Calcium Silicide, CaSi₂

Calcium Silicide, CaSi₂, was first obtained by Wohler, by heating together a mixture of calcium chloride, metallic sodium, and sodium fluosilicate or crystallised silicon. It may be prepared by heating together in the electric furnace, lime or calcium carbonate with quartz and coal, lime and silicon, calcium chloride and silicon, lime and silicon with the addition of calcium fluoride or chloride, by direct combination of metallic calcium with silicon, or, finally, by heating together calcium hydride and silicon at 1000°- 1010° C. in an atmosphere of hydrogen.

Calcium silicide forms a grey crystalline mass with a metallic lustre, and of the hardness of quartz. Its heat of formation is 208.7 Cal., and its density is 2.5. It is unaffected by hydrogen at red heat, but readily attacked by halogens. It is slowly attacked by water giving calcium hydroxide, silica, and hydrogen. With hydrofluoric acid it becomes incandescent. When exposed to the air it is slowly oxidised, forming silica and lime. Concentrated hydrochloric acid reacts with it, giving a silicone, Si₃H₃O₂, but with the dilute acid, hydrogen silicide is obtained, whilst alkalies produce pure hydrogen.

Goldschmidt proposed the use of a mixture of calcium and calcium silicide in thermite reactions. If calcium silicide be added to a molten bath of iron or steel it acts as a deoxidising agent, and, owing to the heat of the reaction, as a reheater.