Advanced & Exotic Materials


Now, we will talk about some of the advanced
materials. So, we have seen the basic materials and the
advanced category, we keep those materials which are just coming up their use, so mostly
from the laboratory, they are just getting rolled out and they are used in certain very
high-performance applications. One of them is the smart material as you can
see here that there are various groups of smart materials. I will talk about them later on like piezoelectric,
magnetostrictive, phase transition dependent or Electro/Magneto Rheological Materials. Now in all these materials, the reason why
they are called smart materials is that they do something more than a simple you know coupling
with the stress and the strain in the sense that every material if you apply force it
deforms. But not many materials will actually deform
with the application of let us say electric field or say magnetic field or say you know
light itself temperature or say, not many materials will change their viscosity with
respect to the change of electric field or magnetic field. These are the group of materials which have
very good use in terms of making sensors in terms of making artificial muscles, etc. And they are covered as smart materials, so
that the one group of materials that has just you know that are just coming up. The other groups of material, which are becoming
very popular are actually biomaterials. Now they are the materials which are actually
getting linked or coupled with the living system itself. For example, you think of the artificial joints,
you think of the bone replacement, you think of artificial tendons, you think of dental
implants or something which changes the blood vessels, heart valves, skin repairing, cochlear
implant, contact lens, what not our entire human body. In fact, if you go through some of the science
fictions you would see that a person is depicted is of 300 years of age and the person is telling
you know there is hardly anything now in my body which is having kind of genetic origin,
which is something which I got from my biological parents, everything got gradually replaced
by actually engineering materials. Now that is the way towards which we are advancing. We would see that all the joints today are
getting replaced by engineering materials. Our eyes are getting replaced by these you
know the synthetic eyes like the specs and similarly the various parts of the body. So that is the biomaterials and that are actually
becoming very-very important into this context. Now, biomaterials could be materials, could
be nonmetals that means ceramics and other things or polymers. So for metals, you have chromium alloys, stainless
steel, that essentially important thing here is that the material should not react with
the living tissues. So some of the very important applications
are for example, the stent which saves you know a lot of life today, right. So what is this stent technology? Here, we are talking about a material which
at a particular temperature, you know blood is warmer, so at a particular temperature
it actually expands and then through that expansion it actually there is some place
where there is constriction in the blood vessel, it tries to actually clear up that constriction,
so that is one type of also smart material, but it is a biological material. Then of course there is implants in terms
of dental implants. You have the prosthesis in terms of a fracture
of bones where it is used for the hip implants, so metals are used very much, some of the
metals are very well accepted inside the body and they are used in terms of prosthetic systems
that is one of the important biological materials. The other groups of the polymers which are
also used in orthopedic applications but more in terms of say artificial tendons or say
you know artificial skins, tendons or grafts, facial and soft tissue reconstruction. There are these methacrylates for example
which are coming up in the big way, then scaffolds for building the tissues or wound dressing
for example or retinal implant or contact lens, this is where the polymers are mostly
used. Then there comes the ceramics, so ceramic
you would see again in prosthetic in terms of mostly as a joint because I told you that
one of the most important property of the ceramics is that its coefficient of friction
is quite low, it is almost like a can work like a frictionless material almost and that
is very good in the joint. So they are used in joints in various types
of joints, in knee joints, in shoulders, etc., so that is one of the good things and also
where you need a high compressive strength for example, for dental you know prosthesis,
ceramics are used in a very large manner. Then there comes a very interesting type of
a material, so that is so far I talked about the biomaterials and the smart materials. This one that I am talking about is called
Aerogel. Aerogel is a material which is like 90 to
98% porous; it is very highly porous. And they are produced by extracting the liquid
component of a gel through a supercritical drying process which extracts all the moisture
out. And once you do that, then the air molecules
that get trapped in the gel would act as insulators and its heat conductivity will be almost close
to 0. They are nowadays getting used in terms of
thermal barrier, thermal insulators and acoustic insulations, etc. That is about the aerogels. (Aerogel demonstration) I told you that aerogels are highly porous,
it is so porous and lightweight that see for example this salt like material that you can
see here which is an aerogel, just disturb it a little bit and you will see that almost
it looks like a liquid why it is basically highly porous, we have to give it some time
so that it will actually settle down. So that is the level of porosity in the system. Now this porosity has a very wonderful application. Because of this high porosity, they can actually
interrupt air inside them and hence they become an excellent thermal insulator for example,
you know this is like the same material we have developed heat foam, out of it. And you see there is a heater here and it
is very hot that you will not be able to keep your hand, it is full-fledged condition. But if you keep the material, the area where
you will keep this material, you can actually very easily keep your hand there, so it can
work very well in terms of heat insulation. So that is the beauty of one of this advance
material which is the Aerogels. Then there is another group of materials which
are known as superconductors. These are much better than the metals why
because they conduct electricity without any resistance. And if there is no resistance, means there
is hardly any loss of electricity, but they are costly because of the cryogenic requirements. So they have 2 very important effects, one
is the Meissner effect which can be used in terms of magnetic levitation. And another is the Josephson effect, which
can be used in terms of for example fuel cells, etc., where you can have without any you know
voltage generation and voltage you know EMF, you can actually pass electricity if you keep
superconducting elements in between if you keep an insulating film, that is the Josephson
effect. So superconductors are the dream for tomorrow’s
technology. And then one of the most fascinating things
is the Carbon Nanotubes, is developed in 1991 but in various forms in fact as CNT first
may be in terms of fullerene structure there is a Nobel Prize and then there is the graphene,
people got Nobel Prize, so this is something that has actually, that has a promise to revolutionize
everything. I will talk about the power of the Carbon
Nanotubes also at a later stage when will talk about a very specific development in
terms of a space structure. Now these carbon Nanotubes are actually, they
are essentially carbon atoms which are linked in hexagonal shapes. And as you know the Carbon bond, covalent
bond is one of the strongest bond available in nature and this strongest bond is actually
used completely by the Carbon nanotube. And hence it is the strongest and the stiffest
material available in the nature, something like which is hundred times stronger than
steel. It also has very high degree of thermal conductivity
and electrical conductivity. So together with all the very good properties,
CNTs are going to be one of the most important materials for building tomorrow’s technology. Now this is where you know I am bringing the
whole discussion to an end. In the next lecture we will talk about the
basic concept of stress and strain and the group of mechanical properties like the, tensile
strength, ductility, brittleness, resilience, toughness, impact strength, a basic understanding
of it, this is where we will bring an end. Thank you. Keywords- Nature and Properties of Materials,
smart materials, piezoelectric, magnetostrictive, shape memory alloys, SMA, aerogels, CNT, fullerene,
bio materials

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