The system Os–Mo–S

Abstract

Phase relations in the system Os–Mo–S were studied in a 1000°C isothermal section by the technique of evacuated silica glass tubes. Molybdenite forms stable assemblages with erlichmanite (OsS2) and osmium, whereas Mo2S3 coexists with Os, Mo and Mo–Os alloys. Experiments aimed at the determination of the solvus between MoS2 and OsS2 were conducted at temperatures in the range 600–1200°C. Molybdenite dissolves 0.24 and <0.2 at.% Os at 1200°C and 1000°C, respectively; below 1000°C, the Os content is below 0.1 at.%. Concentrations of Os in natural molybdenite are extremely low, on the order of ppb, and therefore are extremely unlikely to reach the experimentally established limit of solubility. Erlichmanite is stable in the stability field of pyrrhotite, which corresponds to a geologically common activity of sulfur. Therefore, Os is expected to be bonded to sulfide under the same conditions under which molybdenite occurs in nature.