Cobalt Phosphides

The phosphides of this metal are produced by similar methods. Co₂P has a maximum freezing-point of 1386° C., and the eutectic between this and the freezing-point of the pure metal is at 1022° C. and corresponds to 16.6 per cent, of phosphorus.

The combination of phosphorus with nickel was studied by Pelletier, Davy and Maronneau (loc. cit.), also by Lampadius and Berthier. The methods included heating reduced nickel in the vapour of PCl₃, heating copper phosphide and nickel in an electric arc furnace, the precipitation of a solution of the sulphate by nascent PH₃ derived from phosphorus and alkali. The thermal diagram of the nickel-nickel phosphide system showed a first eutectic on the nickel side at about 886° C. and 11 per cent, phosphorus. The first compound Ni₃P freezes at about 965° C., the second, Ni₅P₂, at about 1185° C. The compound Ni₂P crystallised from the melt in grey needles at about 1112° C.; it is insoluble in single acids, but is attacked by chlorine or fused alkali. This compound was also made by heating copper phosphide and nickel in an electric arc furnace and by several of the methods mentioned above. Ni₃P₂ and Ni₂P₃ have also been reported.

Some of the metals of the platinum group, including platinum itself, form phosphides. These alloys were investigated in a qualitative manner by Pelletier, Granger and others. The compound Pt₅P₃, formed by heating finely divided platinum with phosphorus at a white heat, was a white substance of metallic appearance, which lost phosphorus when heated, giving Pt₂P, and platinum when treated with aqua regia, leaving PtP. These compounds were insoluble in single acids and either slightly soluble or insoluble in aqua regia. The black precipitate produced by the action of PH₃ on PtCl₄ may be a hydrophosphide Pt(H₂P₂).