Phosphoric acid, aluminium salt (1:1)
3D model (JSmol)
|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)|
Solubility product (Ksp)
|Solubility||Very slightly soluble in HCl and HNO3|
Refractive index (nD)
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
|4640 mg/kg (rat, oral)
> 4640 mg/kg (rabbit, dermal)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Aluminium phosphate (AlPO4) is a chemical compound. The anhydrous form is found in nature as the mineral berlinite. Many synthetic forms 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 variscite and meta-variscite. A synthetic hydrated form, AlPO4·1.5H2O is also known. Commercially, an aluminium phosphate gel is available.
Aluminium phosphate (berlinite)
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 and piezoelectric properties. Crystalline AlPO4 (berlinite) when heated, converts to tridymite and cristobalite forms, and this mirrors the behaviour of silicon dioxide.
Aluminophosphate molecular sieves
There are many of aluminium phosphate molecular sieves, generically known as "ALPOs". The first ones were reported in 1982. 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. 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. These organic molecules act as templates (now termed structure directing agents, SDAs) to direct the growth of the porous framework.
Aluminium phosphate dihydrate (variscite and meta-variscite) has a structure that can be regarded as an assembly of phosphate anions, aluminium cations and water. The aluminium cations are six-coordinate.
In medicine an aluminium phosphate sol or gel is used as adsorbent for toxoid and in the dried form, which contains hydrated AlPO4, as an antacid. Industrially the Al-PO4-H2O system is used as the basis of many adhesives, binders and cements.
Aluminium dihydrogenphosphate (Al(H2PO4)3) is a related material formed from combining phosphate and aluminium salts at low pH.
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