By: Dr. Akanksha Urade (Graphene & 2D Materials Science Writer)
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Graphene is increasingly being used as an additive to transform a growing number of products in practically every industry.
In this article, I will explore the use of graphene as a lubricant.
Graphene flakes have practically endless applications. It is added to other materials to improve strength, water resistance, flexibility and electrical conductivity. A tiny amount – typically, between 0.01%-0.5% – can produce dramatic improvements.
Graphene can be an inexpensive replacement for many incumbent materials.
The problem has been finding a reliable source for industrial volumes of the right quality graphene for specific applications.
Grandview Research predicts that the $130 billion lubricants business in will expand at a CAGR of 3.7% through , led by increasing global demand for higher-performance lubricants. Graphite is the primary incumbent material for lubricants. But graphite has a number of drawbacks – including that it only works in humid environments. Another disadvantage of graphite is the tendency of lamallae to rupture under severe mechanical loads, resulting in a limited lifetime and a higher coefficient of friction.
There are other problems with lubricants, including the use of ecologically hazardous additives or solid lubricants (such as molybdenum disulfide or boric acid). Both oil-based and solid lubricants do not bond well to the surfaces it lubricates and must be reapplied on a regular basis. Even under the best conditions, most lubricant oils eventually degrade over time due to oxidation.
Different forms of graphene have been extensively tested as a lubricant additive. Graphene’s use as a lubricant is attributed to a number of different physical-chemical properties. For example, graphene’s exceptional mechanical strength prevents material wear. Second, graphene has been demonstrated to be impermeable to liquids and gases like water and oxygen, slowing down the oxidative and corrosive processes that normally cause damage to rubbing surfaces. Furthermore, because graphene is an atomically smooth 2D material with low surface energy, it can replace the thin solid films that are typically used to reduce the adhesion and friction of various surfaces.
Graphene can also be utilized as an additive in lubricants to increase fuel economy and engine stability. Companies such as Graphenoil, Graphene-XT, HydroGraph, Versarien, NTherma and others have added different forms and quality of graphene to lubricating oil to enhance performance and stability, resulting in less wear and tear.
“The addition of graphene improves the oil’s tribological properties, making it more suitable for high-pressure, high-stress environments”, notes Simone Ligi, the Chief Executive Officer of Graphene-XT. “But the benefits of graphene do not stop there. Graphene has good heat transfer properties, essential to make lubricants safer at higher temperatures. All of these effects combined reduce engine noise and fuel consumption”.
People commonly associate lubricants with the fluids found in automobiles and industrial machines. While fluids make up the vast majority of modern lubricants, a subset of lubricants known as solid-state lubricants also exists. Argonne National Lab has been researching solid lubricants based on graphene as a cheaper, more efficient and longer-lasting alternative to oil.
Image Courtesy: Berman, Diana, et al. Science ().
The use of graphene and carbon nanodiamonds as a solid-state lubricant to better preserve ball bearings is a field of study that has progressed rapidly in recent years, from an intriguing idea to a nearly practical reality. When graphene flakes and nanodiamond particles brush against a large diamond-like carbon (DLC) surface, the graphene encapsulates the nanodiamond by wrapping itself around it. As nanodiamonds are spherical in shape, the graphene-nanodiamond combination may travel freely between the two surfaces while providing lubrication. In addition to their lubricating and corrosion-preventative properties, they have also demonstrated super lubricity effects in which friction is reduced to nearly zero.
“That’s a significant improvement over any other existing solid lubricants coating available today,” says Argonne’s Prof. Anirudha V. Sumant. “Also, the amount of graphene needed is very small and therefore cost is much lower and eliminating oil waste would be more environmentally friendly, which is a great side benefit.”
The same research team revealed graphene to be an excellent steel lubricant. A few atomic layers of graphene not only reduce the degree of friction in steel rubbing against steel by seven times and the amount of wear by 10,000 times, but can also significantly lower the risk of corrosion.
The advantage of graphene-based solid lubricant coatings over standard lubricants is their simplicity of application. It is applied by spraying a solution over a vast surface area and can coat virtually any shape or size.
In our earlier piece titled “Fake Graphene: Let the Buyer Beware,” I made it abundantly clear that high-quality, defect-free graphene enjoys superior properties to their oxidized counterparts, such as graphene oxide (GO). However, in their marketing and on the labels of their bottles, many companies that sell GO and reduced graphene oxide (rGO) call these materials graphene. Even with lubricant applications, this is still the case.
Image courtesy: Berman, Diana, Materials Today ()
When compared to the wear rate of graphene layers, the wear rate of GO is between one and two orders of magnitude higher. As can be seen in the figure, oxidized graphene has dramatically inferior coverage compared to high-quality graphene, and the presence of oxygen in GO may cause corrosion of steel, which, in turn, increases wear. Because of this, GO does not offer anything approaching the same level of wear protection as high-quality graphene.
Contemporary lubricants contain ecologically hazardous chemicals or are solid lubricants (such as molybdenum disulfide or boric acid). Both oil-based and solid lubricants degrade over time and must be replenished on a regular basis. Real, high-quality graphene, on the other hand, can persist for a long period because the flakes realign themselves during initial wear cycles. Graphene, which is entirely composed of carbon, is environmentally friendly. In specific applications, do I think that graphene lubricants could serve as a suitable alternative to the more traditional oils and fluids? Yes. Would graphene lubricants be a universal replacement for oils? No. There are a number of reasons for this, but the key factor is the lack of supply of high-quality graphene. Nevertheless, we cannot deny that graphene-based lubricants and oils are making their way onto the market. However, whether or not they will come to dominate the market depends upon the ability to manufacture industrial volumes of high-quality graphene.
References
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Berman, Diana, Ali Erdemir, and Anirudha V. Sumant. “Graphene: a new emerging lubricant.” Materials today 17.1 (): 31-42.
Berman, Diana, et al. “Macroscale superlubricity enabled by graphene nanoscroll formation.” Science 348. (): -.
Graphene is a material that consists of a single layer of carbon atoms arranged in a hexagonal lattice. Stacking layers of graphene on top of one another forms graphite, giving it a soft, slippery feel due to the layered structure.
Graphene is incredibly thin, flexible and strong, with exceptional electrical and thermal conductivity properties. Due to its unique properties, graphene has the potential to revolutionize various industries, including energy, electronics, transport, agriculture, wastewater treatment and health care.
This material has the potential to address certain global energy and pollution concerns. This quick guide examines some of the most common energy applications of graphene and how it plays a key role in meeting these energy demands.
Even though renewable energy sources are abundant and more environmentally friendly than the use of fossil fuel products, the occasional intermittency from solar panels and wind turbines requires a way to store and convert this energy to make it more efficient and cost-effective.
As a result, graphene has played a major role in the field of energy. It's considered one of the best solutions for clean and renewable energy on a large scale. Its high strength-to-weight ratio, low charging time and large surface area make it a great material for multiple energy technologies. Some uses of graphene include:
Graphene's unique properties are shaping a more efficient and sustainable future for energy production, storage and utilization, as seen through its various applications below.
Indium tin oxide (ITO) is used in solar cells because of its transparency, conductivity and thermal properties. Graphene has similar transparent and electrical properties, and the material's flexibility and 2D structure enable solar cells to be installed on any kind of surface.
Using electrodes made from graphene-based materials in solar cells improves the energy conversion more efficiently from solar energy into electrical energy. Graphene can also be used as a transparent conductive film in solar cells or to develop flexible and lightweight solar panels, which allow more light to reach the active layers.
Graphene-based batteries are one of the most developed energy storage devices that use graphene. The material allows lithium batteries to perform better, charge faster and last longer.
Producing heavy water to cool the reactors in nuclear power plants is costly and produces CO2 emissions. Graphene membranes provide a more affordable and greener solution to this process. In addition, graphene oxide particles dissolve easily in water and help absorb radioactive substances, forming lumps. These lumps can then be burned or recycled after removal.
This property means graphene can potentially be used to clean liquids for industrial use or replace metals in catalysis, especially in raw material extractions. Bringing metals up to the surface involves large amounts of water that contain natural radionuclides. Graphene oxide can clean this water and improve the area's environment.
Thermoelectric generators generate electricity from thermal energy through the thermoelectric effect. The semiconducting materials create a difference in temperature between the elements, which causes the flow of electrons, generating an electrical current. The higher the difference, the higher the efficiency of the thermoelectric generator.
Graphene can be used in thermoelectric generators to improve energy conversion efficiency by enhancing heat transfer and electrical conductivity. Carbon-based materials, such as graphene, contribute to environmentally friendly solutions compared to materials that may contain toxic elements. Graphene's larger surface area, flexibility and light weight provide different sites for interaction with other materials in portable and adaptable composite films.
Distillation is an energy-intensive process due to its temperature and vacuum requirements. Heat is needed to boil fluids to create vapor that can be condensed and collected. Additionally, some forms of distillation require a high vacuum to lower boiling points and allow the separation of components at lower temperatures. Due to the equipment and design of distillation equipment, large-scale production can be challenging.
A graphene membrane's physical properties can help distill ethanol at room temperature without needing a vacuum like in conventional distillation methods. This capability means it could potentially be used in alcohol distillation and fuel and water purification.
Another attribute of graphene's physical properties is that it can block small molecules like helium from passing through its membrane. This process drops fuel crossover and improves the conductivity and efficiency of fuel cells, which are emerging as energy-converting devices with low to no environmental effects. Graphene acts as a catalyst and lowers fuel crossover instances, thereby leading to more reliable and sustainable energy generation.
With graphene containing multiple extraordinary properties, its use in materials and energy-based technologies will continue to rise. It can significantly improve technical issues and optimize other materials and processes for better yields. Ongoing research and product development will continue to find more benefits of graphene in the energy industry and other innovative solutions.
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