Lubrication antagonism mechanism of nano-MoS2 and soot particles in ester base oil

Abstract

Spherical nano-MoS2 (S-MoS2) has excellent lubricating properties and potential application value in engine oil additives. Engine soot can enter the engine oil, so the tribological interaction between S-MoS2 and diesel combustion soot (DCS) should be investigated. In this study, DCS was used to simulate engine soot. The interaction was investigated in dioctyl sebacate (DOS), and the interaction mechanism was full characterized. Results showed that S-MoS2 and DCS had obvious antagonism effects on lubrication. The 0.5% S-MoS2 exhibited good lubricating properties in DOS, which could reduce friction by ∼22% and wear by ∼54%. However, after 0.5% S-MoS2 was added to the 0.5% DCS contaminated DOS, the lubrication performance was not improved and was even worse than that without S-MoS2. When S-MoS2 was added for DOS lubrication, a tribofilm containing MoS2 formed on the friction surface, but simultaneously adding 0.5% DCS resulted in the disappearance of the MoS2 tribofilm. Moreover, under the action of friction heat, DCS and S-MoS2 could form hard MoxCy, thereby increasing abrasive wear. Finally, a preliminary deantagonism method was provided. After 2.0% zinc isooctyl dithiophosphate was added to the above antagonistic system, the friction coefficient did not show visible changes, but the wear recovered to a level close to that when only S-MoS2 was added. The antiantagonism method is not very satisfactory and some more efficient methods need to be further explored.