Physics trivia

Graphene

Graphene is a material produced from graphite. Its incredible physical properties make it a material with many technological applications.

Despite having the height of an atom, the graphene layer is visible to the naked eye due to relativistic effects that arise in its structure.
What is graphene?

Graphene is the thinnest material in the world. It consists of a two- dimensional layer of carbon atoms arranged in hexagonal structures, whose height is equivalent to that of an atom. This material can be produced by extracting surface layers of graphite, an abundant mineral on Earth and one of the most common allotropes of carbon .

The chemical bonds formed between the carbon atoms and the thickness of graphene make this element record -breaking in some physical properties , such as mechanical strength , thermal and electrical conductivities . These characteristics make graphene one of the most promising materials, which can be used in the most varied applications.

Graphene is a two-dimensional crystalline allotrope of carbon and has incredible physical properties.

What makes graphene special?

Graphene has incredible physical properties that make it a material with many technological applications. Learn about some properties that make this allotrope so special.

mechanical properties

Graphene is the strongest material ever known, being able to withstand pressures of up to 130 gigapascal (130.10 9 Pa). Such resistance stems from the strong chemical bonds formed between its carbon atoms. Materials widely used in civil construction, such as steel , withstand only one third of this pressure.

Another interesting property of graphene is its high Young ‘s modulus , indicating that, in addition to being resistant, this material is quite elastic and, therefore, returns to its original size with relative ease.

The small areas of each carbon hexagon are responsible for graphene’s high impermeability, which can be used as a small net capable of holding gases that leak very easily from their containers, such as hydrogen gas . In addition to being extremely resistant, graphene is very light : its density is 0.77 g/m² , about a thousand times lighter than a sheet of paper.

electrical properties

Electrons can propagate in graphene almost freely without suffering deflections or collisions. Due to the hexagonal structure of carbon bonds, electrons move within these thin layers at relativistic speeds, close to the speed of light .

At room temperature, the electrical resistivity of graphene is the lowest we know of, about 10 -6 Ω.m , lower than the resistivity of silver , the best known metallic conductor .

optical properties

Despite being a layer of carbons with a height of a single atom, graphene is visible to the naked eye, as it allows the passage of 97% to 98% of the incident light. This optical behavior arises from the relativistic properties of electrons in graphene. This implies that, by stacking several sheets of graphene, it is possible to produce a perfectly black body , capable of absorbing almost all the radiation incident on it.

thermal properties

By virtue of its electronic properties, graphene is an excellent thermal conductor . This material is able to dissipate heat faster than any other known material. In addition, some studies suggest that its melting temperature is 4125 K, about 3851 ° C .

Stable, two-dimensional graphene was accidentally discovered in 2004 by Russian physicists André Geim and Konstantin Novoselov . This discovery guaranteed the researchers, in 2010, the Nobel Prize in Physics. The existence of this carbon allotrope, however, had been known since the 1930s.

What is the price of graphene?

The price of graphene is still high due to its complex means of obtaining it. The most current techniques that allow the production of pure and thin layers of this material work with the deposition of vapor on metallic substrates, such as copper sheets.

Currently, a 5.08 cm by 2.54 cm sheet of graphene , about 12.9 cm², can cost as much as $ 275 : an average of 21 per square centimeter However, factors such as impurities and asymmetries can drastically reduce this price.

Another way of obtaining graphene is from graphite: with 1 kg of graphite, which costs around 1 dollar, it is possible to produce up to 150 g of graphene, whose value exceeds 15 thousand dollars ¹.

Where do we find graphene?

Despite being an allotrope of carbon, like graphite and diamond, graphene is not found in nature in its two- dimensional configuration , that is, containing only one atom in height.

In the two-dimensional form, graphene has its chemical stability drastically reduced, despite acquiring physical and chemical properties that make it an excellent conductor of heat and electric current and the most resistant material ever known. Thus, in nature, the occurrence of multilayer graphene is privileged, which is much less interesting for technological applications.

What is the composition of graphene?

Graphene is composed of carbon atoms linked in hexagonal crystal structures through sp2 bonds. These bonds repeat along a two-dimensional plane, only one atom high.

What can you do with graphene?

Graphene is one of the most promising materials known. Its technological applications are vast and limited to the production capacity of this material on large scales. Devices such as folding LED screens, photovoltaic cells (solar panels), stronger touchscreens, more efficient transistors , supercapacitors , heat sinks and cell phone superbatteries are some examples of technologies possible through the application of graphene. Recently, a student at the State of California University showed that, by subjecting a graphene disk to an electrical charge for two seconds, it is possible to keep an LED lit for up to 5 minutes.

graphene in Brazil

Brazil is in the technological race in search of obtaining cheaper and more efficient methods for the production of graphene. According to a report produced in 2012 by the National Department of Mineral Production (DNPM), in a few years, the graphene market should be one of the most profitable in the world, with the potential to reach up to 1 trillion dollars in 10 years. In addition, Brazil has the largest graphene reserves in the world .

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