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  • In 1991 a Japanese physicist, Sumio Iijima, conducted a momentous experiment.

  • An experiment that introduced the world to material so strong that it could revolutionise

  • how engineers approach design.

  • Taking two graphite rods as electrodes, Sumio applied a current across the rods.

  • A spark arched between them and with it a cloud of carbon gas puffed into existence,

  • vaporising the tip of the anode rod.

  • As the carbon laden air settled on the chamber walls it formed a thin layer of black soot,

  • within it a strange new material appeared.

  • Tiny single layer straws of carbon.

  • Sumio Iijima had just created carbon nanotubes.

  • [1]

  • Laboratory testing of these mysterious little tubes in the following years would reveal

  • that these nanometer-wide hexagonal lattices of carbon had the strongest tensile strength

  • known to man, and this was just As one of the many incredible material properties they

  • displayed.

  • Carbon nanotubes are light, conductive and biocompatible.

  • [2]

  • It soon became clear that the carbon nanotube had the potential to be the building block

  • of futuristic new technologies.

  • The most efficient computers, transformative medical devices, synthetic muscles, or perhaps

  • the most ambitious of all, space elevators, the dream of countless sci-fi authors,

  • Carbon nanotubes has promised to be the catalyst for the next revolution in technology.

  • But, putting this revolutionary material to work will not be easy.

  • It turns out that building a fibre, that is actually a single molecule, of any significant

  • length is incredibly difficult.

  • To understand this fascinating molecule, let’s dive into the chemical makeup of carbon nanotubes.

  • Carbon is a very familiar element.

  • It’s in everything we eat, sleep on and step over.

  • It is the element that holds our DNA together.

  • It forms the carbohydrates, proteins and lipids that we depend on to build and fuel our bodies.

  • It’s the basis of life as we know it.

  • It’s ubiquity in our lives is a result of its versatility.

  • It’s chemical properties allow it to take many different shapes, each impacting it’s

  • material properties in diverse and unique ways.

  • To understand this we need to understand the basic models of how we visualize electron

  • orbits around the nucleus of an atom.

  • To start we have the simplified bohr model, which separates the electrons into shells.

  • The first shell can contain 2 electrons, while the next shell can hold 8.

  • An atom wants to fill each shell to be stable.

  • Let’s take an atom of carbon, which has 6 electrons, to see how this plays out.

  • [3]

  • First we fill the first shell with it’s 2 electrons, then we have 4 electrons left

  • to fill the next shell, leaving 4 open positions in its outer shell

  • The 4 open positions mean that carbon willingly interacts with many other elements as well

  • as itself.

  • Often by sharing electrons in a special type of bond, called a covalent bond.

  • This versatility allows carbon to create many different kinds of molecules.

  • Take hydrocarbons.

  • Hydrogen has 1 electron, and seeks 1 electron to fill it’s inner shell.

  • So, carbon likes to form 4 covalent bonds with 4 hydrogen atoms to form a stable 8 electron

  • outer shell, while helping hydrogen form a stable 2 electron shell.

  • This is methane, an incredibly common molecule that is the main ingredient in natural gas

  • fuels.

  • This is just one arrangement carbon can take.

  • Hydrocarbons take a huge range of shapes and configurations, but what we are interested

  • in is how carbon bonds to itself, but this simplified Bohr model doesn’t give us an

  • understanding of how carbon to carbon bonds take radically different shapes.

  • We need to dive a little deeper before we can understand the magic of carbon nanotubes.

  • Electrons don’t travel in neat 2D circular orbits as the Bohr model would suggest, in

  • fact we can’t even know the position and speed of an electron.

  • Instead we can make predictions about electrons' general locations in 3D space.

  • We call these orbitals, and they are regions where we have about a 90% certainty that an

  • electron is located somewhere within that region.

  • This can get pretty complicated, but for now we just need to concern ourselves with two

  • types.

  • S and P orbitals.

  • [4]

  • S orbitals are spherical in shape with the nucleus of the atom at their centre.

  • P orbitals are often called dumbbell shaped, but I don’t know what gym these nerds are

  • going to, because I have never seen a dumbbell like this.

  • It’s more like a figure of 8 shape like the infinity symbol.

  • In the ground state, electrons will occupy the lowest energy orbitals first, which in

  • this case is the 1S orbital.

  • It can hold two electrons.

  • Next we have the 2S orbital, which is a larger sphere, and can also hold 2 electrons.

  • Then we have our three P orbitals, one aligned along the X, Y and Z axis, each capable of

  • holding 2 electrons.

  • Carbon in its ground state has the 1S and 2S orbitals filled, with one electron in the

  • Px orbital and one in the Py orbital.

  • To be stable, Carbon wants to fill these three p orbitals with 2 electrons each.

  • Now this where things get a little funky and confusing, and it will be on your final exam.

  • Carbon can bond to itself in different ways that affect these orbital shapes.

  • Take diamonds.

  • To fill these orbitals, carbon bonds with 4 neighbouring carbon atoms.

  • To do this it promotes one electron from it’s 2S orbital into the empty Pz orbital.

  • [5] This Pz orbital is higher energy than the 2S orbital, and the electron doesn’t

  • want to stay there, so the carbon atom takes on new hybrid orbital shapes to compensate.

  • This is called sp3 hybridisation, which is a mixture of S and P orbital shapes and looks

  • something like this.

  • Where one side of the figure of 8 expands while the other contracts.

  • The 2S and 3 P orbitals are transformed into these new SP3 orbital shapes.

  • They repel each other equally in this 3D space to form this four lobed tetrahedral shape

  • with 109.5 degrees between each lobe.

  • Covalent bonds now form between the carbon molecules where these orbital lobes overlap

  • head on in what’s called a sigma bond.

  • This creates a repeating structure like this and it’s this rigid framework of carbon

  • atoms that makes diamond extremely hard.

  • Now, what’s fascinating to me, is that you can take the same carbon atoms and now form

  • graphite, a material so soft that we use it as pencil lead and as a lubricant.

  • How does that work?

  • Here a different hybridisation occurs.

  • Once again 1 electron from the 2S orbital is promoted into the Pz orbital, but this

  • time the S orbital hybridizes with only 2 of the P orbitals, giving us the name SP2

  • hybridization.

  • [5] This gives us three SP hybrid orbitals and 1 regular P orbitals.

  • This new arrangement causes the orbitals to take a new shape, with the 3 SP orbitals arranging

  • themselves in a flat plane separated by 120 degrees, with the P orbital perpendicular

  • to them.

  • Now, when the carbon atoms combine, the heads of the SP orbitals overlap once again to form

  • this flat hexagonal shape.

  • A hexagon pattern is naturally a very strong and energy-efficient shape.

  • For example, bees don’t intentionally build honeycombs in hexagons.

  • They form as a result of the warm bee bodies melting the wax and the triple junction hardens

  • in the strongest formation.

  • [6] The shape is frequently used in aerospace applications where high strength and low weight

  • is a priority.

  • These SP2 bonds are stronger than SP3 bonds, because they have a higher s character.

  • This sounds complicated, but all it means is that they are more like S orbitals than

  • a P orbitals.

  • Because there are 3 SP bonds, they have a 33% S character, whereas SP3 orbitals have

  • 4 SP bonds giving them 25% S character.

  • S orbitals are closer to the nucleus, making SP2 bonds shorter and more electronegative

  • than SP3 bonds, and thus stronger.

  • [7]

  • This hexagonal structure and strong bonds make graphene exceedingly strong.

  • Laboratory testing of graphene using atomic force microscopes has shown graphene has a

  • young's modulus of 0.5 TPa and an ultimate tensile strength 130 gigapascals.

  • [8]

  • So strong that if we could somehow create a large perfect sheep of graphene, which we

  • can’t, we could build an invisible single atom deep hammock that could support the weight

  • of a cat.

  • [9] Imagine the amount of cats we could confuse.

  • That’s the world I want to live in.

  • That’s an entertaining, but not terribly useful application, but graphene is a very

  • common material and the form we are used to, graphite, is not strong.

  • This hexagonal shape itself is extremely strong, but because graphite forms these single atom

  • layer sheets with only weak van der waal forces holding them together, the sheets can easily

  • slide over each other, which is the reason graphite is so soft.

  • [10]

  • Now what is interesting is that carbon nanotubes take the same repeating hexagonal structure

  • as graphite.

  • The ends of the sheets are simply loops and connect with themselves to form a tube, and

  • this structure is what gives carbon nanotubes their incredible strength.

  • Researchers found that single-walled nanotubes have strength similar to that of graphite,

  • about 130 Gigapascals.

  • [11]

  • For the non-engineers in the crowd, let me rephrase that.

  • It’s a lot.

  • About 100 times greater than steel, and to boot it’s vastly lighter.

  • If this material could be feasibly manufactured into a single extremely long fibre, it could

  • potentially open up entirely new design possibilities.

  • Like the space elevator.

  • I’d explain exactly why carbon fibres would make space elevators possible now, but I already

  • did that in a past video that I will link at the end of this one.

  • So where are there space elevators?

  • Here lies the difficulty.

  • Manufacturing carbon nanotubes.

  • Carbon nanotubes strength relies on creating a continuous perfect lattice of carbon atoms

  • in a long tube, and that process is not something we have yet developed.

  • So how can we create carbon nanotubes?

  • Things have changed a bit since the days of Sumio Ijima’s first discovery.

  • The most promising method for industrial scale production of high purity carbon nanotubes

  • is chemical vapor deposition.

  • [12]

  • In this manufacturing method, a precursor gas containing carbon, like methane (CH4)

  • is introduced into a vacuum chamber and heated.

  • As the heat increases inside the chamber the bonds between the carbon and hydrogen atoms

  • begin to decompose.

  • The carbon then diffuses into a melted metal catalyst substrate.

  • This then becomes a metal-carbon solution, which eventually becomes supersaturated with

  • carbon.

  • At this point the carbon starts to precipitate out and form carbon nanotubes..

  • While the hydrogen bi-product is vented out of the chamber to avoid an explosion.

  • Our research has focused on increasing the length of these nanotubes while not sacrificing

  • their structure, yield or quantity.

  • While some labs have gotten individual tubes as long as 50 cm it’s been a struggle to

  • get larger bundles of tubes, which are called forests, to a length greater than 2cm. [13]

  • This is because the catalyst is guaranteed to deactivate at some point during the growth

  • process, terminating the growth of the nanotube.

  • The key to growing longer nanotubes is minimizing the probability of the catalyst deactivation

  • [14]

  • In 2020, a research team based in Japan managed to grow a forest over 15 cms in length, 7

  • times longer than anyone else, using a new method of chemical vapor deposition that managed

  • to keep the catalyst active for 26 hours.

  • [15]

  • They did this by adding a layer of gadolinium to a conventional iron-aluminium oxide catalyst

  • coated onto a silicon substrate.

  • Then using a lower chamber temperature, small concentrations of iron and aluminum vapor

  • were added into the chamber.

  • These factors combined managed to keep the iron-aluminium oxide catalyst active for much

  • longer.

  • [16]

  • This method is a major leap forward that could allow carbon nanotube products to begin entering

  • the market, but we are still a long way from a space elevator.

  • Most products today call for the fibres to be woven together to form a textile like yarn.

  • One study I found wove together 1 mm long nanotubes and into a yarn and then impregnated

  • that with an epoxy resin to form a composite material, which had a pretty good tensile

  • strength of 1.6 Gigapascals.

  • [17] Beating aluminium in its strength to weight capabilities, but below a traditional

  • carbon fibre composite.

  • However, these new longer nanotubes may give us stronger woven fibres in future.

  • It’s important to remember that carbon nanotubes aren’t just strong.

  • Their most exciting new term applications will come about as a result of their other

  • material properties.

  • Like their conductive abilities.

  • Like graphite, nanotubes are highly conductive, because each carbon atom is only bonded to

  • 3 other carbon atoms, each atom has 1 free valence electron available for electrical

  • conduction.

  • Making carbon nanotubes excellent conductors.

  • The conducting core of cables that make up our overhead grid lines are typically made

  • from aluminium.

  • Even though aluminium is a poorer conductor than copper, and thus causes a greater loss

  • in power over the lines.

  • It’s used because it’s cheaper and lighter.

  • Allowing support structures for overhead lines to be spaced further apart.

  • Individual nanotubes are orders of magnitudes more conductive than copper, but creating

  • a yarn of nanotubes that could match copper has been a challenge.

  • Electrons move through individual nanotubes very efficiently, but when the tube comes

  • to an end the current meets resistance when jumping to a neighbouring tube.

  • So these longer tubes developed last year are opening doors to conductors that are vastly

  • lighter than aluminium and more conductive than copper.

  • [18]

  • These could be used for grid connections, allowing our power lines to be stretch further

  • without supports and minimize the loss of power to heat resistance, but for now the

  • price of nanotubes likely shuts that door.

  • Instead we could see these wires being used in super lightweight aircraft or cars.

  • They are even being investigated as a means of helping composite structure planes, like

  • the 787, survive lightning strikes.

  • The 787 is primarily composed of carbon and glass fibre reinforced plastics, but because

  • they do not conduct electricity, the plane has additional conductive structures added

  • to protect it from lightning strikes,

  • like a thin copper mesh.

  • [19] This mesh adds weight that increases fuel consumption.

  • This could be drastically reduced by including a carbon nanotube mesh on the surface of the

  • composite instead.

  • Nanotubes are quite elastic.

  • Capable of stretching to 18% of their original length and returning to their original shape