Calcium Phosphide, Ca₃P₂

Calcium Phosphide, Ca₃P₂, was first obtained in an impure form, probably contaminated with phosphate, by the action of phosphorus vapour on red-hot lime. Phosphorus and metallic calcium combine directly to give amorphous calcium phosphide.

Moissan obtained a red crystalline phosphide by the reduction of tricalcium phosphate by carbon in the electric furnace. It is a refractory substance only fused in the electric furnace. The density is 2.5 at 15° C. When heated in vacuo it slowly decomposes. Hydrogen and nitrogen have no action even at 900° C., nor boron, carbon, sulphuretted hydrogen, and ammonia at 700° C., but in the electric furnace phosphorus is replaced by carbon. Calcium phosphide is decomposed at once by water and dilute acids, giving phosphoretted hydrogen, but not by concentrated nitric and sulphuric acids in the cold. It burns brilliantly in oxygen at 300° C., giving lime and phosphorus pentoxide. Sulphur also reacts at 300° C. with considerable evolution of heat. Chlorine and bromine react vigorously at 100° C., and iodine at red heat, as also do the halogen acids in the gaseous state. There is a vigorous reaction with incandescence when the phosphide is heated with an oxidising agent such as potassium chlorate, dichromate, or permanganate. Absolute alcohol, ether, benzene, and turpentine have no action at ordinary temperatures.

Ignition of an intimate mixture of calcium phosphate and aluminium powder affords a rapid method for obtaining a source of phosphorus trihydride which is not spontaneously inflammable, and is only contaminated with a little hydrogen.