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the Nebula and CuriosityStream deal for the amazingly low price of 14.79 a year. 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 after. This could allow conductive carbon fibre wires
to be incorporated into wearable technology. The carbon fibre threads can even be treated
like a normal thread and sewn into a fabric using a sewing machine. Perhaps the most exciting application is in
biomedical devices. [20] Carbon nanotubes are biocompatible. Meaning they are not toxic, non reactive,
and do not elicit an immune response. Combine this with their conductivity,flexibility
and strength, nanotubes become extremely attractive as neural interface material. A large part of Neuralink, Elon Musk’s neural
interface companies, efforts have been focusing on creating smaller wires and the machines
needed to implant them. Larger, stiffer wires tear into flexible brain
tissue over time and causes scar tissue to form around the wire, preventing signals from
passing from the neurons to the wires. Nanotube wiring could be made smaller and
more flexible while being accepted by the body. A potentially game changing material for biomedical
implants. As with every major material innovation, from
age hardened aluminium ushering in a new age of aviation, to silicon semiconductors opening
up an entire new world for computers, carbon nanotubes have the potential to open the door
to design possibilities and technologies we have yet to imagine. New materials radically change how and what
we build, and learning more about manufacturing processes for complex machines really gives
you insight on how a material like this could change things. One of my favourite series on CuriosityStream. How to Build teaches you exactly that. An in depth series that takes you onto the
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It's a bummer that they seem to lose a lot of their tensile strength when baked into a resin, but the conductivity advantage still sounds pretty awesome if they can be made cheap enough (although I imagine you'd have to insulate them pretty good to keep them away from any potential fire).