Finished Lubricants

Nanotechnology’s Leap

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After nearly 30 years of study, nanoscale lubricants are ready to step out of university and government research labs and make their way into wider applications. At least that was the message conveyed by numerous presenters and exhibitors at the Society of Tribologists & Lubrication Engineers annual meeting last month.

Around 1,500 people gathered in Orlando, Fla., for the event, and many were focused on what occurs when measurements fall below 100 nanometers (or one-millionth of a meter). Of the more than 500 technical papers offered, fully 10 percent were devoted to solving puzzles at such microscopic levels. Attendees could hear about nanoparticles and nano-additives, nanofillers for nanopores, nanomanipulations, nanomechanisms, nanolaminates, nanopackets, nanofilms, nanostructures, nanocomposites, nanofluids and more.

Fabrice Dassenoy of the Ecole Centrale de Lyon in Ecully, France, acknowledged the steep challenges of producing and optimizing these tiny spherical and tube-shaped materials, and asserted that science is close to cracking the nano mystery. The key thing is that lubrication by nanoparticles is a reality, and it will be a good alternative in the near future, he said.

Dassenoy described the step-by-step progress made by AddNano, a European consortium dedicated to pushing nanolubricants out to the mainstream. With a budget of E12 million, largely funded by the European Commission, AddNano started up in October 2009 and is managed by the U.K.-based BHR Group. Members include Infineum UK, NanoMaterials Ltd., Fuchs Petrolub, Petronas Lubricants and Multisol. Fiat and Ricardo are involved too, and the research lab InS. On the academic side are arrayed the brains of Stockholm University, Israels Weizmann Institute, Italys Politecnico di Torino and University of Salerno, and the Ecole Centrale de Lyon.

This team has been working to synthesize and characterize two promising materials, the inorganic fullerenes molybdenum disulfide and tungsten disulfide (IF MoS2 and IF WS2, respectively). As Dassenoy explained, the principal goal is to use these solid materials in engine oils, transmission fluids and greases to reduce friction and protect against wear. Infineum believes these materials could be the biggest breakthrough since the development of zinc dialkylthiophosphate some 70 years ago, and if the bottleneck can be opened, nano materials could significantly reduce friction and enhance durability, enabling further reductions in ZDDP in lubricants, he said.

Much of AddNanos efforts have gone into synthesizing nanoparticles and making them available in consistent, commercial quantities. This job fell to consortium partner Cidetec, which has developed an electrochemical synthesis process to make batches of IF MoS2. Initially able to make just 1 gram at a time, four years later this synthesis project was able to yield 1 kilogram per batch, Dassenoy reported. Consortium partner NanoMaterials, meanwhile, focused on making nano-scale tungsten disulfide, and now is also making 1 kilogram batches, he added. (NanoMaterials is a subsidiary of the U.S. firm ApNano, which makes a lubricant additive based on inorganic solid nanoparticles.)

With the Cidetec material in hand, it was time to create a dispersion of the nanoparticles into base oil. The next step was a large-scale blending process, for a total volume of 1,000 liters, said Dassenoy. We wanted to look at the stability of the dispersion over time. One good piece of news, he added, was that the effect of the addition of nanoparticles on the viscosity of the lubricant was found to be negligible.

Performance tests such as coefficient of friction also showed good results. But we also wanted to test the oil in an engine, to see if it had an effect on valvetrain wear, so we moved on to a full-scale engine wear test. During the first two cycles of the test, the nanolubricant performance was comparable to a reference oil, especially at low speeds. But as the test continued, later cycles showed greater benefits with the nanolubricant, especially as speeds and loads increased, Dassenoy said.

We also did roller chassis dynamometer tests to see the effects on fuel consumption and emissions abatement. Fuel economy was just okay, within Euro V standards, but a definite reduction in fuel consumption – maybe 2 or 3 percent – was measured in low-speed regimes.

From all this, it is clear that you can strongly reduce friction and wear when you introduce nanoparticles, but its not so clear why. More study is needed to control and optimize the tribological properties. This last step will be key, Dassenoy added. If you can optimize the dispersion and improve it, you may be able to reduce the amount of nanoparticles you need to add to the lubricant.

Also speaking at STLE was Ajay Malshe, founder and chief technology officer of NanoMech Inc. in Springdale, Ark. While automotive lubricants are certainly a glittering prize for nanoparticles, he observed that other applications have been faster off the mark. These early adopters have included industrial users who face severe boundary lubrication issues in hardworking equipment such as gearboxes, wind turbines and oilfield valves.

Rather than focus on a single particle, or a single lubricant property such as friction or extreme pressure, NanoMech has built a library of surface-active nanoparticles that it can assemble into nano-additive packets; the packets themselves may be larger than 100 nanometers, Malshe explained, and can deliver a variety of properties depending on the particles selected. Typically, one particle is not sufficient to do all we wanted, so we decided to develop a package, he said. Our goal was not to deliver one chemistry, but five or six chemistries at one time. Why just do load-carrying, we asked. Why not have multiple functions, such as extreme pressure, antiwear, anticorrosion, antifriction – maybe even fire retardance?

With that idea in mind, NanoMech has been working with the U.S. Department of Energy for about four years to develop a nanoengineered lubricant additive package, aimed at reducing the high rates of gearbox failure experienced in the wind energy industry. The gearbox is the most expensive component on the wind mill, with various gear types employed including planetary configurations with spur or helical gears, Malshe said. But its also one of the most short-lived, due to the difficulty of lubricating the rolling and sliding contacts, and gear tooth failures from micropitting. Fatigue, corrosive wear and fretting aggravate the damage.

Using an NLGI 2 grease treated with a NanoMech-developed nano-additive, researchers at Oak Ridge National Laboratory looked at how a nano-additive packet reduces surface wear. Microscope images of the metal surfaces showed the number and nature of micropitting wear clusters were all reduced, versus a reference grease. And the load-carrying capacity went from 250 kilograms to 620 kg, Malshe related.

Whats behind this improvement? When you have two surfaces in direct contact, with the asperities in contact, the question is how to produce all the lubrication needed right at that asperity contact point, Malshe later elaborated to LubesnGreases. Our hypothesis is that if you can increase the load-carrying capacity of the asperities, you could increase the wear performance.

One product from NanoMech already has reached commercial use and has been branded as Evermax grease by Cameron Inc., the worlds largest seller of oilfield valves. Cameron is using this grease in ball valves, blowout preventers and gate valves, and praised it in its 2013 annual report to shareholders. It reduces friction by orders of magnitude over traditional lubricants, the company said.

The next challenge is what Malshe calls an elephant on a tightrope – how to add a nanomaterial into traditional lubricant formulations without upsetting the careful balance of performance additives that it may already contain. Certain end users are already doing this themselves, he added. Of course, we work with customers to make sure our product matches the need. We dont just ship it to anyone and leave it to them to figure out. But yes, we can take an off-the-shelf, fully formulated gear oil, add our nanoadditive package, and see drop-in benefits. I know it sounds bombastic, but its working.

Greg Schwartz, NanoMech senior vice president, echoed that comment. We do not upset the balance of major chemistries. End users are pulling this, they were the early adopters. He said NanoMech is now manufacturing nano-additive packets in ton amounts, having scaled up from a pilot plant in northwest Arkansas. The commercial volumes are made at a custom chemical plant, using a proprietary process that Malshe declined to describe in detail, but said was conceived after he visited a chocolate manufacturing plant.

The packets themselves are manufactured in paste or gel form, or may be diluted in base oil if thats what a blender prefers. As for color, Schwartz said it can be whatever a blender or end user wants – creamy ivory, transparent green or something else. Treat rates are typically 0.5 to 2.0 percent in oil lubricants, and up to 5 percent in grease.

Another effort to synthesize nanoparticles is under way at the Lamcos Insa de Lyon in Villeurbanne, France, reported Pierre Rabaso in another STLE presentation. Here too, the focus is IF MoS2 and IF WS2. These are chemically inert, he pointed out, and have the advantage of being relatively easy and inexpensive to synthesize. However, there remains the issue of how to achieve optimal performance. One milliliter of fluid might contain 400 billion nanoparticles, Rabaso pointed out. Does it need to contain that many, or more, or fewer?

Nanoparticle size remains an issue as well, he added. Of course, a smaller particle will penetrate more easily at the contact point. Size also affects the concentration of particles you can achieve in the oil – smaller size means room for more particles.

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