Calcium phosphide

Calcium phosphide (CP, Ca₃P₂) is a chemical that has uses in incendiary bombs. It has the appearance of red-brown crystalline powder or grey lumps, with melting point of 1600 °C. Its trade name is Photophor for the incendiary use or Polythanol for the use as rodenticide. Its CAS number is [1305-99-3].

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On contact with acids or water, calcium phosphide releases phosphine, which ignites spontaneously.

Metal phosphides have been used as a means of killing rodents. A mixture of food and calcium 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 many of the common poisons have appeared. Other pesticides similar to calcium phosphide are zinc phosphide and aluminium phosphide.

Calcium phosphide is also used in fireworks, torpedoes, self-igniting naval pyrotechnic flares, and various water-activated ammunition.

During 1920's and 1930's, Charles Kingsford Smith used separate buoyant canisters of calcium carbide and calcium phosphide as naval flares lasting up to ten minutes.

It is speculated that calcium phosphide was an ingredient of some ancient Greek fire formulas.

Its safety and risk phrases are R15/29 R28 R50 (S1/2) S22 S42 S45 S61.

Calcium phosphide is a common impurity in calcium carbide, which may cause the resulting phosphine-contaminated acetylene to ignite spontaneously.