Robust Interfacial Tribofilms by Borate- and Polymer-Coated ZnO Nanoparticles Leading to Improved Wear Protection under a Boundary Lubrication Regime

Abstract

This work reports on the development of borateand methacrylate-polymer-coated zinc oxide nanoparticles (ZnOBM) via a plasma polymerization technique to replace the harmful conventional antiwear additive zinc dialkyl dithiophosphate (ZDDP) in automotive lubricants. Here, the tribochemistry across the interfaces formed between sliding ferrous surfaces and coated and uncoated ZnO nanoparticles is thoroughly studied from the perspective of elucidating the tribofilm formation, wear, and friction performance of a novel ZnOBM-based nanolubricant. Tribological tests conducted under a boundary lubrication regime revealed that oil formulations containing only ZnOBM nanoadditives and a mixture of ZnOBM with a low amount of ZDDP (350 ppm of P) significantly improve wear performance (up to 95%) compared to the base oil. Electrical contact resistance results acquired in situ during tribological tests demonstrated that lubricants containing ZnOBM nanoparticles at sliding interfaces undergo tribochemical reactions to form stable tribofilms that reduce friction and wear. Atomic force microscopy (AFM), X-ray absorption near-edge spectroscopy (XANES), and X-ray photoelectron spectroscopy (XPS) analysis revealed that ZnOBM nanoparticles, by themselves, form patchy interfacial tribofilms containing iron borate, boron oxide, and zinc oxide and lead to superior tribological performance. Interestingly, ZnOBM nanoparticles interact synergistically with ZDDP to form a hierarchical interface of boron-doped tribofilms, with zinc−iron polyphosphates at the surface and iron oxide, zinc and iron sulfides in the bulk. These encouraging results suggest the potential effective use of the ZnOBM nanoparticles to significantly reduce harmful levels of ZDDP (350 ppm) in the engine oil without compromising the antifriction and antiwear performance and to develop eco-friendly high-performance lubricant additives.

Anisotropic growth of ZnO nanoparticles driven by the structure of amine surfactants: the role of surface dynamics in nanocrystal growth

“…Note that this peak is much more important in the case of C 12 -NH 2 than for C 12 -NH(CH 3 ) (Figure S10a,b, respectively) which substantiates that the acid-base reaction is more effective for primary amines and suggests that oligomerization occurs only in this case. This result was confirmed by 13 13 C CPMAS signal is observable stating that such molecular species remain small and exhibit high mobility, which assert that they are not oligomers. After 28 days, these signal just slightly increase and only very weak 13 C CPMAS signals could be detected.…”

“…This result was confirmed by 13 13 C CPMAS signal is observable stating that such molecular species remain small and exhibit high mobility, which assert that they are not oligomers. After 28 days, these signal just slightly increase and only very weak 13 C CPMAS signals could be detected. Thus, while both primary and secondary amines lead to Zn amido complexes, a notable difference is observed between primary and secondary amines: secondary amines are too hindered and only primary amines form oligomers.…”

“…These amines of identical aliphatic chain-length were mixed with a zinc precursor to get ZnO NCs of very different morphology: either 2D defined nanorods, or isotropic spherical nanoparticles, or shapely ill-defined aggregates. In the course of nanoparticles formation, we analyzed at each step of the synthesis both experimentally by multinuclear NMR ( 1 H, 13 C, 17 O) [58][59][60][61][62][63][64] and theoretically by DFT modeling the role of the amine, including pertinent surface dynamics. We evidenced the key role of weak interactions as lever for the control of the NCs final morphology, with in the case of ZnO NCs a decisive role of H-bonding network during the hydrolytic process in the presence of primary amine surfactants that results in two dimensional-defined nanorods formation.…”

Ball Milled Graphene Nano Additives for Enhancing Sliding Contact in Vegetable Oil

“…Wear mainly occurs in the boundary and mixed lubrication regimes during conditions of transient state (i.e., start-up and shutdown), high load, and low-speed operation [9,10]. In the boundary lubrication regime, direct contact between lubricating surfaces commonly occurs even though a fluid is present.…”

XANES Study of Tribofilm Formation With Low Phosphorus Additive Mixtures of Phosphonium Ionic Liquid and Borate Ester

“…The poisoning of automobile catalytic converters by volatile phosphorus species in the engine oil has fueled the research to develop low phosphorus engine oils by reducing or replacing the current phosphorus-containing additives (Williamson et al, 1985;Rokosz et al, 2001;Kröger et al, 2006;Zhang et al, 2017;Khare et al, 2018;Sharma et al, 2019b;Vyavhare et al, 2021b). Since 1988, the amount of phosphorus in engine oil is on a downward trajectory (Spikes, 2004), and recently the international lubricant standardization and approval committee (ILSAC) has introduced the GF-6 performance standards which limits the phosphorus concentration in engine oils to 800 ppm maximum (Anand et al, 2015).…”