Mar 12 2021
As the Mars Perseverance Rover of NASA continues to investigate the surface of the planet Mars, researchers on Earth have designed a novel nanoscale metal carbide that could serve as a 'superlubricant' to decrease wear and tear on upcoming extraterrestrial rovers.
Photo illustration of a Mars rover designed by Missouri S&T students depicting the idea of MXene superlubric sheets applied to the machine’s moving parts to reduce friction and wear. Image Credit: Shuohan Huang/Missouri University of Science and Technology.
Scientists from the chemistry department at the Missouri University of Science and Technology (Missouri S&T) and the Center for Nanoscale Materials at the Argonne National Laboratory, exploring a group of 2D nanomaterials called MXenes, have found that the new materials work well to decrease friction.
According to Dr Vadym Mochalin, an associate professor of chemistry from Missouri S&T who also headed the study, the new materials should also perform better than traditional oil-based lubricants in adverse surroundings.
These superlubric materials are of special interest for advanced anti-wear and lubrication applications in extreme conditions, like those now experienced by the Perseverance rover on Mars.
Dr Vadym Mochalin, Study Lead and Associate Professor of Chemistry, Missouri University of Science and Technology
Dr Mochalin and his collaborators have described their findings in an article published in the March 2021 edition of the Materials Today Advances journal, titled “Achieving superlubricity with 2D transition metal carbides (MXenes) and MXene/graphene coatings.”
The Mars Connection
Mochalin informed that he could relate between this study and the journey of the Perseverance rover to Mars after watching the landing of the rover.
When I watched the landing of the rover on Mars, I thought: ‘What if the lubricant in one of its wheels fails? Then I made the connection with our work on MXenes, because it came to mind that we have just found that MXenes demonstrate superlubricity in an atmosphere devoid of oxygen and humidity, close to what is there on Mars.
Dr Vadym Mochalin, Study Lead and Associate Professor of Chemistry, Missouri University of Science and Technology
MXenes (pronounced as Maxines) are essentially metal carbide materials that have exotic properties. For instance, these materials can conduct electricity, which makes them suitable candidates for use in optoelectronics, sensing and energy storage applications. In this recent analysis of the materials, Mochalin and his research team performed a range of tests to find out how well these MXenes act as solid-state lubricants with specific materials.
Friction Testing
The team performed nano-scale ball-on-disk friction tests by adding a titanium carbide MXene onto a silicon substrate, or the disk, coated with a thin silica layer, which is the crucial component of sand.
They subsequently tested the ability of MXene to tolerate wear by allowing it to slide against a carbon-coated, diamond-like steel ball. These tests were performed in a dry nitrogen condition, which considerably decreases humidity.
According to Dr Mochalin, these tests demonstrated that the MXene interface between the silica-coated disk and the steel ball caused a friction coefficient in the 'superlubric regime' of 0.0067 to 0.0017.
The term friction coefficient denotes the amount of friction that exists between a couple of objects and it is established by a value that is typically between 0 and 1. If the value is lower, the friction will also be less.
When the researchers introduced graphene to the titanium carbide MXene, they observed even better results. The addition of graphene “further reduced the friction by 37.3% and wear by the factor of 2” without impacting the superlubricant properties of MXene, wrote the investigators in their article.
“These results open up new possibilities for exploring the family of MXenes in various tribological applications,” wrote Dr Mochalin and his collaborators. Tribology is the study of wear, friction, and lubrication of interacting surfaces.
Down-to-Earth Benefits
Although these superlubricants may prove handy for machines used in extraterrestrial surroundings—from asteroid mining equipment to Mars rovers—they are likely to have more down-to-earth advantages. MXenes are different from oil-based lubricants and would not depend on non-renewable energy sources, like petroleum or coal, added Dr Mochalin.
Shuohan Huang, a PhD candidate in chemistry from Missouri S&T, is the lead author of the study and closely works with Dr Mochalin on the analysis of MXenes.
Dr Mochalin’s Missouri S&T team investigates the underlying chemistry and physics of the materials and designs their properties and promising applications in sensing, mechanics, energy storage, and optoelectronics.
Huang and Dr Mochalin’s co-authors on the study are K.C. Mutyala and A.V. Sumant from the Center for Nanoscale Materials at the Argonne National Laboratory.
Journal Reference:
Huang, S., et al. (2021) Achieving superlubricity with 2D transition metal carbides (MXenes) and MXene/graphene coatings. Materials Today Advances. doi.org/10.1016/j.mtadv.2021.100133.