The presence of laminate structures in certain carbon based compounds was known as early as the 19th century. The extraction of these structures in a cost effective manner has since remained a challenge. It wasn’t till 2004 that two scientists in the University of Manchester were able to isolate a single layer thick crystallite from bulk graphite. This two dimensional single layer of crystalline carbon became known as graphene.
Graphene can be shaped into different allotropes most notable of which is the nanotube.
Why Engineers should learn about Graphene?
Graphene was dubbed the best thing that happened in the world of material science when it was separated about 10 years ago. Its two dimensional structure and strong lattice gave it properties unlike any other material known to man.
Interestingly the discovery of graphene coincided with the end of Moor’s law era which stated that computing speeds (of computer processor) will double every 18 months. The reason why the increase in computational speeds has declined is because the operating limits of the materials that make up the processor have been reached. With the discovery of Graphene, Moor’s Law has reason to be upheld again.
Graphene has opened up new vistas in many areas of technology not just in electronics. If we are able to mass produce the material, bigger structures can be built, larger and more efficient vehicles can be developed and many chemical processes can be expedited.
In this article, 10 uses of Graphene in Engineering will be discussed. Some of these applications are already developed while others are undergoing research.
1. Stealth Technology
By combining the biomolecule “Reflectin” (a protein found in Hawaiian squids) and Graphene, scientists have developed a film that can change the way light is reflected. The change in reflectivity can be instigated by a chemical signal. Tests have shown that orange looking surface can blend into green foliage when the coating is activated.
Nanoflight an Israeli company already is claiming to have a coating that will make objects nearly impossible to detect. Work on stealth technology using Nano-materials is already underway in Germany, USA and India.
2. Water Filtration
Fresh water for human consumption is getting scarce. Furthermore, the availability of fresh water is compounded by the uneven distribution of resources. Although desalination process has been traditionally used where salt water is available but it is an energy intensive process. Using graphene as a filter can help in tackling this problem. Fortunately, work is being done in the academia (MIT) and the industry (Lockheed –Martin) for looking into the use of Graphene as a filter that would allow water molecules to pass through but block salt molecules.
“The key to achieving filtration is controlling the size of the gap in the graphene sheets” opines the MIT professor, Jeffrey Grossman.
The results have been promising and scientists are pleasantly surprised by the simulation studies. When this technology is realized, it could produce fresh drinking water from salt water for a fraction of the energy used in Reverse Osmosis / Desalination techniques.
3. Solar Cells
It is a well-known fact that energy up to 1100 Watt/m2 can be received through sunlight. Currently, not much of this sunlight can be converted into electricity. Even if the photons with the ideal bandgap are fully utilized, the conversion efficiency peaks at 33.7% known as Shockley –Queisser limit.
Although scientist have been able to bypass this limitation by using three layers of solar cell (Multi-junction) on top of each other, but the result has been a product that is economically viable for a domestic user. The other factor that lowers the conversion limit is the presence of charge carriers (mesh wires) that have to be placed on top of the solar cells. They prevent light to pass through them. Thus a portion of light is lost in absorption by copper or aluminium tabbing wires.
What makes graphene ideal for use in Solar cells is its electrical conductivity and optical transparency. Graphene material can be used as the charge carrying matrix that is placed on the top of solar cells. It has been reported that graphene based solar cells have already achieved an efficiency of 15.6% , which is very high for a flexible solar cell.
Graphene is already being commercially used in electronics industry. At the start of 2014, it was reported that the global market for graphene has reached $9 million dollars. The sales were mostly in the semiconductor and other electronic components.
Graphene because of its high conduction and transparency is ideal for optical-electronics and therefore can be used in touch screen applications. IBM was able to produce a working transistor with graphene in 2010. And it has been reported that this graphene transistor works twice at twice the speed of normal silicon based transistor.
The ideal properties of a lubricant are its environmental insensitivity, high durability, and ease of occupying space between rough interfaces. One of the biggest disadvantages of solid lubricants has been the wear and subsequent depreciation. Graphene due to its strength and atomically smooth structure is able to deal with shear forces much better than other solids. Secondly, graphene has been shown to be impermeable to liquids and gases, such as water or oxygen, thus slowing down the corrosive and oxidative processes that usually cause more damage to rubbing surfaces.
It has been shown to reduce wear not only in its use directly as a lubricant but also as an additive to oils, composite materials and solvents.
6. Structural Engineering
Graphene is the strongest material ever tested. It has a Young’s Modulus of 1 TPa and tensile strength of 130 GPa. This implies that extremely small amount of graphene material can take a load not several thousand but several million times its own weight. It is 200 times stronger than structural steel.
Unfortunately small scale of graphene is prohibiting its use in large structural components. However just like composites, that have made their way in aerospace and automotive sector, graphene based materials are poised to do the same. Graphene when used as a matrix with other materials can produce even lighter and more robust material than carbon fiber composites.
Research at MIT has shown that Graphene-polymer composites would be ideal for making lightweight gasoline tanks and plastic containers that keep food fresh for weeks.
One of the biggest problems that have plagued the battery technology is energy density. The arrival of lithium ion batteries to an extent has addressed the energy storage issue, but their use on a utility scale has still not taken off.
There is an inherent problem in the battery design. If more power needs to be drawn, the battery needs to have more charge carrying channels which reduces the space for charge storage. This is analogous to a passenger aircraft where increasing the number of aisles and doors would allow passengers to board/alight faster but on the other hand will reduce passenger carrying capacity of the aircraft.
As graphene is the most conductive material known to man, its use as a charge carrier will occupy less room compared to other materials. This will allow more space for charge storage in the battery. Thus with the use of Graphene, high power batteries can also be high energy batteries.
8. Thermal management
It has been ascertained that Graphene as a conductor of heat, outperforms all other conductors. Its conductivity under certain condition can reach 2500 Watt/m2K compared to copper which has conductivity of only 400 Watt/m2K. It can therefore be used as a heat spreader particularly in electronics. Processors tend to generate a lot of heat and their performance degrades with temperature. There are several devices that have been used to wick heat from the processors. The most common apparatus is blowers used with a heatsink. However, it is the transfer of heat from the processor to the heat sink that can prove to be the bottleneck. Graphene’s use as a thermal interface material can eliminate this bottleneck. Furthermore it has also been shown that Graphene filing inside a normal coolant improves the heat transfer capability of the coolant.
9. Contaminant removal
Graphene can remove many substances such as cobalt, copper, arsenate, cadmium and organic solvents from water and other liquids. Graphene oxide can successfully remove various contaminants by sweeping flocculation effect. Graphene based materials are being considered as sorbents for environmental decontamination. The most prominent use of which will be the removal of radioactive nuclides from sea water. It should be noted that one of the worst legacies of nuclear energy use is the contamination of both land and sea. Concerns were raised after the Fukushima disaster in 2010 on adverse environmental effects of nuclear leakage on western seaboard of USA which is over 3000 miles away.
When used as a sorbent, it helps in coagulating radio nuclides. An example of this was an experiment where simulated radioactive liquid was used and graphene oxide was introduced. Coagulation occurred almost instantaneously because of Graphene high sorption affinity for radio nuclides.
10. Sensory aid in prosthetic limbs
In prosthetic limbs due to the absence of nerve cells, the sensation of touch is lost. One of the possible solutions that scientist are looking into is using layers of graphene on the outer surface ( dubbed as e-skin or artificial skin). Normal pressure sensors operate on a range which is low pressure (<5K). At higher pressures the sensitivity of the normal pressure sensor is lost. Graphene based pressure sensors operate over a wide range of pressures. They can therefore be used for gentle touch as well as hard grab. Graphene based artificial skin is able to generate variation in electrical signals which are than transmitted to nerve cells. The test conducted on mice have already proven the functionality of graphene based artificial skin and extension to human trials is underway.
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