Formation of FeS Tribofilm from Unsymmetrical Disulfides as Effective Extreme Pressure and Antiwear Additives

Abstract

Sulfur-based additives have excellent extreme pressure (EP) performance. However, a high amount of sulfur causes metal corrosion. The non-corrosive and ashless organo-disulfides have been synthesized via Bunte salt method. The unsymmetrical dodecyl octyl disulfide (DDODS) with good oil-solubility provides better EP and anti-wear (AW) properties. The DDODS shows outstanding EP value (1961 N) and small WSA (9 mm²) in naphthenic base oil (NBO), respectively. This performance is superior compared to symmetrical didodecyl disulfide (DDDS). The outstanding performance of DDODS is due to the good solubility in NBO and the formation of a sulfur film on the metal surface. The formation of iron sulfide (FeS) under EP conditions provides excellent tribofilm compared to iron (III) oxide (Fe2O3) and iron sulfate (FeSO4).