The lubricant sector is keen to embrace new technology and apply it in product applications where it makes economic and environmental sense—and one area of particular excitement is nanotechnology.
Nanomaterials possess specific properties at the nanometer length scale, roughly 1 to 100 nm, explains Mark T. Swihart, executive director of New York State Center of Excellence in Materials Informatics.
These could be colloids or powders of individual particles in that size range, but could also be larger materials with pores or other key property-determining features at the nanometer-length scale. Nanotechnology is the practical application of these properties and physico-chemical effects that arise from nanometer-scale features.
Today, applications range from microelectronic circuits to nanocapsule formulations of existing drugs and lubrication. Nanoparticles of zinc, titanium dioxide, graphite, silver and even diamonds can reduce wear and friction.
These materials have different properties within a lubricant, suggests Swihart. Although not all functions are yet understood, graphite (or graphene) nanoplatelets have low surface energy, which would provide lubrication by a sliding mechanism. A hard material like nanodiamonds, or a quasi-spherical material like fullerenes (buckyballs) or inorganic fullerene analogs, would more likely work by a rolling mechanism.
Materials like zinc and silver can also interact chemically with other components of the lubricant, and may prevent degradation of other components of the lubricant.
Reducing Friction and Wear
Dispersions of nanomaterials can be very stable and behave, for most practical purposes like homogenous liquids, waxes, or greases. However, at the nanoscale, hard inorganic particles can provide rolling lubrication or can modify the surfaces in contact with the lubricant in ways that small molecules and polymers cannot. They may have a local ‘polishing’ effect that reduces friction between parts.
Lorenzo Calabri is the COO at Italy-based Tec Star, which specializes in developing high-tech solutions for nanotechnology industrial applications. He says even a small concentration of nanoparticles could be sufficient to improve the tribological properties of a mechanical system.
When the load between the sliding parts is small, friction reduction is mainly ascribable to the bearing-like behavior of nanoparticles that roll between the contact surfaces, keeping their shape intact; for high-load conditions, a coating, induced by the presence of nanoparticles, is deposited on the crests of surface roughness and it can reduce direct contact between the asperities, and thus minimize wear.
Nanotechnology is an exciting field within lubrication primarily because there are no issues related to thermal and chemical degeneration over time and at increasing temperatures with inorganic nanoparticles.
Furthermore, those nanoparticles are [typically] inert, so [they are] without major issues about toxicity or other regulatory and life cycle issues. However, standard inorganic microparticles could not be used, as they are less effective than nanoparticles and are more dangerous from a mechanical point of view, behaving as a detrimental third body, which can eventually increase the abrasion of the parts in contact.
Tec Star’s anti-wear additive (AWA) nanolubricants are a family of additives for lubricants, which are made with “special onion-like nanoparticles,” the exact nature of which is proprietary. They work with greases and different type of oils (mineral, synthetic, esters, etc.) and have a range of applications in gears, gearboxes, engine, metal-working and cutting fluids.
Nanolubricants have been shown to produce an improvement in tribological performances strongly reducing the wear rate (43% reduction with respect to base mineral oil; 33% reduction with respect to commercial chemical added mineral oil; 80% reduction with respect with synthetic PAG oil) and improving the coefficient of friction behavior as well.
Other materials recently developed include a nanoformulated additive for lithium-based grease for mechanical parts in relative sliding motion, which is thought to decrease noise during sliding of mechanical parts.
Improving Engine Life and Energy Consumption
U.S.-based NanoTech Lubricants Inc infuses four to six nanometer-sized diamonds into oils through its additives, explains managing partner Michael Markovitz. Again, these act like ball bearings by transforming the sliding friction that normally occurs between metal surfaces into rolling friction, thereby substantially reducing friction, heat, wear and early oil failure.
This results in better oil life and fuel economy—if the oil runs cooler it burns off less—and a reduced engine’s wear. Nanotechnology can therefore increase engine life and reduce costs in the long-term.
However, Markovitz suggests, it is still early days for the widespread use of the technology within lubricants. Costs of the additives vary, but are offset by the fuel savings.
People don’t respond as fast as you’d expect, and I think that may be because they don’t want to take the risk—companies with 5,000 or even 500 engines are worried about trying something new, fearing it might cause damage. But seeing is believing, and this will change as more companies become aware of the benefits and, of course, the more expensive fuel becomes, the more open they will be to change.
Dr. Calibri agrees:
Global energy consumption is strongly related to energy dissipation in tribological contacts—improvements in this field are always [in demand], and nanomaterials are a very effective solution.
Some of their potentialities have already been demonstrated, but many others are still under investigation and need to be revealed. The use of nanotechnology in fluids and lubricants is only in its early stage, but is expected to explode in the close future.