Calcium Monosilicide, Ca₂Si₂

Indications of the existence of another silicide have several times been observed. The formula Ca₃Si₂ has been ascribed to a compound obtained by heating together powdered silicon and calcium filings in the proper proportions at 1000° C. It seems probable, however, that the true composition is represented by the formula, Ca₂Si₂.

This compound gives spontaneously inflammable silicon hydride with dilute mineral acids, leaving a residue of hydrated silica. With concentrated acids there is a slow evolution of hydrogen. It is attacked by ammonia, and more readily by hot water than by cold. By heating with hydrogen, practically pure disilicide, mixed with calcium hydride, is formed. At 1050° C. the monosilicide, in the absence of air, dissociates into the disilicide and calcium.

The density of the monosilicide, mixed with a little uncombined silicon, is 2.346. The heat of formation is 166.3 Cal.