Molybdenum Disulphide, MoS₂

Molybdenum Disulphide, MoS₂, occurs in nature as molybdenite, but may also be obtained by the action of sulphur or hydrogen sulphide upon molybdic anhydride; by fusion together of sodium molybdate, molybdic anhydride, and sulphur; or by heating the sesquisulphide out of contact with air. A crystalline disulphide is conveniently obtained5 by heating together potassium carbonate, sulphur, and molybdenum dioxide or ammonium molybdate, and extracting the cooled mass with water; an amorphous form is obtained by heating together finely powdered ammonium molybdate and sulphur, and reheating the mass after the addition of a further quantity of sulphur.

Molybdenum disulphide is decomposed - yielding the sesquisulphide and molybdenum - only at the temperature of the electric furnace. It is attacked by chlorine, bromine, nitric acid, sulphuric acid, and, when strongly heated, by hydrogen or water-vapour, but not by alkalies. The specific heat of the naturally occurring molybdenite is 0.1067 (Neumann), and of the artificial, 0.1233 (Regnault).

The electrical properties and thermionic emission of molybdenite have been investigated; the mineral appears to exist in two states between atmospheric temperature and red heat, and at temperatures above 310° C. a characteristic emission of positive molybdenum ions occurs.