Action mechanism of 35S-containing antiwear and EP additives

Antiwear and extreme-pressure additives labelled with ³⁵S were synthesised by reacting ³⁵S₂Cl₂ with isobutylene and treating the adduct with potassium xanthate, or by labelling the unlabelled compound with elemental ³⁵S in boiling carbon di-sulphide. Static adsorption tests of the labelled additives on iron or copper specimens show an adsorption increase with temperature. The data are in good agreement with the results of thermal analysis of the additive as such or mixed with iron or copper powder. The behaviour of the oil solutions containing labelled additives on a friction machine emphasised the formation of superficial layers on a metallic surface containing the reaction products of the additive decomposition compounds with the metal. The thickness of these layers remains nearly constant during the test but increases with normal load. Pyridine washing of the specimens removes adsorbed layers whereas chemisorbed layers remain on the metallic surface.