Researchers at Argonne National Laboratory combined nanodiamonds with layers of molybdenum disulfide layers to create a very-low-friction dry lubricant that lasts so long it could almost be confused with forever, according to Argonne. The substance could have hundreds of industrial applications and can be used virtually wherever two pieces of metal rub together in dry conditions.
The most commonly used solid lubricants on the market today take the form of graphite paste. They are used as lubricants to grease doorknobs and bike chains, among other things.
In 2015, one of the researchers, Anirudha Sumant, made a breakthrough in solid-lubrication technology by demonstrating superlubricity (near-zero friction) at engineering scale for the first time by using graphene combined with nanodiamonds. This approach was revolutionary, and since then his group has continued to further develop the technology.
Most recently, Sumant replaced graphene in the process with molybdenum disulfide to see how other materials would behave. He was expecting the process to resemble the one observed with graphene-nanodiamond lubricant. However, the team was surprised when they couldn’t see nanodiamonds in the material. Instead, they found balls of onion-like carbon.
The molybdenum disulfide was breaking up into molybdenum and sulfur and reacting with the nanodiamonds to convert them into onion-like carbon. Onion-like carbon consists of several layers of spherical graphitic shells that can be used as a dry lubricant. And the process of combining molybdenum disulfide and nanodiamonds automatically creates this form of carbon without any additional chemical application. The lubricant is also self-generating and readjusts itself continuously, so it lasts longer.
These carbon balls sustain high contact pressure and, due to their unique nanostructure, glide easily, creating superlubricity. The team concluded that the sulfur diffusion increased the strain in the nanodiamonds, subsequently breaking them and converting them into onion-like carbon.
The friction in this new combination is one-tenth that of some nonstick coatings including fluoropolymers, which means less heat and less wear and tear on parts and equipment. It also means the machinery and parts the lubricant is used on will last longer, and there won’t be any hazardous liquid residue or the need to use and dispose of rags as part of the clean-up process. It can also be used to make parts that can’t be made today, especially with metal stamping.
Although molybdenum disulfide is a bit more expensive than graphene, less is needed in this process. “The amount is so small, a few drops for kilometers of sliding, that cost is not an issue,” says Sumant.
The potential applications include bearings and mechanical pump seals in dry applications as well as in wind turbines. The technology could also be used in the computer industry for magnetic disc drives.
Argonne already has three patents on the superlubricity technology, with a patent pending on this breakthrough, which will soon be available for licensing.
