The future of anti-wear chemistry: Copper’s role in industrial lubricants

Years ago, while building a training deck for a lubrication certification course, I created sections on lubricant additive chemistry and oil condition monitoring that included elemental categories for additives. The certification body’s reference materials noted copper as a possible wear metal from brass or bronze components, a contaminant from copper flake anti-seize, and even as a potential additive in anti-wear formulations. 

I was intrigued, since I had never directly encountered copper used this way. My own research yielded little definitive proof. That changed recently at a technical conference, where I met Leyla Alieva, CEO and Founder of Neol Copper Technologies. She shared her company’s research on copper-based anti-wear compounds, and the results are strikingly promising. This article evaluates the state of research on copper compounds as lubricant additives, weighing the advantages and drawbacks of this approach.

Emerging research on copper-based AW and EP additives in industrial lubrication

Copper and its compounds, particularly copper oxides, salts, and nanoparticles, have drawn growing interest as potential anti-wear (AW) and extreme-pressure (EP) additives in lubricants. Traditional additive chemistries rely on zinc dialkyldithiophosphate (ZDDP), sulfur- and phosphorus-based EP agents, or molybdenum compounds.

Copper compounds offer different mechanisms, including the formation of protective surface films and nanoparticle “mending” effects. Despite these benefits, practical deployment has been limited by issues of stability, compatibility, and corrosion risk.

Alieva recommended a book to me that explored in depth the research of Dmitry N. Garkunov (Дмитрий Н. Гаркунов, often miswritten as “Garkumov”), who stands as one of the most influential Soviet and Russian tribologists of the 20th century. His research introduced and advanced the concept of “selective transfer,” also referred to as the wearlessness effect, which fundamentally reshaped the scientific understanding of friction, wear, and lubrication.

Garkunov helped pioneer the development of “metal-plating” lubricants, oils formulated with active metallic components such as copper to promote tribofilm formation during operation. These additive systems provided the elemental supply necessary for surface adaptation, making selective transfer more repeatable in real machines. He further contextualized selective transfer as a process of self-organization within tribosystems: during operation, contacts adapt chemically and structurally, moving toward a dynamic low-wear state. This insight prefigured modern interpretations of tribology as an emergent and adaptive discipline rather than one governed solely by degradation. Complementing this work, Garkunov investigated hydrogen wear (водородное изнашивание), showing that nascent hydrogen generated during friction could diffuse into metal lattices, embrittling them and accelerating wear. This was presented as the conceptual opposite of selective transfer: where one regime fosters protective films and stability, the other destabilizes surfaces and accelerates failure.

Working alongside I.V. Kragelsky and A.A. Polyakov, Garkunov demonstrated that under boundary-lubrication conditions – especially in steel-copper or steel-bronze systems with suitable lubricants – materials could self-form a thin, ductile, non-oxidized metallic film at the sliding interface. This tribofilm drastically lowered shear strength, sharply reducing wear and friction, and in certain regimes created what was described as “zero-wear friction.”

The practical implications of Garkunov’s research are substantial. Selective transfer demonstrated that near-zero wear is possible in machine components operating under boundary lubrication, provided the materials, lubricants, and conditions are favorable. This insight guided the design of anti-wear additives, surface finishes, and maintenance regimes aimed at extending machine life and reducing costs. However, his findings also emphasized the fragility of these states: changes in temperature, load, or lubricant chemistry could collapse the protective regime and revert systems to rapid wear.

Quantitative studies and later literature confirm the impact of his findings. Friction coefficients could be reduced by an order of magnitude, and wear rates diminished by factors of ten or more under selective transfer. Threshold values of load, speed, and temperature were catalogued for both the initiation of selective transfer and the onset of hydrogen wear, providing engineers with guidelines for application.

Evaluating copper additives in modern lubrication systems

Lubricant additives are essential to modern tribology, as they extend component life by reducing wear, friction, and seizure under load. Conventional AW and EP agents such as ZDDP, molybdenum disulfide derivatives, and sulfur-phosphorus compounds have served as the backbone of lubrication technology. However, these chemistries face both regulatory pressures, including phosphorus emission limits tied to automotive catalysts, and technical challenges such as volatility and thermal breakdown. Copper-based additives have been proposed as an alternative or supplement, with particular emphasis on nanoparticles and copper salts dispersed in oil or grease.

Mechanisms of Copper-Based Additives. Copper nanoparticles, including metallic copper, cuprous oxide (Cu₂O), and cupric oxide (CuO), have been shown to deposit onto rubbing surfaces, forming protective tribofilms that reduce metal-to-metal contact and decrease both friction and wear (Yu, Xu, Shi, & Chen, 2008; Rapoport et al., 2017). These particles may also serve a mending role by filling surface asperities, effectively smoothing worn areas. Their rolling or sliding behavior within the contact zone has been compared to micro-bearings, contributing further to wear reduction (Zhang, Li, & Cai, 2011). Copper salts such as copper oleate and copper stearate have also been studied. Unlike nanoparticles, soluble copper salts rely on thermal or chemical decomposition to produce copper-rich surface films capable of reducing wear under load (Liu et al., 2012).

Advantages of Copper Additives. Research indicates that copper-based additives can improve lubricant performance in several ways. Laboratory tests have consistently shown that the addition of copper nanoparticles at low concentrations reduces wear scar diameters, particularly in ASTM D4172 four-ball wear experiments (Yu et al., 2008). Copper compounds can also enhance load-carrying capacity in EP evaluations, with four-ball weld load tests confirming higher seizure resistance when CuO nanoparticles are present (Zhang et al., 2011). Synergistic effects have been reported when copper nanoparticles are combined with traditional chemistries such as ZDDP or sulfurized additives, suggesting that hybrid formulations may achieve a balance between reactive film formation and structural reinforcement of tribofilms (Rapoport et al., 2017). Beyond these performance enhancements, the unique mechanisms of copper—including mending and film deposition—represent a conceptual departure from conventional sulfur and phosphorus pathways, potentially offering alternatives in markets where regulatory pressures demand new solutions.

Drawbacks and Challenges. Despite these advantages, copper-based additives pose several well-documented challenges. Copper ions are highly reactive and can accelerate corrosion of yellow metals such as brass and bronze, which are widely used in mechanical systems. To counteract this risk, formulations often require co-additives such as benzotriazole or mercaptobenzothiazole as metal deactivators (Campen, Green, Lamb, & Spikes, 2005). Dissolved or particulate copper also acts as a strong oxidation catalyst, increasing the risk of sludge and varnish formation in oils during long-term service (Campen et al., 2005). From a formulation standpoint, nanoparticles are inherently unstable in oil matrices and tend to agglomerate or sediment, raising concerns about storage and long-term performance. Achieving stability typically requires dispersants or surface functionalization, which adds complexity to additive package design (Liu et al., 2012). Copper salts may also interact unfavorably with other lubricant components, destabilizing detergents, dispersants, or antioxidants. For these reasons, commercial adoption of copper-based additives remains limited, with most applications confined to laboratory studies or niche specialty greases.

Practical Considerations. If copper compounds are considered for formulation, the inclusion of effective metal deactivators is essential to avoid corrosive attack on system components. Testing protocols must extend beyond traditional wear and EP evaluations to include oxidation stability and corrosion assessments. Standardized methods such as ASTM D4172 for wear, ASTM D2783 for EP, ASTM D943 and ASTM D2272 for oxidation stability, and ASTM D130 for copper corrosion provide a framework for evaluating candidate formulations. Given the current limitations, copper-based additives may be best suited for highly specialized applications, such as aerospace systems or specialty greases, where unique operating conditions and performance priorities justify the added complexity.

Future Outlook: Where Copper Additive Technology Fits in Industrial Lubrication

Copper compounds hold considerable potential as AW and EP additives due to their unique mechanisms, including nanoparticle mending effects and tribofilm deposition. They can enhance wear resistance, improve load-carrying capacity, and exhibit synergistic interactions with established additive chemistries. Nonetheless, their widespread adoption is hindered by challenges related to corrosion, oxidation catalysis, and dispersion stability. Future progress will depend on the development of novel surface functionalization strategies, hybrid additive systems, and application-specific deployment. At present, copper compounds remain promising research candidates but are not yet mainstream commercial solutions in lubricant additive technology. Perhaps the work being done by Leyla Alieva will change that.  

References
Campen, S., Green, J. H., Lamb, G. D., & Spikes, H. A. (2005). In situ studies of model antiwear lubricant films. Tribology Letters, 19(1), 7–11.  
Liu, G., Li, X., Qin, B., Xing, D., Guo, Y., & Fan, R. (2012). Investigation of the mending effect of copper nanoparticles on a tribologically stressed surface in lubricating oil. Wear, 252(3–4), 342–348. https://doi.org/10.1016/S0043-1648(01)00858-2
Rapoport, L., Leshchinsky, V., Lvovsky, M., Popovitz-Biro, R., Feldman, Y., & Tenne, R. (2017). Tribological properties of WS₂ nanoparticles under mixed lubrication. Tribology Letters, 23(3), 185–190.  
Yu, H., Xu, Y., Shi, P., & Chen, J. (2008). Tribological properties and lubricating mechanisms of Cu nanoparticles in oil. Tribology Letters, 32(3), 193–202.  
Zhang, M., Li, W., & Cai, R. (2011). Friction and wear characteristics of CuO nanoparticles as lubricant additives. Tribology International, 44(4), 426–433.