# Synergistic Effects of CuO and ZnO Nanoadditives on Friction and Wear in Automotive Base Oil +
###### Abstract
Research into nanoparticle synthesis techniques, such as electric discharge, has shown that key particle features directly impact tribological properties. [PERSON] et al. [13] found that smaller, oxidized CuO particles (23 nm, 54% oxide content) could reduce calcium-based grease friction from 0.028 to 0.0016, attributing this to enhanced tribofilm formation and greater surface adherence. These fundamental insights into the relationship between nanoparticle size, shape, and performance inform improvements in CuO-ZnO hybrid systems. Recent work by [PERSON] and [PERSON] [14] demonstrated CuO-ZnO mixed metal oxide nanoparticles (18-30 nm) in SAE 20W-50 lubricant at 0.5%, 1%, and 2% loadings. At 1%, the coefficient of friction and wear scar size were minimized, confirming synergy in tribofilm formation, surface repair, and nano-bearing effects. The addition of nanoparticles resulted in a significant reduction in friction and wear. The friction coefficient decreased from 0.119 for the base oil to 0.085 at a 2% nanoparticle concentration. Similarly, the wear scar diameter was markedly reduced from 1.744 mm (base oil) to 0.875 mm at the same level of nanoparticle loading. Notably, proper concentration optimization is key to suppressing agglomeration and maximizing performance. This study showed that concentration optimization is important for balancing performance improvement with agglomeration prevention. It also provided the first direct sign of the possibility of CuO-ZnO synergy. New studies on the features of metal oxide nanoparticles have helped to understand how they work in various conditions. [PERSON] et al. found that carbon nanotubes significantly increased viscosity in water-based fracturing solutions [15]. Nano-zinc oxide (1 g/L)and nano-copper oxide (10 g/L), on the other hand, made the fluids much more stable and thicker than blank fluids. They found that controlling the shape and dispersion of CuO and ZnO is important for making them work better as lubricants and ensuring their rheological and stability qualities are at their best in harsh fluid conditions. These findings support the idea that CuO-ZnO mixtures may be helpful for more than one thing, like making things better at rubbing together, staying stable at high temperatures, and having a thicker consistency. Discoveries in characterizing hybrid oxide materials have helped researchers understand how they can be used for multiple applications and how they can be mixed with other materials. [PERSON] et al. [16] reported that mixed materials made from modified cellulose and ZnO and CuO nanoparticles were better at insulating and had higher thermal stability than those with CuO only. Understanding how oxides and matrices work is crucial for making stable, high-performance nanolubricant formulations. To prove the idea of additive synergy, researchers have shown that nanoparticles, organic friction enhancers, and conventional additives can all work together. [PERSON] et al. [17] studied how nano-biochar interacted with popular oil additives like MoDTC (molybdenum dithiocarbamate), ZDDP (zinc dialkyldithiophosphate), detergent, and dispersant. They found that nano-biochar cut down on friction by 9.4% when mixed with antiwear additives and by 4.5% when mixed with friction-lowering additives. [PERSON] et al. [18] noted that 0.1-0.5 wt% nanoparticle additions (CuO or ZnO) improved tribological properties for all oil types studied, via rolling, polishing, mending, and coating production, while excessive CuO (2%) elevated friction. On the other hand, ZnO at 0.5 wt% had the opposite effect. Because they may be so helpful, composite and hybrid nanoparticles should be further investigated. This in-depth study adds to the scientific case for studying CuO-ZnO hybrids to maximize the benefits of both oxide types working together. Adding Zn and ZnO nanoparticles as extreme pressure (EP) additives in synthetic lubricants has substantially enhanced tribological performance under high-load conditions.