Lubricants are widely used to reduce the friction of mechanical parts, especially in mining, industrial, manufacturing and automotive spaces, and are essential for the protection of equipment/machinery from wear and degradation. Whilst many lubricants perform adequately, new formulations are always being developed to enhance lubrication performance and a useful lifetime.
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One of the most recent lubricants to emerge are long-life lubricants, which in theory do not require changing (however, this is debated by some). Another area that is evolving is the use of nanoparticles as an additive to reduce the friction between mechanical parts compared to conventional lubricants, and in this article we look at why these are looking ever more promising.
Lubricants are vital for any heavy-duty machinery, automobiles, or industrial equipment that uses mechanical parts. Lubricants provide a barrier between mechanical parts, which enables them to move over each other more smoothly with a reduced friction. Without lubricants, many of these mechanical parts would wear down and break very quickly, leading to a constant, and very expensive, changing of parts. Without lubricants there would be a high degree of friction between the solid components of a mechanical system, resulting in increased wear on the system and malfunctioning or breaking mechanical parts. Moreover, the movement of parts would be a lot more “clunky” without the addition of lubricants.
After all this time of lubricant development and production, why are nanoparticles being considered as an additive?
The inherent size of the nanoparticles is the short answer. In practice, nanoparticles suspended in lubricant formulations can penetrate the small gaps between two surfaces and change the tribological properties of the mechanical system. It is an increasingly reported area in academic literature and a wide range of nanoparticle sizes and compositions have been trialled, with the overall outcomes being a reduction in the friction and wear of mechanical systems.
The size of nanoparticles is one of the key benefits over other types of particle additives. Larger particles often fail in mechanical systems when trapped by filters, but nanoparticles have no such problem and can both pass through and occupy smaller gaps where larger particles cannot. Other benefits include a relatively high surface area, a high resistance to temperature (as many systems that lubricants are used in can get hot) and inertia to tribochemical reactions. In theory, these properties make nanoparticles a suitable additive for lubricant systems.
Whilst not yet attempted from a commercial perspective, the academic community has reported that the inclusion of nanoparticles in lubricants can reduce the friction coefficient by 25-50% compared to base lubricants. As it stands, all the friction reducing mechanisms of using nanoparticles are not known. However, those that are understood include the nanoparticles’ ability to form films allowing mechanical parts to slide over much easier, rolling effects where the nanoparticles act as ‘rollers’ for any mechanical parts that move over them, and reducing the amount of real contact between the mechanical parts (which is helped in part by the fact that nanoparticles have a high relative area to their size). The missing piece of the puzzle is how these effects work in unison to reduce the wear of the system.
Whilst many nanoparticles have been trialled, research has shown that the most promising results to date have come from either using copper nanoparticles or copper oxide nanoparticles in various base lubricants. Further research is required as some studies have shown that some nanoparticles have a detrimental effect on the friction and wear of a tribological system. Identifying the ideal nanoparticles for each application is key — especially as many different lubricants are used for different applications, and in many cases the lubricants are designed to work in specific systems.
Further work is required before nanoparticle lubricants are realized commercially; however, initial studies show that nanoparticles could help to reduce the friction and wear in tribological systems.
Sources:
- “Effect of nanoparticles as lubricant additives on friction and wear behavior of tetrahedral amorphous carbon (ta-C) coating”- Li X. et al, Jurnal Tribologi¸ 2018
- “A REVIEW ON EFFECT OF ADDITION OF NANO PARTICLES ON TRIBOLOGICAL PROPERTIES OF LUBRICANTS”- Patil S. J. et al, International Journal of Mechanical Engineering and Tribology, 2014
- Auburn University: http://www.eng.auburn.edu/~jacksr7/TLTjuly2015HamedGhaedniaNanoparticlesDryOnly.pdf
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