Tribochemistry Begets Sustainability?


Tribochemistry Begets Sustainability?
© sompong_tom

“Tribochemistry is the study of reactions that occur between lubricants and surfaces they are exposed to under severe operating conditions known as boundary lubrication,” Neil Canter, a fellow with the Society of Tribologists and Lubrication Engineers, said in a podcast episode sponsored by the organization.

While it may seem obvious why tribochemistry is a key science in the lubricants industry, what may be less clear is how tribochemistry can enable the use of lubricants in a more sustainable manner.

Primarily, tribochemistry can be used to find innovative ways to reduce friction and increase energy efficiency while also cutting costs. In the same podcast, Kuldeep Mistry, product development specialist with the Timken Company, explained that within a passenger car, a significant amount of energy is lost during operation. “There’s a lot of tribochemistry going on” in the engine and transmission, he said. “There are a lot of tribological components. They are kind of rubbing against each other and what is being found out is we are losing millions of euros because of this. So if you manage a good tribochemistry here, if you have the right lubricant for the right materials, you will be making significant savings because the efficiencies will increase and the components will last much longer.” 

The same applies to other types of equipment, like that used in aerospace and mining applications. “There are so many components, like gears or bearings, and they all are being lubricated and they all have lots of tribochemical interactions going on,” Mistry said. “Hence, it is very, very important to consider some of these aspects.” 

Gains in efficiency will result in lower emissions, too. “We are making tremendous progress because of better understanding of the tribology, of the tribochemistry,” Mistry said. “We are getting better understanding and we are getting the really low-friction options. We are getting lower wear-related failures now, and this is all really helping us out big time.”

Tribochemistry can also offer insight into how lubricants will perform when paired with different types of metals and coatings used in engines and other components. “Using the knowledge gained by tribochemistry, we are trying to understand the right combination of the lubricant and the metallurgy—and which can give you the lowest friction and lower wear,” Mistry said. “But also at the same time, we are trying to get a higher power density. So people are going for the lighter weight [materials], and they’re looking into different alloying options. This is all going to help out in the longer term because it would be making the systems more efficient. It is going to make it more durable. They will last much longer.”

Nicolas Argibay, staff scientist in the Materials Science Center at the U.S. Department of Energy’s Sandia National Laboratories, said in the same podcast episode that tribochemistry can offer different, greener solutions to the lubricant industry’s most pressing sustainability problems. As an illustration he offered an article published by The New York Times on July 18, 2016, titled “Grinding Chemicals Together in an Effort to Be Greener.” The article describes a competition between University of Cincinnati Professor James Mack and his middle school-aged son in which they raced to prepare a batch of stilbene. To do so, Mack set up a traditional wet chemistry station, which included heated flasks and stirrers. His son used similar ingredients but instead used a ball mill to activate the necessary reaction. 

“You can imagine who won the race, not only achieving a substantially faster outcome, but also significantly higher yields,” Argibay said. “And all this at a safer room temperature.” The margin of victory for the son was about two hours.

What does this anecdote have to do with tribochemistry’s ability to facilitate a more sustainable future? By highlighting a safer, simpler alternative to standard practices in the chemistry field, it goes to reason that advances in chemistry can lead to gains in other areas. “I think it’s safe to say that a green chemistry movement is underway that will be intimately tied to tribology methods and research goals,” Argibay said. 

Furthermore, Argibay explained: “Tribologists and our community can engage with a broader community of scientists and industry partners on the development of tribochemical processes to address climate change and secure a more sustainable future. That is, we need to look beyond wear and friction reduction—which is dear to our hearts and not going anywhere—but start to look toward impact potential and chemical processing. Specifically, there’s what appears to be extraordinary unrealized potential in the development of tribology-enabled alternative routes for traditional chemical synthesis routes.”

Argibay took note of an article written by Karen Ardilla Fiero and Jose Hernandez titled “Sustainability Assessment of Mechanochemistry by Using the Twelve Principles of Green Chemistry.” The article provided several examples of how ball milling, grinding and twin screw extrusion can be used as more energy efficient, safer and lower waste alternatives for the synthesis of host chemicals and materials, such as metal-organic framework. MOF is “a promising material system for efficient storage of hydrogen, and numerous organic and inorganic compounds, like those needed for manufacturing of permanent magnets, for example,” Argibay said. Permanent magnets are used in electric vehicle motors.

Tribochemistry in Practice

How is tribochemistry employed today to increase sustainability in the lubricants industry? 

“An exciting example of a tribochemical process from our group at Sandia was with the somewhat recent discovery of an in-situ room-temperature formation route for what are highly-wear resistant and lubricious diamond-like carbon, or DLC, films,” Argibay said. “This could, in some cases, obviate the need for synthesis chambers and expensive processes altogether, and even enable the possibility of exciting new prospects, like designing self-healing or ‘anti-fragile’ systems. For example, these methods could be used to reduce and, in some special cases, possibly even remove or obviate the need for oil lubrication in mechanical devices like gear boxes and bearings. So imagine the possibility of in-situ diamond-like carbon formation in bearings as an alternative to traditional oil-delivered lubrication. I should point out an important caveat: This is only, of course, something you can do in applications for which cooling rate is not the limiting factor.”

That is to say that Argibay and his team “showed that it is possible to generate full-coverage films of diamond-like carbon in a shearing contact on the surface of an extremely hard and ultra-wear resistant platinum-based coating, which was deposited on cheap bulk material, like steel,” he said. 

Furthermore, Argibay’s team managed to do so without significantly increasing material costs. “You hear platinum, and you think expensive,” Argibay said. “Yes, you know platinum is expensive, but when you’re putting a coating on the order of 100 nanometers in thickness, this incurs negligible additional material costs compared to, say, the sort of traditional deposition of diamond-like carbon coatings and so on. The tribochemically grown thin films had all the characteristics and properties of engineered diamond-like carbon coatings—including super-lubricity—and were generated by the decomposition of ambient hydrocarbons, like alcohol vapors at room temperature, which was another helpful feature.”

It may still be a bit too early to establish a clear view of tribochemistry’s value proposition. “The complexity of reaction processes and demands for higher fidelity and in-situ characterization to better understand and optimize these tribochemical processes present substantial but highly compelling academic challenges,” Argibay said. “Additionally, many applications where there could be opportunities for improving properties, like wear life, carry a high risk and cost of entry in the implementation of new technologies that would radically shift the traditional approach and established method of doing things.” 

However, there is mounting evidence that the benefits will outweigh the costs, he said. “Finding low barrier to entry or early adoption opportunities will be a critical step toward what are sure to be far-reaching improvements in efficiency, safety and sustainability.” 

Argibay cited an example of an application in which the risk and cost of entry are relatively low but the impact potential is significant: the development of new additives for oil lubrication for devices, like gear boxes and piston engines, as well as the development of combined lubricants and coolants that could be optimized for EV powertrains. “A central idea in these low costs or beachhead markets is that changing additive formulations, for example, would not likely require significant changes to designs or basic materials already in use” in engine blocks and other widely used components, he said. 

“Finding low barrier to entry or early adoption opportunities will be a critical step toward what are sure to be far-reaching improvements in efficiency, safety and sustainability.”

– Nicolas Argibay, Sandia National Laboratories

There may be concern that using traditionally cost prohibitive materials, like platinum, could result in high costs. “The idea seems it probably is still too radical for industry adoption, but continued development may lead to the discovery of cheaper, alternative materials and routes that can overcome what is, in some part, an emotionally rather than financially motivated response,” Argibay said. “It’s not surprising that a designer would suppose that noble metals are too expensive to introduce a new gearbox or bearing.” However, coating a surface area of one square meter with a 100-nanometer film of pure platinum would cost only $74 in materials costs, he said.

“There are real costs to taking the risks of redesigning something that works well and has been fine-tuned and optimized,” Argibay said. “So this again speaks to this idea that some beachheader entry points for tribochemical processes may be lower cost or lower risk than others, and we certainly want to pursue those first. But I think as we gradually show that we can do these things and do them well, the benefits become clear and we’ll see that radical changes can be very beneficial from a cost standpoint, a sustainability standpoint and so on.”  

Sydney Moore is managing editor of Lubes’n’Greases magazine. Contact her at

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