In a recent joint paper by the Aerospace Technology Institute (ATI) and the National Graphene Institute (NGI) at the University of Manchester, researchers outlined the disruptive impact potential of graphene applications in aerospace.
The development of graphene dates back to 2004, when two University of Manchester scientists realized they had isolated a single layer of carbon atoms on a piece of scotch tape used to clean a graphite crystal. Since then, graphene has captured the imagination of researchers due to its fascinating properties. It is 200 times stronger than steel, very flexible, and is an excellent conductor of electricity.
According to the Manchester researchers, the two-dimensional material has the potential to positively impact aircraft performance, cost, and fuel efficiency. By incorporating atomically-thin graphene into existing materials used to build aircraft, the safety and performance properties of aircraft could be significantly improved. This in turn, could lead to reduced material weight and positive impact on the fuel efficiency of the aircraft and, as result, the environment.
In an exclusive introduction to the paper (published in ATI’s INSIGHT series), Sir Richard Branson said, “The potential for graphene to solve enduring challenges within the aerospace sector presents real opportunities for the material to become disruptive, and a key enabler in future aircraft technology. We need to accelerate the opportunity for the UK to realize the benefits from graphene by creating a portfolio of graphene-related research and technology projects which if undertaken would lead to real impact in our aerospace industry.”
Recent graphene development
This focus on graphene comes during a period of marked development of the material.
In February, Tohoku University and Nagoya University researchers discovered a way to form two new tri-layer graphene materials. Each of the novel material—both made of three layers of graphene—is layered differently and has unique electrical properties. The work has implications for the development of novel electronic devices, such as photovoltaic cells that convert light into electrical energy.
Graphene's carbon atoms are arranged into hexagons, forming a honeycomb-like lattice. The deliberate bi-layering graphene—either with the centers of the carbon hexagons layered immediately above one another, “AA-stacking,” or the displaced layering with a hexagon center above a carbon atom of the second layer “AB-stacking”—has been achieved successfully in the past. Furthermore, if an external electric field is applied, AB-stacking of two layers of graphene leads to the formation of a material with semiconducting properties.
However, the deliberate stacking three layers of graphene has proven difficult. The Japanese researchers developed a way to fabricate the two tri-layer graphene samples by heating silicon carbide using two distinct methods.
In one experiment, the silicon carbide was heated to 1,510°C under pressurized argon. In another, it was heated to 1,300°C in a high vacuum. Both materials were then sprayed with hydrogen gas in which the bonds were broken to form single hydrogen atoms, forming the tri-layer graphene.
The silicon carbide heated under pressurized argon formed into ABA-stacked graphene, with matching top and bottom hexagon layers sandwiching a displaced middle layer. The silicon carbide heated in a vacuum developed into ABC-stacked graphene, in which each layer was slightly displaced in front of the one below it.
When the researchers examined the physical properties of each material, they found that electrons behaved differently between the two types of graphene samples.
The ABA graphene was an excellent electrical conductor, similar to mono-layer grapheme. However, the ABC graphene, behaved more like AB graphene in that it had semi-conducting properties.
Just this month, a research team from the National University of Singapore developed a new graphene production method requiring 50 times less solvent than current methods, potentially opening the door for larger-scale, sustainable synthesis.
The conventional method for graphene production makes use of shearing forces to lift layers from graphite. These are then dispersed in large volumes of solvent (approximately one ton of organic solvent to one kilogram of graphene), which presents an issue of ecological sustainability. Often, when reducing solvent volume graphene layers reattach to the graphite.
The new method was discovered by exfoliating pre-treated graphite under higher than normal alkaline conditions, which triggers flocculation, prompting the graphene layers to cluster together into a slurry without the need to increase solvent content. The graphene slurry can then be separated into more commonly used monolayers.
The method prevents reattachment to the graphite via a newly introduced electrostatic process. The slurry can also be used directly to 3D-print conductive graphene aerogels, an ultra-lightweight sponge-like material.
The path forward
In a comment published concerning the INSIGHT paper, James Baker, CEO of Graphene@Manchester at the University of Manchester concluded, “Major generational improvements in the aerospace sector have been associated with embracing new materials. Aluminum and carbon fiber have seen planes become faster, greener, cheaper with more functionality. Now graphene and related two-dimensional materials can mark the next step-change.
“By incorporating graphene into the existing materials used to manufacture planes, performance properties could be improved across number of key areas. By utilizing the multi-functional properties of graphene and through collaboration between industry and academia, there are significant opportunities which can accelerate the next-generation of aerospace technologies.”
Furthermore, there is currently heavy cooperation regarding graphene development between Chinese researchers (China is a top producer of graphite) and UK researchers (at epicenter of graphene development). Both countries are in the midst of aerospace development, with the UK working to restore a waning industry full of aviation heritage and China becoming a burgeoning commercial hub and early adopter of new technologies.
How long before the aerospace industry sees the disruptive impact?Continue reading »