Applications of Nanomaterials
Just a man
Since nanomaterials possess unique, beneficial chemical,
physical, and mechanical properties, they can be used for a wide
variety of applications. These applications include, but are not
limited to, the following:
Next-generation computer chips
The microelectronics industry has been emphasizing
miniaturization, whereby the circuits, such as transistors, resistors,
and capacitors, are reduced in size. By achieving a significant
reduction in their size, the microprocessors, which contain these
components, can run much faster, thereby enabling computations at far
greater speeds. However, there are several technological impediments
to these advancements, including lack of the ultrafine precursors to
manufacture these components; poor dissipation of tremendous amount of
heat generated by these microprocessors due to faster speeds; short
mean time to failures (poor reliability), etc. Nanomaterials help the
industry break these barriers down by providing the manufacturers with
nanocrystalline starting materials, ultra-high purity materials,
materials with better thermal conductivity, and longer-lasting,
durable interconnections (connections between various components in
the microprocessors).
Kinetic Energy (KE) penetrators with enhanced lethality
The Department of Defense (DoD) is currently using depleted-
uranium (DU) projectiles (penetrators) for its lethality against
hardened targets and enemy armored vehicles. However, DU has residual
radioactivity, and hence, is toxic (carcinogenic), explosive, and
lethal to the personnel who use them. However, some of the important
reasons for the continued use of DU penetrators are that they possess
a unique self-sharpening mechanism on impact with a target, and the
lack of suitable non-explosive, non-hazardous replacement for DU.
Nanocrystalline tungsten heavy alloys lend themselves to such a self-
sharpening mechanism because of their unique deformation
characteristics, such as grain-boundary sliding. Hence,
nanocrystalline tungsten heavy alloys and composites are being
evaluated as potential candidates to replace DU penetrators.
Better insulation materials
Nanocrystalline materials synthesized by the sol-gel technique
results in foam like structure called an "aerogel." These aerogels
are porous and extremely lightweight; yet, they can withstand 100
times their weight. Aerogels are composed of three-dimensional,
continuous networks of particles with air (or any other fluid, such as
a gas) trapped at their interstices. Since they are porous and air is
trapped at the interstices, aerogels are currently being used for
insulation in offices, homes, etc. By using aerogels for insulation,
heating and cooling bills are drastically reduced, thereby saving
power and reducing the attendant environmental pollution. They are
also being used as materials for "smart " windows, which darken when
the sun is too bright (just as in changeable lenses in prescription
spectacles and sunglasses) and they lighten themselves, when the sun
is not shining too brightly.
Phosphors for high-definition TV
The resolution of a television, or a monitor, depends greatly
on the size of the pixel. These pixels are essentially made of
materials called "phosphors," which glow when struck by a stream of
electrons inside the cathode ray tube (CRT). The resolution improves
with a reduction in the size of the pixel, or the phosphors.
Nanocrystalline zinc selenide, zinc sulfide, cadmium sulfide, and lead
telluride synthesized by the sol-gel technique are candidates for
improving the resolution of monitors. The use of nanophosphors is
envisioned to reduce the cost of these displays so as to render high-
definition televisions (HDTVs) and personal computers affordable to be
purchased by an average household in the U. S.
Low-cost flat-panel displays
Flat-panel displays represent a huge market in the laptop
(portable) computers industry. However, Japan is leading this market,
primarily because of its research and development efforts on the
materials for such displays. By synthesizing nanocrystalline
phosphors, the resolution of these display devices can be greatly
enhanced, and the manufacturing costs can be significantly reduced.
Also, the flat-panel displays constructed out of nanomaterials possess
much higher brightness and contrast than the conventional ones owing
to their enhanced electrical and magnetic properties.
Tougher and harder cutting tools
Cutting tools made of nanocrystalline materials, such as tungsten
carbide, tantalum carbide, and titanium carbide, are much harder, much
more wear-resistant, erosion-resistant, and last longer than their
conventional (large-grained) counterparts. They also enable the
manufacturer to machine various materials much faster, thereby
increasing productivity and significantly reducing manufacturing
costs. Also, for the miniaturization of microelectronic circuits, the
industry needs microdrills (drill bits with diameter less than the
thickness of an average human hair or 100 m) with enhanced edge
retention and far better wear resistance. Since nanocrystalline
carbides are much stronger, harder, and wear-resistant, they are
currently being used in these microdrills.
Elimination of pollutants
Nanocrystalline materials possess extremely large grain
boundaries relative to their grain size. Hence, nanomaterials are
very active in terms of their of chemical, physical, and mechanical
properties. Due to their enhanced chemical activity, nanomaterials
can be used as catalysts to react with such noxious and toxic gases as
carbon monoxide and nitrogen oxide in automobile catalytic converters
and power generation equipment to prevent environmental pollution
arising from burning gasoline and coal.
High energy density batteries
Conventional and rechargeable batteries are used in almost all
applications that requires electric power. These applications include
automobiles, laptop computers, electric vehicles, next-generation
electric vehicles (NGEV) to reduce environmental pollution, personal
stereos, cellular phones, cordless phones, toys, and watches. The
energy density (storage capacity) of these batteries is quite low
requiring frequent recharging. The life of conventional and
rechargeable batteries is also low. Nanocrystalline materials
synthesized by sol-gel techniques are candidates for separator plates
in batteries because of their foam-like (aerogel) structure, which can
hold considerably more energy than conventional ones. Furthermore,
nickel-metal hydride (Ni-MH) batteries made of nanocrystalline nickel
and metal hydrides are envisioned to require far less frequent
recharging and to last much longer because of their large grain
boundary (surface) area and enhanced physical, chemical, and
mechanical properties.
High-power magnets
The strength of a magnet is measured in terms of coercivity
and saturation magnetization values. These values increase with a
decrease in the grain size and an increase in the specific surface
area (surface area per unit volume of the grains) of the grains. It
has been shown that magnets made of nanocrystalline yttrium-samarium-
cobalt grains possess very unusual magnetic properties due to their
extremely large surface area. Typical applications for these high-
power rare-earth magnets include quieter submarines, automobile
alternators, land-based power generators, motors for ships, ultra-
sensitive analytical instruments, and magnetic resonance imaging (MRI)
in medical diagnostics.
High-sensitivity sensors
Sensors employ their sensitivity to the changes in various
parameters they are designed to measure. The measured parameters
include electrical resistivity, chemical activity, magnetic
permeability, thermal conductivity, and capacitance. All of these
parameters depend greatly on the microstructure (grain size) of the
materials employed in the sensors. A change in the sensor's
environment is manifested by the sensor material's chemical, physical,
or mechanical characteristics, which is exploited for detection. For
instance, a carbon monoxide sensor made of zirconium oxide (zirconia)
uses its chemical stability to detect the presence of carbon
monoxide. In the event of carbon monoxide's presence, the oxygen
atoms in zirconium oxide react with the carbon in carbon monoxide to
partially reduce zirconium oxide. This reaction triggers a change in
the sensor's characteristics, such as conductivity (or resistivity)
and capacitance. The rate and the extent of this reaction are greatly
increased by a decrease in the grain size. Hence, sensors made
nanocrystalline materials are extremely sensitive to the change in
their environment. Typical applications for sensors made out of
nanocrystalline materials are smoke detectors, ice detectors on
aircraft wings, automobile engine performance sensor, etc.
Automobiles with greater fuel efficiency
Currently, automobile engines waste considerable amounts of
gasoline, thereby contribute to environmental pollution by not
completely combusting the gas. A conventional spark plug is not
designed to burn the gasoline completely and efficiently. This
problem is compounded by defective, or worn-out, spark plug
electrodes. Since nanomaterials are stronger, harder, and much more
wear-resistant and erosion-resistant, they are presently being
envisioned to be used as spark plugs. These electrodes render the
spark plugs longer-lasting and combust fuel far more efficiently and
completely. A radically new spark plug design called the "railplug"
is also in the prototype stages. This railplug uses the technology
derived from the "railgun," which is a spin-off of the popular Star
Wars defense program. However, these railplugs generate much more
powerful sparks (with an energy density of approximately 1 kJ/mm2).
Hence, conventional materials erode and corrode too soon and quite
frequently to be of any practical use in automobiles. Nevertheless,
railplugs made of nanomaterials last much longer even the conventional
spark plugs. Also, automobiles waste significant amounts of energy by
losing the thermal energy generated by the engine. This is especially
true in the case of diesel engines. Hence, the engine cylinders
(liners) are currently being envisioned to be coated with
nanocrystalline ceramics, such as zirconia and alumina, so that they
retain heat much more efficiently and result in complete and efficient
combustion of the fuel.
Aerospace components with enhanced performance characteristics
Due to the risks involved in flying, aircraft manufacturers
strive to make the aerospace components stronger, tougher, and last
longer. One of the key properties required of the aircraft components
is the fatigue strength, which decreases with the component's age. By
making the components out of stronger materials, the life of the
aircraft is greatly increased. The fatigue strength increases with a
reduction in the grain size of the material. Nanomaterials provide
such a significant reduction in the grain size over conventional
materials that the fatigue life is increased by an average of
200-300%. Furthermore, components made of nanomaterials are stronger
and can operate at higher temperatures, aircrafts can fly faster and
more efficiently (for the same amount of aviation fuel). In
spacecrafts, elevated-temperature strength of the material is crucial
because the components (such as rocket engines, thrusters, and
vectoring nozzles) operate at much higher temperatures than aircrafts
and higher speeds. Nanomaterials are perfect candidates for spacecraft
applications, as well.
Better and future weapons platforms
Conventional guns, such as cannons, 155 mm howitzers, and
multiple-launch rocket system (MLRS), utilize the chemical energy
derived by igniting a charge of chemicals (gun powder). The maximum
velocity at which the penetrator can be propelled is approximately
1.5-2.0 km/sec. On the other hand, electromagnetic launchers (EML
guns), or railguns, use the electrical energy, and the concomitant
magnetic field (energy), to propel the penetrators/projectiles at
velocities up to 10 km/sec. This increase in velocity results in
greater kinetic energy for the same penetrator mass. The greater the
energy, the greater is the damage inflicted on the target. For this
and other reasons, the DoD (especially, the U. S. Army) has conducted
extensive research into the railguns. Since a railgun operates on
electrical energy, the rails need to be very good conductors of
electricity. Also, they need to be so strong and rigid that the
railgun does not sag while firing and buckle under its own weight.
The obvious choice for high electrical conductivity is copper.
However, the railguns made out of copper wear out much too quickly due
to the erosion of the rails by the hypervelocity projectiles and they
lack high-temperature strength. The wear and erosion of copper rails
necessitate inordinately frequent barrel replacements. In order to
satisfy these requirements, a nanocrystalline composite material made
of tungsten, copper, and titanium diboride is being evaluated as a
potential candidate. This nanocomposite possesses the requisite
electrical conductivity, adequate thermal conductivity, excellent high
strength, high rigidity, hardness, and wear/erosion resistance. This
results in longer-lasting, wear-resistant, and erosion-resistant
railguns, which can be fired more frequently and often than their
conventional counterparts.
Longer-lasting satellites
Satellites are being used for both defense and civilian
applications. These satellites utilize thruster rockets to remain in
or change their orbits due to a variety of factors including the
influence of gravitational forces exerted by the earth. Hence, these
satellites are repositioned using these thrusters. The life of these
satellites, to a large extent, is determined by the amount of fuel
they can carry on board. In fact, more than 1/3 of the fuel carried
aboard by the satellites is wasted by these repositioning thrusters
due to incomplete and inefficient combustion of the fuel, such as
hydrazine. The reason for the incomplete and inefficient combustion
is that the onboard ignitors wear out quickly and cease to perform
effectively. Nanomaterials, such as nanocrsytalline tungsten-titanium
diboride-copper composite, are potential candidates for enhancing
these ignitors' life and performance characteristics.
Longer-lasting medical implants
Currently, medical implants, such as orthopedic implants and
heart valves, are made of titanium and stainless steel alloys. These
alloys are primarily used in humans because they are bio-compatible,
i. e., they do not adversely react with human tissue. In the case of
orthopedic implants (artificial bones for hip, etc.), these materials
are relatively non-porous. For an implant to effectively mimic a
natural human bone, the surrounding tissue must penetrate the
implants, thereby affording the implant with the required strength.
Since these materials are relatively impervious, human tissue does not
penetrate the implants, thereby reducing their effectiveness.
Furthermore, these metal alloys wear out quickly necessitating
frequent, and often very expensive, surgeries. However,
nanocrystalline zirconia (zirconium oxide) ceramic is hard, wear-
resistant, corrosion-resistant (biological fluids are corrosive), and
bio-compatible. Nanoceramics can also be made porous into aerogels
(aerogels can withstand up to 100 times their weight), if they are
synthesized by sol-gel techniques. This results in far less frequent
implant replacements, and hence, a significant reduction in surgical
expenses. Nanocrystalline silicon carbide (SiC) is a candidate
material for artificial heart valves primarily due to its low weight,
high strength, extreme hardness, wear resistance, inertness (SiC does
not react with biological fluids), and corrosion resistance.
Ductile, machinable ceramics
Ceramics, per se, are very hard, brittle, and hard to
machine. These characteristics of ceramics have discouraged the
potential users from exploiting their beneficial properties. However,
with a reduction in grain size, these ceramics have increasingly been
used. Zirconia, a hard, brittle ceramic, has even been rendered
superplastic, i. e., it can deformed to great lengths ( up to 300% of
its original length). However, these ceramics must possess
nanocrystalline grains to be superplastic. In fact, nanocrystalline
ceramics, such as silicon nitride (Si3N4) and silicon carbide (SiC),
have been used in such automotive applications as high-strength
springs, ball bearings, and valve lifters, because they possess good
formability and machinabilty combined with excellent physical,
chemical, and mechanical properties. They are also used as components
in high-temperature furnaces. Nanocrystalline ceramics can be pressed
and sintered into various shapes at significantly lower temperatures,
whereas it would be very difficult, if not impossible, to press and
sinter conventional ceramics even at high temperatures.
Large electrochromic display devices
An electrochromic device consists of materials in which an
optical absorption band can be introduced, or an existing band can be
altered by the passage of current through the materials, or by the
application of an electric field. Nanocrystalline materials, such as
tungstic oxide (WO3.xH2O) gel, are used in very large electrochromic
display devices. The reaction governing electrochromism (a reversible
coloration process under the influence of an electric field) is the
double-injection of ions (or protons, H+) and electrons, which combine
with the nanocrystalline tungstic acid to form a tungsten bronze.
These devices are primarily used in public billboards and ticker
boards to convey information. Electrochromic devices are similar to
liquid-crystal displays (LCD) commonly used in calculators and
watches. However, electrochromic devices display information by
changing color when a voltage is applied. When the polarity is
reversed, the color is bleached. The resolution, brightness, and
contrast of these devices greatly depend on the tungstic acid gel's
grain size. Hence, nanomaterials are being explored for this
purpose.
From the above examples, it is quite evident that
nanocrystalline materials, synthesized by the sol-gel technique, can
be used in a wide variety of new, unique and existing applications.
It is also very evident that nanomaterials outperform their
conventional counterparts because of their superior chemical,
physical, and mechanical properties and of their exceptional
formability.
The aforementioned are only a few applications of
nanocrysytalline materials or nanomaterials. Many new applications are
being discovered almost daily. There are many other applications and
uses, which have yet to be discovered. For more information, please
contact NANOMAT.