Graphene Is A Carbon Material That Is 1-Atom Thick, Learn How It Can Be Used For Space Propulsion Systems, And Other Facts.

Image Credit:- wikimedia

Introduction

So you decided to take a look at what Graphene is all about, the super-strong, highly conductive, magnetic material is also being considered to have uses in space craft propulsion.

Well in 2010 the Nobel Prize in Physics was awarded to two scientists for their work in producing and characterising properties of Graphene; the difficulty was to isolate large enough sheets to study. These two scientists are called Andre K.Geim and Konstantin S.Novoselov at University of Manchester UK.

Image Credit:- wikimedia

Different forms of Carbon:
(a) Diamond, (b) Graphite, (c) Lonsdaleite, (d) C60 (Buckminsterfullerene), (e) C540, (f) C70, (g) Amorphous carbon, (h) single-walled carbon nanotube

Graphene is a form of Carbon, we are all familiar with this element, it's what all life forms on Earth are created from. Carbon can take the form of Diamond when under great heat and pressure, the most abundant form of carbon is Graphite which we use in our pencils due to it's very soft nature, with Graphene like layers. You probably would have formed Graphene at some point when writing without even knowing it. Graphene is an unusual form of Carbon due to it's recently studied physical characteristics and properties.

Research in Graphene is proving to be very valuable indeed, scientists have added gold atoms to Graphene layers and achieved high electrical conductivity. Space agencies are now putting funding into projects to investigate the uses of Graphene in space craft propulsion because it emits electrons when a photon hits it, and this basically gives a small force. They is a growing use of this material which is proving to be quite special with it's applications, some of the potential uses include:

• Solar Cells
• LEDs
• Interactive Touch Panels
• Super-capacitors
• Drug Delivery
• Opto-electronics

This was just to name a few of the applications. So now we'll find out a bit more of the physical characteristics of this material.

You can actually create your own Graphene at home, this technique was suggested R.Rouff and his group, they weren't able to identify single layers, However the Nobel winning scientists managed to produce it with this simple technique. Take a pencil, scribble on the paper so you have a visible quantity of graphite, then find some sellotape and put it on the graphite and peel off the tape. You will then have produced some Graphene structures, of course it will consists of sheets, but if you repeat a process of using sellotape on the sellotape and peeling it, you keep reducing the number of layers until eventually you may produce a single sheet. So if you want you can make your own super material, but I don't think you'll have the equipment to analyse it sorry, unless anyone has a big juicy steemit wallet haha.

Graphene Properties

Image Credit:- wikimedia

Graphene, showing it's single layer hexagonal structure, all the balls are Carbon-atoms and the lines that join them are their electronic bond.

Graphene is a single sheet/layer of carbon atoms arranged in a hexagonal structure, like honeycombs, you can see an example of this in the image above. The average distance between each atom is about 0.14 nano-meters, and the thickness is about 0.4 nano meters, so it's a bit thicker than the space between the atoms, but it's very close. Due to it's electronic structure and 2-D nature it behaves differently to typical 3-D materials.

There is something called a fermi surface that all materials have and it relates the electric conductivity of the material, Graphene has an unusual Fermi surface and this gives it the unusual electrical behaviour. An electronically neutral sheet of Graphene in fact has low conductance, so does not transmit electrical energy well, but when you add or remove and electron to the material this drastically changes the Fermi surface and the conductivity. The action of adding or removing and electron is called doping, and when Graphene is doped the conductivity has the potential to be higher than copper at room temperature.

Image Credit:-wikimedia

Fermi Surface of bulk Silver, this is not the shape of the silver. It is instead the shape associated with where the energy is equal to the Fermi Energry.

There are some slight limitations due to the nature of it's structure. It has quite poor structural stability, it's difficult to reproduce the exact same samples. The addition of Gold-atoms to it's structure seems to be a solution to these problems, not only does it increase stability, but it improves electrical conductivity and biocompatability. This material could be interesting to biologists as it seems to be a good substrate to conduct bio-imaging techniques, which could be helpful in stem-cell differentiation studies.

Graphene has taken the top spot of being the strongest material known to man, it's 200 times stronger than steel, and stronger than it's brother the Diamond. Be sure to understand this point, when I refer to strength I am taking about about the bonds between the Carbon-atoms, these covalent carbon-carbon bonds are the strongest we know, and it's this that makes the Graphene world's strongest material. Of course if you made Graphene as I described, you could easily cut or tear the sellotape with the Graphene on it, it's only one-atom thick, so you just need to use enough energy to break the covalent C-C bond, don't imagine it's harder than a block of steel. If we succeed in making large scale Graphene-like materials, then we could see something quite indestructible to an extent.

The thermal conductivity of Graphene is also something of interest, it's exceptionally high compared to other materials. Reported values of of conductivity are 1500-2500 Watts/meter/kelvin, the large range of the values is due to the difficulty in producing pure sources of Graphene, any impurities in the structure will effect it's conductive performance. The reason it is able to thermally conduct so well is because the bonds between the carbon atoms are easily vibrated and can vibrate a lot without breaking the bond, the vibrations will store and transfer energy; these vibrations are called phonons. However, when a Graphene sheet is put on a substrate (another material, like a glass slide) this significantly changes it's conductivity as the vibrations are absorbed by the substrate. Due the configuration and strong bonds between atoms the Graphene has been calculated to be over 5000 degrees Kelvin, which is very high compared to titanium that melts at 1668 degrees. This property allows the Graphene to act as a very good heat sink and absorb and distribute heat effectively.

Graphene has interesting magnetic properties too, it has strong diamagnetism which causes it to repel from a magnetic field; due to magnetic inductance. This diamagnetism is also non-linear which means it's effects are different depending on the orientation of the lattice to the external magnetic field. It's been observed that Graphene can be levitated by neodymium magnets, as you can see an example of in the picture below.

Image credit:-wikimedia

Example of magnetic levitation of a pyrolytic carbon, this is the same effect that has been observed with Graphene.

The study of Graphene has been rapidly growing over recent years, and scientists are still finding unusual properties when studying effects of Graphene and Graphene-like materials. The structure with it's hexagonal lattice is what lends to exotic behaviour, and the strong lattice bonds give rise to high conductive behaviour; both thermal and electrical. In the next section we'll look at how light can cause electrons to be ejected form the surface of Graphene, which is looking like a strong candidate for high-precision space craft control.

Graphene As A Propulsion Method

Image Credit:-nasa.gov

This is an Illustration of Ion propulsion, another form of propulsion system but has similarities.

As you may have gathered from the information in this article so far, Graphene in it's pure form is strong yet fragile to macroscopic forces, like cutting the Graphene on sellotape with scissors. We can try to build larger scale Graphene-like structures with Graphene sheets but the interaction of layers effects and reduces the properties that have been described like conductivity. However when care is taken to construct a large scale sample of bulk Graphene, the depletion of the intrinsic properties is minimal; you can full information in the references. The sample I will refer to is "centimeter sized and milligram in weight", so it's a considerable size compared to the nano meter structure, and has a spongy like feel to it. A physical process occurs on this material when you shine light on it, it's called light-induced ejected electron emission. Basically when you a particle of light (photon) strikes the surface the interaction causes an electron to be emitted from the surface. Due to Newton's 3rd Law, these is a force experienced on the Graphene as a result of this ejected electron. However, this force is much greater than pressure caused by light-radiation (light carries momentum and has a force associated to it), the radiation pressure is strong enough to propel the material but the electron ejection pressure is a lot stronger. One the scale of a single interaction this force is not much, but lasers are high intensity so can deliver a lot of photons resulting in greater propulsion forces.

Image Credit:- phys.org

The force generated by this mechanism is not stronger than the force produced by combustion of rocket fuel, it would be used as a primary propulsion method. Instead it's use would be more directed to a final propulsion method, it could be used for slight movements when docking another craft for example. The propulsion system would use a high powered laser and illuminate the Graphene causing electron ejection. The force of the electron ejection is proportional to the energy of the photon that caused the interaction. If we use a laser source that has a very small range of frequencies, we can accurately know the force of the electron. The power of the laser depends on the number of photons emitted per second. So if we accurately know the power of the laser, the number of photons per second, the energy of the photons, then we know exactly how much force is being applied to Graphene. With high-tech instruments, especially when we talk about space agencies, we would able to control this mechanism very finely.

This is something that space agencies are looking into heavily at the moment. I am making a Phd proposal to work with this Graphene looking at the propulsion characteristics, but I want to propose something that could be quite unique. But I can't tell you.....Yet :D

Conclusion

Graphene is a fascinating material, it could lead to many advances in different areas of scientific research. It's conductive properties make it a very promising for electronic devices, thermal properties allow it to absorb heat fast and can make fantastic heat sinks. It's extremely strong but still fragile and has abnormal magnetic properties. Bulk Graphene shows very promising signs of being a good method of precise propulsion systems, and space agencies are digging deeper; well going higher. I hope you learnt some interesting facts of Graphene in this article, I would love to hear opinions and read some comments, let me know what you think, and don't forget to follow for future posts. Until next time.....

@physics.benjamin

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References:-

• Graphene in zero G promises success in space - phys.org
• Graphene - Nobel Prize
• Potential applications of graphene - wikipedia
• The Graphene–Gold Interface and Its Implications for Nanoelectronics
• Graphene–Gold Nanoparticles Hybrid—Synthesis, Functionalization, and Application in a Electrochemical and Surface-Enhanced Raman Scattering Biosensor
• Macroscopic and Direct Light Propulsion of Bulk Graphene Material

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