"Broken nanodiamonds are forever," or so says a team of scientists at the US Department of Energy's (DOE) Argonne National Laboratory. By combining broken nanodiamonds with two-dimensional molybdenum disulfide layers, they've managed to produce a self-generating, very-low-friction dry lubricant with hundreds of applications that lasts practically forever.
Dry lubricants are an important tool for modern engineers, with a number of advantages over their liquid counterparts. Unlike greases and oils, dry lubricants aren't as chemically active, don't leak or squeeze out, and don't capture dust or grit. In addition, they don't break down at high temperatures and some work in the vacuum of space where liquids would evaporate or freeze solid.
One of the most common solid lubricants is graphite powder or paste, which is made up of plate-like carbon molecules with water molecules between them that act like extremely tiny ball bearings. It's used for lubricating locks, door knobs, and bicycle chains, as well as high temperature or high pressure environments. However, there are more exotic dry lubricants.
About three years ago, a team led by Anirudha Sumant of the Nanoscience and Technology division of Argonne found that by mixing graphene with nanodiamonds, it was possible for the first time on an engineering scale to produce superlubricity or near-zero friction. Now Sumant's team has taken this a step further by replacing the graphene with molybdenum disulfide – another common dry lubricant that's widely used in space industries because it performs well in a vacuum.
What they found was that when combined with molybdenum disulfide, the nanodiamonds spontaneously broke down and formed into balls of onion-like carbon. This was because the two-dimensional molybdenum disulfide molecules were disassociating into molybdenum and sulfur, which reacted with the nanodiamonds to form the layered balls by increasing the stress on their crystalline structure.
The result was a new dry lubricant that was 10 times slipperier than fluoropolymers like Teflon, that can sustain high contact pressure with very little wear, and tear and does not need to be applied in a thin film.
According to the team, the lubricant is also relatively inexpensive because, though molybdenum disulfide is more expensive than graphene, very little of it is needed for the proper effect to take place. Also, there are no hazardous chemicals involved and the lubricant is self-generating, so it effectively repairs itself during use.
The team sees the new, patented lubricant technology as having a wide range of applications, including bearings, pump seals, wind turbines, and magnetic disc drives.
"The material the lubricant is used on is going to last longer, and I don't have to worry about liquid residue and throwing out oily rags as part of the clean-up process," says John Harvey, business development executive at Argonne. "We also can use it to make parts that we can't make today, especially with metal stamping."
The research was published in Nature Communications.
The video below is a computer simulation of the nanodiamond lubricant.
Source: Argonne National Laboratory
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