All conventional lubricants borne of classic hydrodynamic theory are designed to provide lubricity. Inherent in the desire to provide lubricity to mechanical systems is the desire to protect the interacting metal surfaces from wear. Much effort in tribology is dedicated to engineering anti-wear (AW) additives, often designed to curb excessive wear by coating surface asperities with sacrificial metallochemical compounds that facilitate easier shearing at the frictional interface. Alternatively, hard AW coatings such as detonation nanodiamond (DND) and diamond-like carbon (DLC, a/k/a tetrahedral amorphous carbon – TaC), seek to protect the underlying metal surfaces by means of seemingly impenetrable barriers. Regardless of the methods employed, the mission of all conventional hydrodynamic lubricant formulations remain the same; protection of the metal interacting surfaces.
Anti-wear technologies are actually counterproductive and obsolete
Conventional anti-wear protection of interacting mechanical friction surfaces is counterproductive. Wear, the demonized enemy of hydrodynamic lubrication, is actually its savior in disguise. Explained simply, tribological efforts at preservation of the underlying metal are, necessarily and unavoidably, efforts in the preservation of undesired friction; as the asperities present on all such metal surfaces are the root cause of friction. Said otherwise, protection of metal parts is, unfortunately and undesirably, corresponding perpetuation of the friction that hydrodynamic lubrication seeks to overcome. If the viscosity of lubricants is increased to overcome the mean height of surface asperities (increased ratio of lubricant film thickness to root mean square (RMS) surface roughness, known as lambda according to the following equation: λ = h/σ), the lubricant itself then becomes an additional source of friction due to reduced fluidity. True lubricant laminar flow at the nanoscale is unattainable in the presence of surface asperities. Asperities on the surface of lubricated parts cause nanoscopic turbulent flow dynamics, resulting in induced stall regions and expanding vorticies that contribute macro-scale friction to lubricated mechanical systems. In order to achieve maximum efficiency in any lubricated mechanical system, surface asperities must be removed; this means carefully engineered and purposeful surface wear must occur.
Desirable and productive surface wear through nanopolishing agents
ISN technologies seek to accomplish this controlled and desirable polishing wear of metallic friction surfaces as the hydrodynamically lubricated mechanical systems in which they are employed operate normally. Asperities are thus removed slowly and safely over time. The early – commercially unfeasible – embodiments of ISN technology used complex, externally added, nanopolishing agents in the lubricants. These lab-synthesized nanoparticles took the form of known hard and abrasive compounds such as alumina, silica, ceria, titania, nanodiamond, cubic boron nitride and molybdenum oxide. Some of these early nanopolishing agents were paired with additional layered planar microparticles (such as graphite, hexagonal boron nitride, molybdenum disulphide and even soft magnesium silicates), in an attempt to further enhance the underlying metal’s surface morphology via filling of asperity valleys; this filling of asperities imparting some of the physical properties of greater surface smoothness, above and beyond any true nanopolishing effect had from the abrasives portion alone. Much of the difficulty in implementation of these early ISN attempts came in the complexity of the synthesis methods for the nanoparticles, coupled with the need to correctly determine the exact (efficacious) ratio of of such particles to their liquid lubricant suspension media. Of equal difficulty was identifying the exact size of the nanoparticles necessary to most effectively accomplish the polishing effect. Two pioneers in ISN theory, Dr. Mohsen Mosleh, and Dr. Khosro Shirvani, opined that the optimum diameter of nanopolishing agents (dubbed Surface Conditioning Nanoparticles – “SCN”) should be no more than half the Rave value of the surface to be polished.
In Drs. Mosleh and Shirvani’s experiments, this optimum polishing agent diameter was calculated to be 35 nm, based on an average Rave of 100 – 200 nm for most common automotive engine parts. Dr. Mosleh’s chosen “SCN” abrasives took the form of nanodiamond, aluminum oxide, silicon oxide, boron carbide, silicon carbide and zirconium oxide; all chosen for a hardness ≥ 7 Mohs.
In situ synthesis (ISS) of nanopolishing agents: ISN’s quantum leap forward
Latter commercially-viable ISN technology efforts took the form of in situ synthesized nanopolishing agents, formed ad hoc inside the lubricated mechanical system as, and exactly where, needed. This in situ synthesis (ISS), (ISN) technology, made use of the (nanoscale) extreme heat of asperity tip interactions (nano/micro-welding), to form surface-graphitized abrasive nanoparticles (SGANs) from carefully chosen liquid chemical precursors added to the circulating lubricant. As these chemicals circulated using the lubricant as their carrier, they underwent pyrolysis during the nanoscopic plasma events occurring during violent asperity tip collisions; these chemical reactions yielding graphene that encapsulated the newly generated molten metal third-body wear particles into solid, abrasive, endohedral metallofullerenes. This ISS/ISN technology was later (and is now currently), commercially marketed as Phantaslube® molecular nanopolishing lubricant additive.
These (Phantasmene™) spherical SGANs have diameters dictated by the size of the removed asperities that formed them; this is to say that the earlier problems associated with determining the optimum diameter of ex situ nanopolishing particles are now solved by allowing the friction event itself to control the size of the nanoparticle necessary to defeat it. These SGANs then cut through remaining surface asperities, leaving ploughing plastic deformation wear channels in their wake, polishing the surfaces of metal to near atomic-level perfection (Rave values in the low single-digit nm range, approaching zero – see interferometer image at the top of page), while concurrently surface hardening the metal below due to the compressive forces involved in creating the wear channels. As a tribological bonus, additional graphene synthesized in the pyrolysis reaction is allowed to circulate in the lubricant as a coating and heat-transfer agent; this, the most effective (lowest mass/highest surface area) heat-transfer agent currently known to mankind. As these SGANs themselves become abraded and shed graphitic layers, they reduce in diameter to a final form believed to be 1.2 – 1.5 nm in diameter.
As these SGAN endohedral metallofullerenes contain metal oxide cores, they exhibit ferromagnetism and stick to the metal surfaces as permanent nanobearings, preventing future metal-to-metal contact between parts and imparting as close to a superlubric state (friction coefficients estimated around 0.01) as may be possible to achieve in any real-world mechanical system.
ISN technology’s revolutionary tribological results
The surface profile data image at top illustrates ISN’s ability to produce friction surface Rave values in the low single-digit nm range (Rave < 4 nm, RMS < 5 nm). Dr. Jay Narayan, another early ISN pioneer, reported ISN-induced reduction of friction coefficients in his vehicle test engines to levels of CoF 0.01. Dr. Narayan also recorded maximum fuel efficiency gains of 35%, with maximum 90% reductions in carbon emissions from test vehicle engines. Dr. Mosleh’s surface conditioning nanoparticle (SCN) results were somewhat less astonishing. Dr. Mosleh measured his SCN-induced surface smoothening results to be between 6 – 8% improvement, depending on the metallic engine part analyzed.
The Author’s ISS-ISN test results have been a bit more shocking. Phantaslube® ISS-ISN technology has reported anywhere from 10 – 50% improvements in fuel economy in on-road, real-world testing. Recent over-the-road (OTR) semi truck testing yielded a reported 21.5% improvement in fuel economy during a 1,200+ mile, 8 U.S. state, evaluation run. Further, detailed interferometer data of the surface profile of a treated engine part showed a 6,000+% improvement in surface smoothness (initial Rave = 221.6 nm to final Rave = 3.4 nm), a corresponding 99% reduction in asperity heights. Naturally, such advancements in surface perfection open a host of new doors in engineering possibilities, as the resulting massive increases in actual contact area of interacting metal parts (approaching designed “nominal” surface areas) mean markedly increased load carrying capacities; these hugely increased contact areas imparting near unlimited longevity to any so-lubricated mechanical system. It is important to note that modern tribological science reveals that < 2% of the nominal metal contact area is ever in actual contact with its corresponding interacting surface due to the presence of asperities. Further, real-world performance of ISS-ISN lubricated systems, over time, show that engines utilizing this new lubrication approach begin to attain design (perfect-world) maximums.
Under this new ISN lubrication paradigm, we tribologists are now forced to recognize surface “wear” (albeit engineered and purposeful) as friend rather than evil foe.
Credit for images: Used by permission of Phantaslube LLC, a Peerless Worldwide company. Interferometer data courtesy of Zygo Corporation, an AMETEK company.
The Author declares a competing personal/employment financial interest in Phantaslube LLC and its patented Phantaslube® molecular nanopolishing lubrication technology, as the inventor of such ISS-ISN (SGAN) technology, and the CEO of Phantaslube LLC and its parent company, Peerless Worldwide, LLC, the assignee of the relevant Patents.
Dr. Rick Shankman, ACS APS AIChE MIET is the CEO at Phantaslube LLC, maker of patented Phantaslube® (nontoxic, graphene-based) molecular nanopolishing lubricant technology. Dr. Shankman's research also includes the bottom-up reflux synthesis of graphene from simple carbonaceous precursors and subsequent hydrophobic self-assembly of large area graphene films on the surface of water.