|Jmol-3D images||Image 1|
|Molar mass||258.12 g/mol|
|Appearance||gray tetragonal crystals|
|Melting point||1,160 °C (2,120 °F; 1,430 K)|
|Solubility in water||insoluble|
|Solubility||insoluble in ethanol, soluble in benzene, reacts with acids|
|Crystal structure||Tetragonal, tP40|
|Space group||P42/nmc, No. 137|
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
Zinc phosphide (Zn3P2) is the inorganic chemical compound. It is a grey solid, although commercial samples are often dark or even black. It is used as a rodenticide. Zn3P2 is a semiconductor with a direct band gap of 1.5 eV. and may have applications in photovoltaic cells. A second zinc phosphide is known, with the stoichiometry ZnP2.
Synthesis and reactions
Zinc phosphide can be prepared by the reaction of zinc with phosphorus; however, for critical applications, additional processing to remove arsenic compounds may be needed.
- 3 Zn + 2 P → Zn3P2
- Zn3P2 + 6 H2O → 2 PH3 + 3 Zn(OH)2
Zn3P2 has two forms, a room temperature tetragonal form which converts to a cubic form at around 845 °C.  In the room temperature form there are discrete P atoms, zinc atoms are terahedrally coordinated and phosphorus six coordinate, with zinc atoms at 6 of the vertices of a distorted cube. ZnP2 has two forms a lower temperature red tetragonal form and a black monoclinic form. In both of these there are chains of P atoms, helical in the tetragonal, semi-spiral in the monoclinic.
Metal phosphides have been used as rodenticides. A mixture of food and zinc phosphide is left where the rodents can eat it. The acid in the digestive system of the rodent reacts with the phosphide to generate the toxic phosphine gas. This method of vermin control has possible use in places where rodents immune to other common poisons. Other pesticides similar to zinc phosphide are aluminium phosphide and calcium phosphide.
Zinc phosphide is typically added to rodent baits in amount of around 0.75-2%. Such baits have strong, pungent garlic-like odor characteristic for phosphine liberated by hydrolysis. The odor attracts rodents, but has a repulsive effect on other animals; birds, notably wild turkeys, are not sensitive to the smell. The baits have to contain sufficient amount of zinc phosphide in sufficiently attractive food in order to kill rodents in a single serving; a sublethal dose may cause aversion towards zinc-phosphide baits encountered by surviving rodents in the future.
Rodenticide-grade zinc phosphide usually comes as a black powder containing 75% of zinc phosphide and 25% of antimony potassium tartrate, an emetic to cause vomiting if the material is accidentally ingested by humans or domestic animals. However, it is still effective against rats, mice, guinea pigs and rabbits, none of which have a vomiting reflex.
Zinc phosphide use in New Zealand
The New Zealand Environmental Protection Authority has approved the import and manufacture of Microencapsulated Zinc Phosphide (MZP Paste) for the ground control of possums. The application was made by Pest Tech Limited, with support from Connovation Ltd, Lincoln University and the Animal Health Board. It will be used as an additional vertebrate poison in certain situations. Unlike 1080 poison, it cannot be used for aerial application.
Zinc phosphide is highly toxic.
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