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Three kinds of protic ionic liquids with ammonium salts, dodecylamine salt of S-(1-carboxyl)-propyl- N, N-diethyldithiocarbamate (coded as DDED), dodecylamine salt of S-(1-carboxyl)-propyl- N, N-dibutyldithiocarbamate (coded as DDBD), dodecylamine salt of S-(1-carboxyl)-propyl- N, N-dioctyldithiocarbamate (coded as DDOD) were synthesized, characterized, and their tribological behaviors as additives in lithium complex grease were studied for steel/steel contact. The tribological properties were evaluated on an Optimol SRV-I oscillating reciprocating friction and wear tester and a MRS-10A lever-type fourball tester in details. The results of tests demonstrated that the novel additives were able to remarkably improve the extreme pressure, friction-reducing, and anti-wear properties of the base lithium complex grease when added at a low adding concentration (<3 %). Based on the performance comparison of three novel additives with different chain lengths in DTCs groups and a commercial additive with similar DTCs groups but no PILs groups, methylene bis dibutyldithiocarbamate (T323), a number of primary conclusions were drawn. The carboxylic acid ammonium salts, the typical function groups of the PILs existing in the molecule structures of three additives, could not only greatly enhance the physical and/or chemical adsorption on the metal surface to reduce friction of the base grease, and also have better synergism with DTCs groups in improving anti-wear performance of base grease. Based on the characterization and analysis of the worn surface by a PHI-5702 multifunctional X-ray photoelectron spectrometer (XPS) and a JSM-5600LV scanning electron microscope (SEM), a protective film consisting of FeS, organic compound was formed on the surface. The ordered adsorbed film and chemical reactive film on the sliding steels contributed to the main factor in improving the tribological properties of base lithium complex grease. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine the tribological behavior of amorphous overbased calcium sulfonate (AOBCS) and crystalline overbased calcium sulfonate (COBCS, transformed from the AOBCS) as additives in lithium complex grease. The transformation product of the calcium carbonate polymorph from AOBCS was calcite, as determined by Fourier transform infrared spectroscopy. Tribological properties were evaluated by an oscillating reciprocating friction and wear tester and a four-ball tester. The results showed that the addition of COBCS can dramatically improve both the antiwear performance and the friction-reducing and load-carrying properties of the base grease. However, improvement of the tribological properties of the base grease by AOBCS was highly dependent on the concentrations added and the loads applied. The tribological properties of the base grease were improved more by the addition of COBCS than by the addition of AOBCS. X-ray photoelectron energy spectrometry and thermogravimetric analysis revealed that both AOBCS and COBCS underwent complicated tribochemical reactions in the base grease and that chemically reactive films consisting of CaCO, CaO, iron oxide and organic compounds were formed on the worn surfaces. Taken together with the results of the tribo-tests, we suggest that transformation of the calcium carbonate polymorphs was the main factor in improving the tribological properties of lithium complex grease. The transformation of calcium carbonate polymorphs can broaden the application of AOBCS as an extreme pressure/antiwear additive in greases under boundary lubrication conditions. [ABSTRACT FROM AUTHOR]