Effect of base oil polarity on the micropitting behaviour in rolling‐sliding contacts

Abstract

An automated micropitting test rig that uses the proven three‐point contact configuration was applied to study the effect of base oil polarity on micropitting behaviour in rolling‐sliding contacts. The tribological tests using one polar (ester) and one non‐polar (polyalpha olefin [PAO]) base oil mixed with four different additives were first done in a micropitting rig to study the friction, wear, and micropitting performance. The tested specimen after tribological tests were examined by an optical microscope to study the micropitting on the surface. The X‐ray photoelectron spectroscopy (XPS) was applied to obtain the related tribochemical information from the reaction layer. The results showed that higher wear and less micropits formed when testing with ester‐based lubricants. This was related to the higher affinity to the steel surface of polar base oil molecules that can compete with additives to attach to the surface, resulting in a thinner reaction layer and shorter chain phosphates.

Influence of Base oil Polarity on the Tribological Performance of Surface-Active Engine Oil Additives

“…Our ToF-SIMS data shows PAO surface to be covered by relatively higher concentration of long chain metaphosphates than in ester oil. The results are in agreement with Cen et al [55] who found phosphate chain length of ZDDP tribo lm to be longer in PAO than in ester based oil. It is also known that short chain phosphates and consequent nanocrystallization generally contributes to a resilient tribo lm than reaction layers formed of longer chains [50].…”

“…It is also known that short chain phosphates and consequent nanocrystallization generally contributes to a resilient tribo lm than reaction layers formed of longer chains [50]. Further, the tribo lms formed by short chain phosphates are shown to be harder than those formed by the overlying long chain phosphates [55,62]. With increase in hardness there can be a decrease in both the adhesive and deformation components of the measured friction coe cient [63].…”

“…Contrary to friction measurements, no direct correlation could be established relating base oil polarity and wear performance. It is known that formulations based on ester oil show higher wear compared to those based on non-polar oils [32,33,55]. In the present study we have used an ester oil of high non-polarity index (NPI =214) which may be the reason for the lack of correlation between base oil polarity and wear.…”

Superlow Power Consumption Memristor Based on Borphyrin–Deoxyribonucleic Acid Composite Films as Artificial Synapse for Neuromorphic Computing

“…In contrast, the P 2p spectra of the ZnTCPP/ LSMO/STO only had one peak centered at 140 eV, which corresponds to Zn 3s. 43,44 The above results confirmed the successful formation of ZnTCPP and ZnTCPP−DNA films. Figure 1e,f show the measured I−V curves of the ZnTCPPand ZnTCPP−DNA-based devices, respectively, for 50 cycles of the 0 → 3 → 0 → − 3 → 0 V DC voltage sweep mode.…”

“…These can be attributed to P 2p 3/2 in PO 4 3– of the DNA backbone, P 2p 1/2 in the phosphorus of sodium phosphate, and Zn 3s in ZnTCPP, respectively. In contrast, the P 2p spectra of the ZnTCPP/LSMO/STO only had one peak centered at 140 eV, which corresponds to Zn 3s. , The above results confirmed the successful formation of ZnTCPP and ZnTCPP–DNA films.…”