The surface and tribological chemistry of carbon disulfide as an extreme-pressure additive

The reaction of carbon disulfide with clean iron was investigated for temperatures between 623 and 776 K and pressures between 10 and 30 Torr. Film growth is limited by the thermal decomposition of CS2 at the growing interface and the activation energy for this process is 12.4 +/- 1.0 kcal/mol. The nature of the resulting film is analyzed using Raman and Mossbauer spectroscopies and by X-ray diffraction, where it is found that the film consists of a non-stoichiometric ferrous sulfide and also incorporates a carbide. This result is in accord with the tribological data where the interfacial temperature in the plateau region of a plot of seizure load vs. additive concentration is similar to 1460 K, the melting temperature of FeS. The seizure load increases substantially when the additive concentration exceeds similar to 2 wt.% of sulfur and, since carbide formation was detected in the film, this is ascribed to the formation of an iron carbide at higher additive concentrations. (C) 2000 Elsevier Science S.A. All rights reserved.