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Phosphides are compounds of phosphorus with another element.
The most important of the phosphides falling here are obtained by direct action of the constituent elements; they include :(1) Copper phosphide (cuprophosphorus, phosphor copper). Produced in a reverberatory furnace or in a crucible. Usually in yellowish‑grey masses or in small, very brittle ingots of crystalline structure. The heading covers copper phosphide and master alloys of copper only if they contain more than 15 % by weight of phosphorus. Under this limit they fall generally in Chapter 74. Copper phosphide is a very good deoxidiser of copper, increasing the hardness of that metal; it improves the fluidity of molten metal, and is used in the manufacture of phosphor bronzes. (2) Calcium phosphide (Ca3P2). Small chestnut‑coloured crystals or grey granular masses which, on contact with water, give off hydrogen phosphides which ignite spontaneously. Used with calcium carbide for naval signals (self‑igniting flares for buoys). (3) Zinc phosphide (Zn3P2). Grey, poisonous powder with a vitreous fracture; gives off phosphine and deteriorates in moist air. Used for destroying rodents and locusts, and also in medicine (instead of phosphorus). (4) Tin phosphide. A very brittle silvery‑white solid. Used in making alloys. (5) Other phosphides, e.g., hydrogen phosphides (solid, liquid, gaseous), and the phosphides of arsenic, boron, silicon, barium, cadmium. This heading excludes : (a) Compounds of phosphorus with oxygen (heading 28.09), with halogens (heading 28.12) or with sulphur (heading 28.13). (b) Platinum and other precious metal phosphides (heading 28.43). (c) Ferrophosphorus (iron phosphide) (heading 72.02).
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