon dioxide.[7]

Aluminium phosphate dihydrate (variscite and meta-variscite)[edit]

The structure can be regarded as an assembly of phosphate anions, aluminium cations and water. The aluminium cations are six-coordinate.[3]

Aluminophosphate molecular sieves[edit]

There are many of aluminium phosphate molecular sieves, generically known as "ALPOs". The first ones were reported in 1982.[8] They all share the same chemical composition of AlPO4 and have framework structures with microporous cavities. The frameworks are made up of alternating AlO4 and PO4 tetrahedra. The denser cavity-less crystalline AlPO4 mineral, berlinite, shares the same alternating AlO4 and PO4 tetrahedra.[7] The aluminophosphate framework structures vary one from another in the orientation of the AlO4 tetrahedra and PO4 tetrahedra to form different-sized cavities, and in this respect they are similar to the aluminosilicate zeolites, which differ in having electrically charged frameworks. A typical preparation of an aluminophosphate involves the hydrothermal reaction of phosphoric acid and aluminium in the form of hydroxide, an aluminium salt such as aluminium nitrate salt or alkoxide under controlled pH in the presence of organic amines.[9] These organic molecules act as templates (now termed structure directing agents, SDAs[2]) to direct the growth of the porous framework.[10]

Uses of aluminium phosphate gel[edit]

In medicine an aluminium phosphate sol is used as adsorbent for toxoid and in the dried form, which contains hydrated AlPO4, as an antacid [11] Industrially the Al-PO4-H2O system is used as the basis of many adhesives, binders and cements.[7]

Naturally occurring aluminium phosphate[edit]

Although it is unstable to heat, in geologically stable regions like Australia and Southern Africa, aluminium phosphate is generally the most common form of phosphorus in soils, as it forms when phosphate in rainwater reacts with dissolved aluminium in the soil. Although it is not as insoluble as many other components of soils in those regions, aluminium phosphate can form exceedingly insoluble double salts known as taranakites with many essential elements for plant growth that are normally highly soluble in water, such as potassium and nitrogen.

In coastal areas of South Africa and Namibia, the combination of exceedingly old soils and a high input of phosphate from very fertile oceans due to the Benguela Current causes aluminium phosphate to accumulate to form a concentrated mineral known as aluminium phosphate rock. Only in recent years has there been any interest in the mining of these considerable deposits as a source of phosphorus for agriculture, but there could be considerable economic value if low-cost treatment becomes possible.

References[edit]

  1. ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
  2. ^ a b Chemistry of Zeolites and Related Porous Materials: Synthesis and Structure Ruren Xu, Wenqin Pang, Jihong Yu, Qisheng Huo, Jiesheng Chen, John Wiley & Sons, 2007, ISBN 978-0-470-82233-3
  3. ^ a b Corbridge DEC 2013, Phosphorus: Chemistry, Biochemistry and Technology, 6th ed., CRC Press, Boca Raton, Florida, ISBN 978-1-4398-4088-7
  4. ^ Lagno, Felipe; Demopoulos, George P. (2005). "Synthesis of Hydrated Aluminum Phosphate, AlPO4·1.5H2O (AlPO4−H3), by Controlled Reactive Crystallization in Sulfate Media". Industrial & Engineering Chemistry Research 44 (21): 8033–8038. doi:10.1021/ie0505559. ISSN 0888-5885. 
  5. ^ Tanaka, Yoshikazu; Kojima, Taro; Takata, Yasutaka; Chainani, Ashish; Lovesey, Stephen W.; Knight, Kevin S.; Takeuchi, Tomoyuki; Oura, Masaki; Senba, Yasunori; Ohashi, Haruhiko; Shin, Shik (2010). "Determination of structural chirality of berlinite and quartz using resonant x-ray diffraction with circularly polarized x-rays". Physical Review B 81 (14). doi:10.1103/PhysRevB.81.144104. ISSN 1098-0121. 
  6. ^ Crystal growth of an α-quartz like piezoelectric material, berlinite, Motchany A. I.,Chvanski P. P., Annales de Chimie Science des Materiaux properties, 2001, 26, 199
  7. ^ a b c Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0080379419. 
  8. ^ Wilson, Stephen T.; Lok, Brent M.; Messina, Celeste A.; Cannan, Thomas R.; Flanigen, Edith M. (1982). "Aluminophosphate molecular sieves: a new class of microporous crystalline inorganic solids". Journal of the American Chemical Society 104 (4): 1146–1147. doi:10.1021/ja00368a062. ISSN 0002-7863. 
  9. ^ Zeolites in Industrial Separation and Catalysis Santi Kulprathipanja, John Wiley & Sons, 26 Jan 2010
  10. ^ Zeolites and Catalysis, Jiri Cejka, Avelino Corma, Stacey Zones, John Wiley & Sons, 27 May 2010,ISBN 978-3-527-32514-6
  11. ^ Contemporary Drug Synthesis, Jie Jack Li, Douglas S. Johnson, Drago R. Sliskovic, Bruce D. Roth., John Wiley and Sons, 2004, ISBN 0471-21-480-9

External links[edit]