Aluminium phosphate is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one ele ...

. In nature it occurs as the mineral berlinite. Many synthetic forms of aluminium phosphate are known. They have framework structures similar to

zeolites Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ･y where is either a metal ion or H+. These ...

and some are used as

catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

s, ion-exchangers or

molecular sieves A molecular sieve is a material with pores (very small holes) of uniform size. These pore diameters are similar in size to small molecules, and thus large molecules cannot enter or be adsorbed, while smaller molecules can. As a mixture of molecu ...

. Commercial aluminium phosphate gel is available.

Berlinite

AlPO₄ is

isoelectronic Isoelectronicity is a phenomenon observed when two or more molecules have the same structure (positions and connectivities among atoms) and the same electronic configurations, but differ by what specific elements are at certain locations in th ...

with Si₂O₄,

silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

. 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 Chirality is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is distinguishable from i ...

and

piezoelectric Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress. The word ' ...

properties. When heated, crystalline AlPO₄ (berlinite) converts to

tridymite Tridymite is a high-temperature polymorph of silica and usually occurs as minute tabular white or colorless pseudo-hexagonal crystals, or scales, in cavities in felsic volcanic rocks. Its chemical formula is Si O2. Tridymite was first described ...

and

cristobalite Cristobalite is a mineral polymorph of silica that is formed at very high temperatures. It has the same chemical formula as quartz, SiO2, but a distinct crystal structure. Both quartz and cristobalite are polymorphs with all the members of the q ...

forms, and this mirrors the behaviour of

Uses

Molecular sieves

There are many types of aluminium phosphate

molecular sieve A molecular sieve is a material with pores (very small holes) of uniform size. These pore diameters are similar in size to small molecules, and thus large molecules cannot enter or be adsorbed, while smaller molecules can. As a mixture of molec ...

s, 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 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 Aluminosilicate minerals ( IMA symbol: Als) are minerals composed of aluminium, silicon, and oxygen, plus countercations. They are a major component of kaolin and other clay minerals. Andalusite, kyanite, and sillimanite are naturally ...

zeolite Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ･y where is either a metal ion or H+. These ...

s, which differ in having electrically charged frameworks. A typical preparation of an aluminophosphate involves the

hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

reaction of

phosphoric acid Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solutio ...

and aluminium in the form of

hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water ...

, an aluminium salt such as aluminium nitrate salt or alkoxide under controlled pH in the presence of organic

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent su ...

s. These organic molecules act as templates (now termed structure directing agents, SDAs) to direct the growth of the porous framework.

Other

Along with

aluminium hydroxide Aluminium hydroxide, Al(OH)3, is found in nature as the mineral gibbsite (also known as hydrargillite) and its three much rarer Polymorphism (materials science), polymorphs: bayerite, doyleite, and nordstrandite. Aluminium hydroxide is Amphoter ...

, aluminium phosphate is one of the most common

immunologic adjuvant In immunology, an adjuvant is a substance that increases or modulates the immune response to a vaccine. The word "adjuvant" comes from the Latin word ''adiuvare'', meaning to help or aid. "An immunologic adjuvant is defined as any substance that ...

s (efficiency enhancers) in

vaccination Vaccination is the administration of a vaccine to help the immune system develop immunity from a disease. Vaccines contain a microorganism or virus in a weakened, live or killed state, or proteins or toxins from the organism. In stimulating ...

s. Aluminium adjuvant use is widespread due to their cheap price, long history of use, safety and efficiency with most

antigen In immunology, an antigen (Ag) is a molecule or molecular structure or any foreign particulate matter or a pollen grain that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response. ...

s. It's unknown how such salts function as adjuvants. Similar to aluminum hydroxide, AlPO₄ is used as an

antacid An antacid is a substance which neutralizes stomach acidity and is used to relieve heartburn, indigestion or an upset stomach. Some antacids have been used in the treatment of constipation and diarrhea. Marketed antacids contain salts of alumi ...

. It neutralizes stomach acid ( HCl) by forming AlCl₃ with it. Up to 20% of aluminum from ingested antacid salts can be absorbed from the gastrointestinal tract – despite some unverified concerns about the neurological effects of aluminum, aluminum phosphate and hydroxide salts are thought to be safe as antacids in normal use, even during pregnancy and breastfeeding. Additional uses for AlPO₄ in combination with or without other compounds are white colorants for pigments, corrosion inhibitors, cements and

dental cement Dental cements have a wide range of dental and orthodontic applications. Common uses include temporary restoration of teeth, cavity linings to provide pulpal protection, sedation or insulation and cementing fixed prosthodontic appliances. Recent u ...

s. Related compounds have also similar uses. For example, Al(H₂PO₄)₃ is used in dental cements, metal coatings, glaze compositions and

refractory In materials science, a refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycrystalline, polyphase ...

binders; and Al(H₂PO₄)(HPO₄) is used cement and refractory binders and adhesives.

Related compounds

AlPO₄·2H₂O dihydrate is found as the minerals variscite and meta-variscite. Aluminium phosphate dihydrate (variscite and meta-variscite) has a structure that can be regarded as an assembly of

tetra Terrestrial Trunked Radio (TETRA; formerly known as Trans-European Trunked Radio), a European standard for a trunked radio system, is a professional mobile radio and two-way transceiver specification. TETRA was specifically designed for use by ...

- and

octahedral In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at ea ...

units of phosphate anions, aluminium cations and water. Al³⁺ ions are 6-coordinate and PO₄^3- ions are 4-coordinate.Corbridge, p. 207-208 A synthetic hydrated form, AlPO₄·1.5H₂O is also known.

References

Citations

External links

MSDS PDF
{{Antacids Phosphates Aluminium compounds Dehydrating agents Antacids