ALUMINUM PHOSPHIDE (AIP): STRUCTURE, PROPERTIES, USES, RISKS - CHEMISTRY - 2025

The aluminum phosphide is an inorganic compound consisting of an aluminum atom (A's) and a phosphorus atom (P). Its chemical formula is AlP. It is a solid dark gray or, if very pure, yellow. It is an extremely toxic compound for living beings.

Aluminum phosphide reacts with moisture to form phosphine or phosphane PH ₃, which is a poisonous gas. For this reason, AlP must not come into contact with water. Reacts strongly with acids and alkaline solutions.

Aluminum phosphide. همان. Source: Wikimedia Commons.

It was used in the past to eliminate pests such as insects and rodents in places where cereal grains and other agricultural products were stored. However, due to its high danger it has been banned in most countries of the world.

Currently, its usefulness in the electronics area is being theoretically investigated using computers that calculate the possibility of obtaining semiconductor AlP nanotubes, that is, extremely small tubes that can transmit electricity only under certain conditions.

Aluminum phosphide is a very dangerous compound, it must be handled with safety equipment such as gloves, glasses, respirators and protective clothing.

Structure

The aluminum phosphide AlP is formed by the union of an aluminum atom Al and a phosphorus atom P. The bond between both is covalent and triple, therefore it is very strong.

Aluminum in AlP has an oxidation state of +3 and phosphorus has a valence of -3.

Structure of aluminum phosphide where the triple bond between aluminum (Al) and phosphorus (P) atoms can be observed. Claudio Pistilli. Source: Wikimedia Commons.

Nomenclature

- Aluminum phosphide

Properties

Physical state

Dark gray or dark yellow or green crystalline solid. Cubic crystals.

Molecular weight

57.9553 g / mol

Melting point

2550 ºC

Density

2.40 g / cm ³ at 25 ° C

Solubility

It decomposes in water.

Chemical properties

Reacts with moisture to give phosphine or phosphane PH ₃ which is a flammable and poisonous compound. Phosphine or phosphane spontaneously ignites on contact with air, except if excess water is present.

The reaction of aluminum phosphide with water is as follows:

Aluminum Phosphide + Water → Aluminum Hydroxide + Phosphine

AlP + 3 H ₂ O → Al (OH) ₃ + PH ₃ ↑

The commercial presentations have aluminum carbonate Al ₂ (CO ₃) ₃ to prevent the autoignition of phosphine that occurs when AlP comes into contact with moisture in the air.

AlP is stable when dry. Reacts violently with acids and alkaline solutions.

Aluminum Phosphide AlP does not melt, sublime, or thermally decompose at temperatures as high as 1000 ° C. Even at this temperature its vapor pressure is very low, that is, it does not evaporate at that temperature.

When heated to decomposition it emits toxic phosphorus oxides. In contact with metals, it can emit flammable hydrogen gases H ₂.

Other properties

When it is pure it shows a yellowish coloration, when it is mixed with residues of the preparation reaction it presents a color from gray to black.

Its low volatility excludes that it has any odor, so the garlic smell that it sometimes emits is due to the phosphine PH ₃ that is formed in the presence of humidity.

Obtaining

Aluminum phosphide can be obtained by heating a mixture of powdered aluminum metal (Al) and red phosphor element (P).

Due to the affinity of phosphorus (P) for oxygen (O ₂) and that of aluminum (Al) for oxygen and nitrogen (N ₂), the reaction must be carried out in an atmosphere free of these gases, such as an atmosphere hydrogen (H ₂) or natural gas.

The reaction is started by rapidly heating a zone of the mixture until the reaction starts, which is exothermic (heat is produced during the reaction). From that moment the reaction proceeds rapidly.

Aluminum + Phosphorus → Aluminum Phosphide

4 Al + P ₄ → 4 AlP

Applications

In pest elimination (discontinued use)

Aluminum phosphide was used in the past as an insecticide and as a rodent killer. However, although it has been banned for its toxicity, it is still used in some parts of the world.

It is used for fumigation in confined spaces where processed or unprocessed agricultural food products (such as cereals), animal feed and non-food products are found.

The goal is to control insects and rodents that attack stored items, whether they are edible or not.

It allows to control rodents and insects in non-domestic, agricultural or non-agricultural areas, spraying outdoors or in their burrows and nests to prevent them from transmitting certain diseases.

Rats and mice are pests that attack cereal storage places. Some years ago they were fought with aluminum phosphide. Author: Andreas N. Source: Pixabay.

The rodents were controlled by placing aluminum phosphide in their burrows. Author: Foto-Rabe. Source: Pixabay.

Its form of use consists of exposing AlP to air or humidity, since phosphine or phosphane PH _{3 is released,} which generates damage to many organs of the pest to be eliminated.

The insects were also killed with AlP aluminum phosphide. Author: Michael Podger. Source: Unsplash.

In other applications

Aluminum phosphide AlP is used as a source of phosphine or phosphane PH ₃ and is being used in semiconductor research.

Phosphane or phosphine PH ₃, a compound that is formed when aluminum phosphide AlP comes into contact with water. NEUROtiker. Source: Wikimedia Commons.

Theoretical investigation of AlP nanotubes

Theoretical studies have been carried out on the formation of aluminum phosphide AlP nanotubes. Nanotubes are very small and very thin cylinders that can be visible only with an electron microscope.

AlP nanotubes with boron

Theoretical studies carried out through computational calculations show that the impurities that could be added to the AlP nanotubes could change the theoretical properties of these.

For example, it is estimated that adding boron (B) atoms to AlP nanotubes could turn them into p-type semiconductors. A semiconductor is a material that behaves as a conductor of electricity or as an insulator depending on the electric field to which it is subjected.

And a p-type semiconductor is when impurities are added to the material, in this case AlP is the starting material and boron atoms would be the impurities. Semiconductors are useful for electronics applications.

AlP nanotubes with altered structure

Some scientists have performed calculations to determine the effect of changing the crystal lattice structure of AlP nanotubes from hexagonal to octahedral.

They found that manipulation of the crystal lattice structure could be used to adjust the conductivity and reactivity of AlP nanotubes and design them to be useful for electronics and optics applications.

Risks

Contact with Aluminum Phosphide can irritate the skin, eyes, and mucous membranes. If swallowed or inhaled it is toxic. Can be absorbed through the skin with toxic effects.

If AlP comes into contact with water it reacts and forms phosphine or phosphane PH ₃ which is extremely flammable as it ignites in contact with air. Hence it can explode. Furthermore, phosphine causes the death of humans and animals.

As aluminum phosphide is an inexpensive pesticide, its use is a common cause of poisoning in people and carries a high mortality rate.

Aluminum Phosphide is extremely dangerous. Author: OpenClipart-Vectors. Source: Pixabay.

It reacts with the humidity of the mucous membranes and with the hydrochloric acid HCl in the stomach, forming the very toxic phosphane gas PH ₃. Therefore, by inhalation and by ingestion, phosphine is formed within the body, with fatal effects.

Its ingestion causes gastrointestinal tract bleeding, cardiovascular collapse, neuropsychiatric disorders, respiratory and renal failure within a few hours.

AlP is very toxic to all terrestrial and aquatic animals.

References

1. US National Library of Medicine. (2019). Aluminum phosphide. Recovered from pubchem.ncbi.nlm.nih.gov.
2. Sjögren, B. et al. (2007). Aluminum. Other aluminum compounds. In Handbook on the Toxicology of Metals (Third Edition). Recovered from sciencedirect.com.
3. Gupta, RC and Crissman, JW (2013). Safety Assessment including Current and Emerging Issues in Toxicology Pathology. Human Risk. In Haschek and Rousseaux's Handbook of Toxicology Pathology (Third Edition). Recovered from sciencedirect.com.
4. White, WE and Bushey, AH (1944). Aluminum Phosphide - Preparation and Composition. Journal of The American Chemical Society 1944, 66, 10, 1666-1672. Recovered from pubs.acs.org.
5. Mirzaei, Maryam and Mirzaei, Mahmoud. (2011). A theoretical study of boron-doped aluminum phosphide nanotubes. Computational and Theoretical Chemistry 963 (2011) 294-297. Recovered from sciencedirect.com.
6. Takahashi, L. and Takahashi, K. (2018). Tuning the Electronic Structure of an Aluminum Phosphide Nanotube through Configuration of the Lattice Geometry. ACS Appl. Nano Mater. 2018, 1, 501-504. Recovered from pubs.acs.org.
7. Gupta, PK (2016). Toxic effects of pesticides (agrochemicals). Aluminum Phosphide. In Fundamentals of Toxicology. Recovered from sciencedirect.com.