High-tech lubricant forms by itself when needed

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Lubricants that reduce friction are created precisely where friction is high: At TU Wien, this was achieved with special 2D materials. This is important for space technology.

Our bodies have a few things in common with machines: we have moving joints, friction and wear occur, so you need suitable lubricants. The body produces them naturally all by itself - something similar is now possible with machines.

By choosing suitable materials, it is possible to achieve that special 2D materials form under mechanical stress, which are highly effective in reducing friction - high friction thus leads to a reduction in friction all by itself, the system regulates itself. Especially for applications in space, where liquid lubricants fail and no maintenance is possible, this new technology holds great advantages.

Thin layers that slide over each other

Tribology, the science of friction and wear, has for years been intensively studying so-called 2D materials - particles consisting of only one or a few atomic layers. This class of materials includes, for example, molybdenum disulfide or molybdenum diselenide - in the center there is a layer of molybdenum atoms, with sulfur or selenium atoms coupled above and below.

-Such ultra-thin platelets can slide over each other with very little resistance-, says Philipp Grützmacher from the Institute of Engineering Design and Product Development at TU Vienna. -That’s why these materials are an excellent lubricant.-Philipp Grützmacher conducts research in the team of Carsten Gachot, who heads the Tribology Research Department at TU Vienna.

Unlike conventional lubricants such as Él, which are used in liquid form, 2D materials can be used in powder form. This is a great advantage especially when a machine is to function at high temperatures or in a vacuum, where liquids would evaporate rapidly. -This is why such lubricants play a particularly important role in space technology; they were used, for example, in the James Webb Space Telescope," says Carsten Gachot.

Under normal conditions on earth, however, such materials are difficult to handle. Contact with oxygen or atmospheric humidity can cause them to oxidize, rendering them unusable. -The ideal solution is a 2D material that is created exactly where it is needed," says Philipp Grützmacher. -And that is exactly what we have now developed.

Friction creates lubricant

You simply take a mechanical component made of steel and coat it with a layer of molybdenum a few micrometers thick. Selenium is then added in powder form. -When mechanical stress is applied, for example when two such components rub against each other, a tribochemical reaction occurs, selenium and molybdenum combine to form molybdenum diselenide flakes, which then act as a lubricant-, explains Grützmacher. -Our measurements show that as soon as strong friction occurs, the lubricant is produced, the friction immediately decreases drastically and continues to decrease over the course of the experiment.- Using special imaging techniques, it was possible to prove that this effect actually results from the formation of ultrathin molybdenum selenide layers.

Unlike coatings made of 2D materials synthesized in advance (e.g. MoS2), the starting materials (molybdenum and selenium powder) for the process do not decompose in contact with oxygen or atmospheric humidity. This significantly expands the range of applications for this lubricant system. This technology is not only interesting for space applications, but also for many areas of application in which liquid lubricants cause problems - for example, because high temperatures occur, because the process is to take place in a vacuum, or because contamination could occur when using Élen.

Another important advantage is that the lubricant is always formed exactly where it is needed, which can also be repeated at any time by simply adding powder. Thus, a significantly more efficient lubricant system with a longer service life has been created.

Original publication

P. Grützmacher et al, Se Nano-Powder Conversion into Lubricious 2D Selenide Layers by Tribochemical Reactions, Advanced Materials (2023).