The aluminum phosphate is an inorganic solid formed by an aluminum ion Al3+ and a phosphate ion PO43-. Its chemical formula is AlPO4. It is a white solid whose crystalline structure is similar to that of silica SiOtwo. It is insoluble in water.
It can be obtained from alumina (AltwoOR3) and phosphoric acid (H3PO4). It can also be obtained starting from aqueous solutions of aluminum chloride (AlCl3) and sodium phosphate (Na3PO4).
Aluminum phosphate has a very high melting point, which is why it is widely used as a component of refractory ceramics, that is, ceramics that withstand very high temperatures..
It is also used as an antacid for the stomach, in mixtures for the repair of teeth and as an adjuvant to vaccines, that is, to stimulate the body's immune response.
Some refractory concretes have AlPO4 in its composition, which increases the mechanical and high-temperature support properties of this type of cement.
It has been used as a protective shield to prevent combustible materials such as certain polymers from burning.
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The AlPO4 It is formed by an aluminum cation Al3+ and a phosphate anion PO43-.
Crystalline aluminum phosphate is also called berlinite or alpha phase (α-AlPO4) and its crystals are similar to quartz.
The alpha phase of aluminum phosphate is a solid formed by a covalent network of PO tetrahedra4 and AlPO4 that alternate and are linked by oxygen atoms.
This structure is isomorphic with silica, that is, it has the same shape as that of silica SiOtwo.
- Aluminum phosphate
- Aluminum monophosphate
- Aluminum salt of phosphoric acid.
Solid white crystalline.
121.93 g / mol
1800 ºC
2.56 g / cm3
Insoluble in water
The structure of the AlPO4 is very similar to silica SiOtwo, so it shares many physical and chemical properties of this.
Aluminum phosphate is a highly refractory material, that is, it resists very high temperatures without changing its physical state or structure and without decomposing.
The AlPO4 crystalline or berlinite when heated it converts to a tridymite type structure and then cristobalite type, other forms of this compound that resemble silica SiOtwo.
Aluminum Phosphate AlPO4 can be obtained by the reaction between phosphoric acid H3PO4 and alumina AltwoOR3. Temperature application required, for example between 100 and 150 ° C.
To thetwoOR3 + 2 h3PO4 = 2 AlPO4 + 3 HtwoOR
It can also be obtained by joining an aqueous solution of aluminum chloride AlCl3 with an aqueous solution of sodium phosphate Na3PO4:
AlCl3 + Na3PO4 = AlPO4 + 3 NaCl
Aluminum Phosphate AlPO4 is often found in the constitution of alumina ceramics.
Ceramic with high alumina content is one of the materials that, due to its hardness, is used in applications where it is required to resist high loads and severe conditions..
This type of ceramic is resistant to corrosion, to high temperature environments, to the presence of hot steam or to reducing atmospheres such as carbon monoxide (CO)..
Alumina ceramic also has low electrical and thermal conductivity, which is why it is used to make refractory bricks and electrically insulating components..
Because aluminum phosphate forms at a much lower temperature than silica SiOtwo, its production is cheaper, which constitutes an advantage in the manufacture of ceramics suitable for demanding services.
Al alumina is usedtwoOR3 and phosphoric acid H3PO4 in aqueous medium.
The preferred formation pH is 2-8, as there is an abundance of dissolved phosphoric acid species, such as HtwoPO4- and HPO4two-. At acid pH the concentration of Al ions3+ is high, coming from the dissolution of alumina AltwoOR3.
First, a hydrated aluminum diphosphate trihydrogen gel AlH is formed.3(PO4)two.HtwoOR:
To the3+ + HtwoPO4- + HPO4two- + HtwoO ⇔ AlH3(PO4)3.HtwoOR
However, there comes a time when the pH of the solution drops and becomes neutral, where the alumina AltwoOR3 it has a low solubility. At this time, the insoluble alumina forms a layer on the surface of the particles, preventing the reaction from continuing..
Therefore it is necessary to increase the solubility of the alumina and this is achieved by gently heating. On heating to 150 ° C the gel continues the reaction with alumina AltwoOR3 releasing water and crystalline berlinite (alpha-AlPO4).
To thetwoOR3 + 2 AlH3(PO4)3.HtwoO → AlPO4 + 4 htwoOR
The berlinite binds the individual particles and forms the ceramic.
The AlPO4 It is used as an antacid, as an adsorbent, as a molecular sieve, as a catalyst support and as a coating to improve resistance to hot corrosion. Below other applications.
Aluminum phosphate is an ingredient in refractory concretes or heat resistant concretes.
Provides excellent mechanical and refractive properties to these concretes, such as heat resistance. In the temperature range between 1400-1600 ° C, cellular concrete based on aluminum phosphate is one of the most efficient materials as a thermal insulator..
It does not require drying, its hardening is achieved through a self-propagating exothermic reaction. It is possible to prepare bricks of this material of any shape and size.
Aluminum phosphate is part of dental cements or materials used to heal decayed teeth.
In dental cements, alumina is used as a moderator of acid-base reactions, where the moderating effect is due to the formation of aluminum phosphate on the particles of other materials..
These cements have a very high resistance to compression and tension, which is due to the presence of aluminum phosphate.
The AlPO4 it has been used for many years in various human vaccines to enhance the body's immune response. It is said that the AlPO4 it is an "adjuvant" to vaccines. The mechanism is still not well understood.
It is known that the immunostimulating effect of AlPO4 it depends on the process of adsorption of the antigen to the adjuvant, that is, on the way in which it adheres to it. An antigen is a compound that upon entering the body generates the formation of antibodies to fight a specific disease.
Antigens can be adsorbed to AlPO4 by electrostatic interactions or by binding with ligands. They are adsorbed on the surface of the adjuvant.
It is further believed that the particle size of AlPO4 it also has influence. The smaller the particle size the antibody response is greater and longer lasting..
The AlPO4 It has been used as a fire retardant and to prevent the combustion or burning of certain polymers.
The addition of AlPO4 to a polypropylene polymer that already has a flame retardant causes a synergistic effect between both retarders, which means that the effect is much greater than that of both fire retardants separately.
When the polymer is subjected to combustion or burned in the presence of AlPO4, an aluminum metaphosphate is formed that penetrates the charred surface and fills the pores and cracks of this.
This leads to the formation of a highly efficient protective shield to prevent burning or combustion of the polymer. In other words the AlPO4 seals charred surface and prevents polymer from burning.
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