ZINC PHOSPHIDE

Description

Zinc phosphide, trizinc diphosphide, is an amorphous gray-black powder with a garlic-like odor. It is practically insoluble in water (decomposes slowly), ethanol, slightly soluble in carbon disulfide, and benzene [9, p. 967]. Zinc phosphide is produced by heating finely powdered zinc with phosphorus (10).

Description

Zinc phosphide (Zn3P2) is a synthetic inorganic compound that has widely divergent uses. It was originally prepared in the early 20th century by heating stoichiometric amounts of the elements. Much more recently (2013), Erik J. Luber*, Md Hosnay Mobarok, and Jillian M. Buriak* at Canada’s National Institute for Nanotechnology and the University of Alberta (both in Edmonton) prepared pure nanocrystalline Zn3P2 by treating tri-n-octylphosphine (TOP) with dimethylzinc at 320 °C.
Under ambient conditions, zinc phosphide has a tetragonal crystal structure (shown); it converts to cubic when heated to ≈845 °C. This brings up an unusual situation about Zn3P2’s melting point: Some references report that it melts at 1160 °C or higher, but others give 420 °C. The phase-change temperature clearly indicates that the higher melting point is correct.
The original use for zinc phosphide was as a rodenticide, for burrowing pests such as gophers and moles and for domestic pests such as rats and mice. It is usually combined with baits that the animals ingest. Zn3P2 hydrolyzes slowly in contact with water; but the acidity in the target pest’s stomach rapidly releases highly toxic phosphine gas, a respiratory poison. Phosphine was the Molecule of the Week for October 22, 2018.
The newer use of zinc phosphide is more pleasant and exciting. In 2009, Gregory M. Kimball and co-workers at Caltech (Pasadena, CA) reported that steady-state photoluminescence spectra of Zn3P2 wafers have a fundamental indirect band gap of 1.38 eV, close to the ideal direct band gap value of 1.5 eV. This result indicates that it may be valuable as a semiconductor in photovoltaic cells.
The work of Luber et al., mentioned above, also involved photovoltaics. Their synthetic method produced colloidal semiconducting ≈8-nm nanocrystals with the tetragonal (α-Zn3P2) structure. They found that the optical band gap in this form is 0.5 eV greater than that of bulk Zn3P2. Films prepared via deposition of the nanoparticles were used in heterojunction devices that had excellent rectification behavior. Other data, however, indicated that the particles had phosphorus-rich shells (due to the presence of elemental phosphorus [P(0)]), which hindered performance.
Subsequently, Luber, Buriak, and colleagues developed an alternative method for preparing nanocrystalline zinc phosphide that uses tris(trimethylsilyl)phosphine instead of TOP as the phosphorus source. This change greatly decreased the concentration of P(0) on the particle surfaces.

Chemical properties

Dark gray, gritty powder. Stable if dry. Insoluble in alcohol; soluble in acids; decomposes in water.

Chemical properties

Zinc phosphide is a gray crystalline solid.

The Uses of ZINC PHOSPHIDE

Zinc phosphide has been used since the second world war, and is most commonly used as an effective insecticide and rodenticide. Zinc phosphide is highly toxic due to its production of phosphine gas, and can cause symptoms such as nausea, vomiting and dyspnea in those (animal or human) that are exposed.

General Description

ZINC PHOSPHIDE is a dark gray granular solid. ZINC PHOSPHIDE is slowly decomposed by water giving off phosphine, a flammable poison gas. ZINC PHOSPHIDE is toxic by ingestion. ZINC PHOSPHIDE is used in medicine and as a rat poison.

Reactivity Profile

ZINC PHOSPHIDE is a reducing agent. They slowly generate flammable or noxious gases in contact with water. Phosphides react quickly upon contact with moisture or acids to give the very toxic gas phosphine; phosphides also can react vigorously with oxidizing materials. In general, materials in this group are incompatible with oxidizers such as atmospheric oxygen. They are violently incompatible with acids, particularly oxidizing acids.

Health Hazard

ZINC PHOSPHIDE is very caustic when ingested. ZINC PHOSPHIDE reacts with water and acid in the stomach and causes severe irritation. The probable oral lethal dose is 5-50 mg/kg, or between 7 drops and 1 teaspoonful for a 70 kg (150 lb.) person. Most patients die after about 30 hours from peripheral vascular collapse secondary to the compound's direct effects. Extensive liver damage and kidney damage can also occur. Ingestion of 4-5 grams has produced death in human adults, but also doses of 25 to 50 grams have been survived. The lowest oral lethal dose reported for women is 80 mg/kg.

Fire Hazard

When heated to decomposition, ZINC PHOSPHIDE emits toxic fumes of phosphorus and zinc oxides. Irritating oxides of phosphorus may be formed in fires. May ignite in presence of moisture. Contact with water produces flammable gas. Runoff to sewer may create fire or explosion hazard. Decomposed slowly by water giving off phosphine, a flammable poison gas. Reacts violently with concentrated sulfuric acid, nitric acid, and other oxidizing agents. Reacts with hydrochloric acid or sulfuric acid with the evolution of spontaneously flammable phosphine. May ignite in the presence of moisture, or evolve flammable gas. Stable unless exposed to moisture; toxic phosphine gas may then be released and collected in closed spaces. Hazardous polymerization may not occur.

Agricultural Uses

Rodenticide: A U.S. EPA restricted Use Pesticide (RUP). Registered for use in EU countries . Zinc phosphide reacts with the acidic conditions in the gut to form phosphine gas, which interferes with cell respiration. The rodenticide may be used to control many species of rodents, including mice, ground squirrels, prairie dogs, voles, moles, rats, muskrats, nutria and gophers. It may be used as an indoor or outdoor spot treatment for rodents as well as around burrows or underground in orchards, vineyards, various food crops, range lands, and non-crop areas. Zinc phosphide is formulated as a bait/solid, dust, granular, pellet/ tablet or wettable powder and is also applied as a broadcast treatment by ground or aerial applications.

Trade name

BAKER BRAND®[C]; BLUE-OX®; E-Z FLO®[C]; GOPHA-RID®; HOPKINS®; KILRAT®; MOLETOX II®; MOUS-CON®; MR. KILL RAT®; MR RAT GUARD®; NOTT ZINC PHOSPHIDE 93®; RATOL®; ROBAN II AG®[C]; RUMETAN®; ZINC- TOX®; ZP®

Safety Profile

Human poison by ingestion causing nausea, vomiting, death. Flammable when exposed to heat or flame. This material is stable while kept dry. In moist air, it decomposes slowly. Reacts violently with acids or acid fumes to emit the hghly toxic and flammable phosphine. Violent reaction with concentrated sulfuric acid, nitric acid, and oxidzing materials. Incompatible with HCl, H2SO4. When heated to decomposition it emits toxic fumes of POx and ZnO. Used as an acute rodenticide. See also PHOSPHIDES and ZINC COMPOUNDS.

Potential Exposure

It is used as an acute single feeding rodenticide.

Shipping

UN1714 Zinc phosphide, Hazard Class: 4.3; Labels: 4.3-Dangerous when wet material, 6.1-Poisono us materials.

Incompatibilities

Dust may form explosive mixture with air. Heat and contact with water causes decomposition, producing toxic and flammable fumes of phosphorus, zinc oxides; and toxic and flammable phosphine gas. Reacts violently with strong acids, including nitric, hydrochloric acid or sulfuric acid with the evolution of spontaneously flammable phosphine gas. Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact can cause fires or explosions. Keep away from alkaline materials, strong bases. carbon dioxide, halogenated agents.

Waste Disposal

Consult with environmental regulatory agencies for guidance on acceptable disposal practices. Generators of waste containing this contaminant (≥100 kg/mo) must conform to EPA regulations governing storage, transportation, treatment, and waste disposal. Vanadium pentoxide may be salvaged or disposed of in a sanitary landfill.