Ammonium dihydrogen phosphate (ADP), also known as monoammonium phosphate (MAP) 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 element ...

with the

chemical formula A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as pare ...

(NH₄)(H₂PO₄). ADP is a major ingredient of agricultural

fertilizers A fertilizer or fertiliser is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrition, plant nutrients. Fertilizers may be distinct from Liming (soil), liming materials or other non- ...

and dry chemical fire extinguishers. It also has significant uses in

optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of optical instruments, instruments that use or Photodetector, detect it. Optics usually describes t ...

and

electronics Electronics is a scientific and engineering discipline that studies and applies the principles of physics to design, create, and operate devices that manipulate electrons and other Electric charge, electrically charged particles. It is a subfield ...

Chemical properties

Monoammonium phosphate is soluble in water and crystallizes from it as the anhydrous

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

in the

tetragonal In crystallography, the tetragonal crystal system is one of the 7 crystal systems. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the Cube (geometry), cube becomes a rectangular Pri ...

system, as elongated prisms or needles. It is practically insoluble in

ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...

.Dejun Xu, Xing Xiong, Lin Yang, Zhiye Zhang, and Xinlong Wang (2016): "Determination of the Solubility of Ammonium Dihydrogen Phosphate in Water-Ethanol System at Different Temperatures from 283.2 to 343.2 K". ''Journal of Chemincal Engineering Data'', volume 61, issue 1, pages 78–82. Solid monoammonium phosphate can be considered stable in practice for temperatures up to 200 °C, when it decomposes into gaseous

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

and molten

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 solution, ...

.G. O. Guerrant and D. E. Brown (196): "Thermal Decomposition of High-Analysis Fertilizers Based on Ammonium Phosphate". ''Journal of Agricultural and Food Chemistry'', volume 13, issue 6, pages 493-497. At 125 °C the

partial pressure In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal g ...

of ammonia is 0.05 mm Hg. A solution of stoichometric monoammonium phosphate is acidic ( pH 4.7 at 0.1% concentration, 4.2 at 5%).Haifa Chemicals Ltd.:
Mono-Ammonium Phosphate 12-61-0
". Product fact sheet, accessed on 2018-08-13.

Preparation

Monoammonium phosphate is industrially prepared by the

exothermic reaction In thermochemistry, an exothermic reaction is a "reaction for which the overall standard enthalpy change Δ''H''⚬ is negative." Exothermic reactions usually release heat. The term is often confused with exergonic reaction, which IUPAC define ...

of phosphoric acid and ammonia in the correct proportions:Martin Bäckman, Martin Gunnarsson, Linnea Kollberg, Martin Müller, and Simon Tallvod (2016):
Production of Monoammonium Phosphate at Yara AB
". Technical Report, Lund University. : + → Crystalline MAP then precipitates.

Uses

Agriculture

The largest use of monoammonium phosphate by weight is in agriculture, as an ingredient of fertilizers. It supplies

soil Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...

with the elements

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

and

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

in a form usable by plants. Its NPK label is 12-61-0 (12-27-0), meaning that it contains 12% by weight of elemental nitrogen and (nominally) 61% of

phosphorus pentoxide Phosphorus pentoxide is a chemical compound with molecular formula Phosphorus, P4Oxygen, O10 (with its common name derived from its empirical formula, P2O5). This white crystalline solid is the anhydride of phosphoric acid. It is a powerful desic ...

, or 27% of elemental phosphorus.

Fire extinguishers

The compound is also a component of the ABC powder in some dry chemical

fire extinguisher A fire extinguisher is a handheld active fire protection device usually filled with a dry or wet chemical used to extinguish or control small fires, often in emergencies. It is not intended for use on an out-of-control fire, such as one which ha ...

Optics

Monoammonium phosphate is a widely used crystal in the field of optics due to its

birefringence Birefringence, also called double refraction, is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are described as birefrin ...

properties. As a result of its tetragonal crystal structure, this material has negative uniaxial optical symmetry with typical refractive indices and at optical wavelengths.

Electronics

Monoammonium phosphate crystals are

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 stress (mechanics), mechanical s ...

, a property required in some active

sonar Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances ( ranging), communicate with or detect objects o ...

transducers A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and contro ...

(the alternative being transducers that use

magnetostriction Magnetostriction is a property of magnetic materials that causes them to change their shape or dimensions during the process of magnetization. The variation of materials' magnetization due to the applied magnetic field changes the magnetostrictive ...

). In the 1950s ADP crystals largely replaced the

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

and Rochelle salt crystals in transducers because they are easier to work than quartz and, unlike Rochelle salt, are not

deliquescent Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption (chemistry), absorption or adsorption from the surrounding Natural environment, environment, which is usually at normal or room temperature. If water mol ...

Toys

Being relatively non-toxic, MAP is also a popular substance for recreational crystal growing, being sold as toy kits mixed with dyes of various colors.

Natural occurrence

The compound appears in nature as the rare mineral biphosphammite. It is formed in

guano Guano (Spanish from ) is the accumulated excrement of seabirds or bats. Guano is a highly effective fertiliser due to the high content of nitrogen, phosphate, and potassium, all key nutrients essential for plant growth. Guano was also, to a le ...

deposits. A related compound, that is the monohydrogen counterpart, is the even more scarce phosphammite.

References

{{Phosphates Phosphates Ammonium compounds Fire suppression agents Inorganic fertilizers