# Synergistic Effects of CuO and ZnO Nanoadditives on Friction and Wear in Automotive Base Oil +
###### Abstract  
Efficient lubrication lowers friction, wear, and energy losses in automotive drivetrain components. Advanced lubricants are key to sustainable transportation performance, durability, and efficiency. This study analyzes the tribological performance of Group III base oil with CuO and ZnO nanoadditive mixtures. These additives enhance the performance of Group III base oils, making them highly relevant for automotive lubricant applications. An Optimol SRV5 tribometer performed ball-on-disk sliding contact tests with 100 Cr6 steel specimens subjected to a 50 N force and a temperature of 100 \({}^{\circ}\)C. The test settings are designed to mimic the boundary and mixed lubrication regimes commonly seen in the automobile industry. During the tests, the effect of nanoparticles on friction was measured. Microscopic wear analysis was performed on the worn specimens. The results demonstrate that adding 0.3 wt% CuO nanoparticles to Group III base oil achieves a 19% reduction in dynamic friction and a 47% decrease in disk wear volume compared to additive-free oil. Notably, a 2:1 CuO-to-ZnO mixture produced synergy, delivering up to a 27% friction reduction and a 54% decrease in disk wear. The results show the synergistic effect of CuO and ZnO in reducing friction and wear on specimens. This study highlights the potential of nanoparticles for lubricant development and automotive applications. t  
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with copper-based nanoparticles lies in their propensity for agglomeration within lubricant matrices, which can lead to unstable dispersions, increased abrasive wear, and potential lubrication system obstruction. Despite their efficacy in generating protective tribofilms, copper-based nanoparticles exhibit susceptibility to agglomeration within lubricant matrices, resulting in unstable dispersion, heightened abrasive wear, and potential obstruction of lubrication systems [7]. [PERSON] et al. [8] reported a 42.9% friction reduction and substantial wear improvement by dispersing 0.5 wt% of cylindrical CuO nanoparticles (35 \(\pm\) 5 nm) in SAE 20W-50 mineral oil with oleic acid used as a surfactant. This influential study inspired further research into nano-ball bearings and tribosintering effects while providing measurement standards for oxide nanoparticle effectiveness in lubricants. Moreover, advancements in manufacturing, such as sonochemical methods, have further improved nanoparticle synthesis. [PERSON] and [PERSON] [9] demonstrated that incorporating 0.1 wt% CuO nanoplatelets into 5W-40 synthetic oil reduced friction by 32%, with zeta potential results (92 mV) indicating stable dispersions. [PERSON] et al. [10] provided a comprehensive review of nanolubricant technologies involving metals, oxides, sulfides, carbons, and alloys, highlighting the individual strengths of CuO and ZnO in lubrication--such as tribofilm formation, nano-ball bearing effects, repair, and surface polishing. The findings indicate that CuO-ZnO hybrid additives can outperform single-component systems due to synergistic tribofilm and mending effects, but these hybrids require further experimental studies to address long-term stability and real-world performance. Later studies have added to this overall framework. For example, [PERSON] et al. found that CuO at 0.8-1.6 wt% lowers the coefficient of friction by 13-28% and ZnO at 0.6 wt% lowers it by 22%. These oxides roll, fix, polish, and form tribofilms [11]. Environmentally friendly ZnO nanoparticle synthesis is also advancing. [PERSON] et al. [12] showed that extract type, calcination temperature, and precursors affect nanoparticle shape and dispersion. When 0.5 wt% spherical ZnO (50-200 nm) from acetate was blended with vegetable oils, the optimum wear resistance and lowest friction coefficients were observed, underlining the crucial influence of synthesis conditions on tribological performance and the sustainability of lubricant formulations.