Ionic Liquids Based on Chromotropic Acid: Excellent Lubricating Additives for Aqueous System

In this paper, four ionic liquids based on chromotropate (CAILs) were prepared and applied to heighten the tribological performance of aqueous system on different metal friction contacts. Taking for the potential choice for water-based lubricating additive, CAILs exhibited excellent water solubility and corrosion resistance. Tribological results showed that the CAILs, especially the phenolic hydroxyl group decorated samples (TsnN4444 and TsnP4444), demonstrated extremely effective lubricating properties with the efficient friction and wear descent (69% and 83% for Fe, 47% and 94% for Cu, 74% and 69% for Al, respectively). Especially, the excellent load-carrying capacity was also presented with the highest PB (833N) and PD (1568N) values for TsnP4444. It is speculated that the CAIL molecular adsorption on the interface and further generation of tribochemical films are beneficial for their lubricating effects. resulting from the systematic discussion and analysis of CA, QCM, SEM, XPS, and FIB-TEM tests. However, TsN4444 and TsP4444 showed less effective lubricating performances and poor load-carrying capacities due to tribocorrosion of hydroxyl groups at the interface.

Frictional Behavior of Boundary Lubricated Contacts: Effect of Tribochemical Surface Films

The friction characteristics of lubricated contacts are usually determined by the shearing of three interfacial structural elements; namely lubricant fluid film, tribochemical reaction films and the near-surface materials. The shear behavior of the fluid film components of lubrication can be adequately described by either the hydrodynamic, or elastohydrodynamic theories and calculations. The shear behavior of the near surface materials can also be approximated by contact mechanics. However, due to the complexity and lack of adequate information, description and analysis of the tribochemical film contributions to frictional behavior is more challenging. In this study we present evaluation of the friction behavior of a lubricated contact as a function of tribological test duration, as the tribochemical surface films were being formed. Tests were conducted with two different formulated lubricants, in addition to an unformulated PAO basestock lubricant. One of the formulated lubricants consists of PAO synthetic basestock with 2.5% each of ZDDP and MoDTC additives. The other formulated lubricant is a fully formulated commercial gear oil with similar viscosity. During the friction tests in a fully flooded reciprocating sliding roller-on-flat contact configuration, the friction coefficient decreased exponentially as the tribochemical films were formed; highlighting the impact of boundary films on friction. In the test with the basestock fluid, the friction remained constant for the duration of the test; although an oxide layer was formed. Nanoindentation hardness and modulus measurements were conducted on two of the tribochemical films to measure their mechanical properties and the consequent impact on measured friction during testing.