Zinc Phosphide

Phosphides of zinc were obtained by heating zinc chloride in a stream of phosphine, or by heating zinc with a salt-containing phosphorus on charcoal in a blowpipe flame.

Zn₃P₂ is obtained by heating an alloy of zinc and phosphorus in a crucible till no more phosphorus vapour is evolved. It can be freed from zinc by ignition in vacuo at 600° C., by treatment with mercury followed by volatilisation in a current of hydrogen at 400° C., or by fuming nitric acid, which dissolves the metal most rapidly. It has also been prepared by (a) strongly heating a mixture of zinc oxide, phosphoric acid, and carbon; (b) heating vaporised zinc and phosphorus in an atmosphere of hydrogen; (c) strongly heating zinc sulphide with a phosphate and carbon; (d) passing phosphorus vapour over melted zinc; (e) heating zinc and phosphorus under pressure.

It has been described as octahedral crystals of density 4.55 at 13° C., as prismatic crystals or needles, as a steel-grey crystalline substance, as compact, lead-coloured (losing its lustre in air), and of density 4.21 at 1.4° C., and as amorphous and pulverulent.

Zn₃P₂ can be distilled in hydrogen at about 1100° C. Hydrochloric and sulphuric acids act on it with the evolution of phosphine, and nitric acid dissolves it completely. The reaction

Zn₃P₂ + 6HCl = 3ZnCl₂+2PH₃

proceeds quantitatively.

When the above phosphide was heated at 400° C. in phosphorus vapour, a brownish mass remained that contained ZnP₂ mixed with unaltered Zn₃P₂. The dark coloured ZnP₂ was isolated by hydrochloric acid, which acted much less readily on it than on Zn₃P₂. It was not crystalline, and its density at 15° C. was 2.97.

Renault obtained fine needles of ZnP₂, varying from pale yellow to vermilion-red, by passing phosphorus vapour over zinc, zinc oxide, or zinc carbonate at a low red heat. ZnP₂ burns brightly in the air to zinc phosphate, and is rapidly attacked by nitric acid. Sulphuric acid has little or no action upon it. It begins to dissociate at 500° C. into phosphorus and Zn₃P₂.

The existence of ZnP and Zn₃P₄ is doubtful.