Unit 3 Revision Questions

Part A (2marks)

1. Define Nanomaterials.
Ans: Nanomaterials are defined as the materials having a size of roughly 1 to 100
nanometers.
2. Classify nanomaterial based on their dimension.
Ans: On the basis of the dimensions, nanomaterials can be divided into :
a)zero dimensional---Eg:Gold nanoparticle, quantum dot etc
b) one dimensional---Eg:metal rods, carbon nanotube, gold nanowire etc
c) two dimensional –Eg: carbon coated nanoplates, graphene sheet etc
d) three- dimensional –Eg polycrystalline material, dendrimer etc
3. What is magic number?
Ans: Magic number is the number of atoms in the clusters of critical sizes with higher
stability.
4. What are Nano rods? Give an example.
Ans: Nanorods are one dimensional nanostructures, shaped like long sticks rods.
Examples: Zinc oxide, Cadmium sulphide, Gallium nitride nano rods.
5. Write the important applications of Nanotubes?
Ans:
1. Nanotubes can potentially replace indium, tin oxide in solar cells to generate
photocurrent.
2. Single walled nanotubes are used in transistors and solar panels
3. Multiwall nanotubes are used in lithium ion batteries to enhance cycle life.
6. List any four nanomaterials.
 Ans: Carbon-based nanomaterials
 Metal-based nanomaterials
 Dendrimers
 Nanocomposites
7. Differentiate quantum well and quantum dot.
Ans:
Quantum Well Quantum Dot
It is a two-dimensional system It is a zero-dimensional system
The electrons can move in two directions The electron movements are restricted in entire
and restricted in one direction three directions

8. Define ablation rate.

Ans: The total mass ablated from the target per laser pulse during the laser ablation
synthesis of nanomaterials is usually referred to as ablation rate.
 Part B (13marks)

1. Enumerate the difference between atoms, bulk materials and nanomaterials.

PROPERTY ATOMS/ NANOMATERIALS BULK MATERIALS

MOLECULES
Size Few angstrom(10^-10 Nanometres (10^-9 m) Microns to higher
m) (10^-6 m)

No.of One atom to few / Few atoms to several Infinite / of the order of
constituent many atoms thousand of atoms Avogadro number
particles
Electronic confined confined Not confined(continuous)
structure
Mechanical NA Properties depend on Properties independent of
properties particle size particle size
Wave nature applicable applicable Applicable to limited
extend
Random present present Not present
motion
Stability stable Can be stable or Stable
unstable depending on
surface energy
Geometric Well - defined Well – defined structure Crystal structure
structure structure and and predictable
predictable
Interaction Chemical forces Strong interactions at Interactions include bulk
the nanoscale forces like gravity
Conductivity - Enhanced thermal and May vary across the
electrical conductivity at material
the nanoscale
Phase Changes in state Nanoscale materials Based on temperature and
transitions common may exhibit unique pressure.
 phase transitions
Applications Studied in chemistry Diverse applications in Wide range from
and biology medicine , electronics , construction to electronics
catalysis
Example NaCl , CO2 Carbon nanotube Gold bar , silver bar

2. Explain nanorods, nanoclusters and nanowires with an example. Give its applications.

Nanorods

 Nanorods are two-dimensional cylindrical solid materials with an aspect ratio (length-to-
width ratio) of less than 20.

 Examples: Zinc oxide, Cadmium sulphide, Gallium nitride nanorods.

Synthesis of Nanorods

 Chemical synthesis is used to produce nanorods.

 Ligands act as shape control agents, binding with varying strengths to different facets of
the nanorod.
 This differential bonding controls the growth rate along each axis, resulting in an
elongated shape.
 Commercial production of some nanorods is limited due to low demand.

Properties of Nanorods

1. Two-dimensional structure.
2. Exhibit optical and electrical properties.

Applications of Nanorods

1. Display technologies.
2. Manufacturing of micro-mechanical switches.
3. Used in micro-electro-mechanical systems (MEMS) and under applied electric fields.
4. Function as theragnostic agents when combined with noble metal nanoparticles.
5. Used in energy harvesting and light-emitting devices.
6. Serve as cancer therapeutics

Nanowires

 Nanowires are two-dimensional cylindrical solid materials with an aspect ratio (length-to-
width ratio) greater than 20.
 The diameter of nanowires typically ranges from 10 – 100 nm.
Examples of Nanowires
S.No Types of Nanowires Examples

1 Metallic nanowires Au (Gold), Ni (Nickel), Pt (Platinum)

2 Nanowires of semiconductors InP (Indium Phosphide), Si (Silicon), GaN (Gallium Nitride)

3 Nanowires of insulators SiO₂ (Silicon Dioxide), TiO₂ (Titanium Dioxide)

4 Molecular nanowires DNA

Synthesis of Nanowires

1. Template-Assisted Synthesis
o A simple method for fabricating nanowires by using templates with cylindrical
pores or voids.
o The empty spaces within the template are filled with the chosen material, forming
nanowires.

2. VLS (Vapour-Liquid-Solid) Method

o The source material is absorbed from the gas phase into a liquid phase catalyst.
o When the liquid alloy becomes supersaturated, a solid precipitate forms, acting as
a nucleation site.
o This nucleation seed promotes further deposition of material, resulting in the
elongation of the nanowire.

Properties of Nanowires

1. Two-dimensional structure.
2. Conductivity is lower than that of the corresponding bulk material.
3. Exhibit distinct optical, chemical, thermal, and electrical properties due to their large
surface area.
4. Silicon nanowires show strong photoluminescence.

Uses of Nanowires

1. Enhance the mechanical properties of composites.

2. Used to create active electronic components such as p-n junctions and logic gates.
3. Play a crucial role in the future of digital computing through semiconductor nanowire
crossings.
4. Used in high-density data storage applications, such as magnetic read heads and patterned
storage media.
5. Replace conventional copper wires in computers and televisions.
6. Enable the linking of tiny components into ultra-small circuits.
Nanoclusters

Definition

 Nanoclusters are fine aggregates of atoms or molecules with sizes ranging from 0.1 to 10
nm.
 Among all nanomaterials, nanoclusters are the smallest due to the close packing
arrangement of atoms.

Examples: CdS (Cadmium Sulfide), ZnO (Zinc Oxide)

Forces in Nanoclusters

 The atoms within nanoclusters are held together by metallic, covalent, ionic, hydrogen
bonds, or van der Waals forces.
 Clusters of critical sizes exhibit higher stability than others.
 Nanoclusters with up to a few hundred atoms are distinct from larger nanoparticles,
which contain 10³ or more atoms.

Magic Number

 The Magic Number refers to the number of atoms in clusters of critical size that show
higher stability.
 The type of forces between atoms determines the properties of different nanoclusters.
 Clusters containing transition metals exhibit unique chemical, electronic, and magnetic
properties, which vary based on:
o Number of atoms
o Type of elements
o Net charge of the cluster

Production of Nanoclusters

 Nanoclusters can be produced using either:

1. Bottom-up process: Building clusters from atomic or molecular components.
2. Top-down process: Breaking down bulk materials into smaller nanoclusters.

Properties of Nanoclusters

1. Atomic or molecular clusters are formed through the nucleation of atoms or molecules.
2. Reactivity decreases with decreasing size.
3. Melting point is lower compared to bulk materials due to a high surface-to-volume ratio.
4. Electronic structure is more confined than in bulk materials.

Applications of Nanoclusters

1. Used as catalysts in chemical reactions.

 2. Serve as key components in nano-based chemical sensors.
3. Used as light-emitting diodes (LEDs) in quantum computers.

3. Write detail notes on properties of nanomaterials including size dependent properties.

Size-Dependent Properties of Nanomaterials

Nanomaterials exhibit different properties from their bulk counterparts due to:

 Large surface area, making them more chemically reactive and altering strength and
electrical properties.
 Quantum effects dominate at the nanoscale, affecting properties such as melting point,
boiling point, band gap, optical, mechanical, and magnetic properties.
 Increased grain boundaries or interfaces lead to changes in defect dynamics.
 Elastic properties differ from bulk materials due to a higher fraction of defects.

Thermal Properties (Melting Points)

 Nanomaterials have a lower melting point or phase transition temperature compared to

bulk materials due to:
1. Reduced lattice spacing between atoms.
2. A higher fraction of surface atoms relative to the total atom count.
 Decreasing crystal size → Increased surface energy → Decreased melting point.

Example:

 Melting point of CdSe (3 nm): 700 K

 Bulk CdSe: 1678 K

Optical Properties (Absorption and Scattering of Light)

 Quantum confinement of electrons alters energy levels, affecting optical properties.

 Properties depend on size, shape, surface characteristics, and interaction with the
environment.

Example:

 Bulk gold: Yellow color

 Nano-gold: Orange (80 nm), Red (20 nm), or Purple based on size
 Semiconductor nanoparticles: Optical absorption peak shifts to shorter wavelengths due
to an increased band gap.
 Metallic nanoparticles: Color changes with size due to surface plasmon resonance.

Magnetic Properties
  Magnetic behavior differs at the nanoscale: Ferromagnetic materials can become
superparamagnetic as particle size decreases due to large surface area.

Example:
Material Bulk Nanoscale

Fe, Co, Ni Ferromagnetic Superparamagnetic

Na, K Paramagnetic Ferromagnetic

Mechanical Properties

 Nanomaterials have fewer defects than bulk materials, increasing their strength.
 They are stronger, harder, wear-resistant, and corrosion-resistant, making them suitable
for spark plugs and micro-drills.

Example:

 Nano-crystalline carbides: Stronger, harder, and more wear-resistant than bulk carbides.

Electrical Properties

 Electrical conductivity decreases with smaller dimensions due to surface scattering but
can improve with better micro-structural ordering.
 Nanomaterials are ideal for separator plates in batteries due to their ability to store more
energy than bulk materials.

Example:

 Nickel-metal hydride batteries with nanocrystalline nickel and metal hydride require less
frequent recharging and have a longer lifespan.

4. Discuss the applications of nanomaterials.

Applications of Nanomaterials

Nanomaterials find applications in multiple fields due to their unique properties, such as large
surface area, quantum effects, enhanced mechanical strength, and magnetic behavior at the
nanoscale. Below are the key applications:
1. Medicine and Healthcare

 Drug Delivery: Deliver drugs precisely to targeted cells, reducing side effects.
 Cancer Therapy: Gold and iron oxide nanoparticles are used in theragnostics.
 Antimicrobial Coatings: Nanomaterials like silver nanoparticles are used in wound
dressings and hospital equipment to prevent infections.

2. Electronics

 Nano-transistors: Essential for the development of smaller, faster, and more energy-
efficient electronic devices.
 Semiconductor Nanowires: Used in logic gates, p-n junctions, and future digital
computing.
 Display Technologies: Quantum dots improve brightness and color fidelity in LED
displays and TVs.

3. Energy

 Batteries and Supercapacitors: Nanocrystalline materials are used in nickel-metal hydride

batteries for increased capacity and longer lifespan.
 Solar Cells: Nanomaterials like TiO₂ improve solar energy absorption, enhancing the
efficiency of solar cells.
 Energy Harvesting: Nanorods and nanowires are utilized in piezoelectric devices to
convert mechanical energy into electrical energy.

4. Environmental Applications

 Water Purification: Nanomaterials are used for removing heavy metals and pollutants
from water through filtration and adsorption techniques.
 Air Filtration: Nanoscale filters trap pollutants and fine particles for cleaner air.
 Oil Spill Cleanup: Magnetic nanomaterials are employed to efficiently collect spilled oil
from water.

5. Automotive Industry

 Fuel Additives: Nanomaterials improve combustion efficiency and reduce emissions.

 Coatings: Nanomaterial-based coatings enhance wear resistance, corrosion resistance,
and reduce friction in engines.
 Tires: Nano-clays and carbon nanomaterials enhance strength and durability of tires.

6. Aerospace and Defense

 Lightweight Materials: Nano-composites are used to create lighter and stronger materials
for aircraft and spacecraft.
 Stealth Technology: Nanomaterials absorb radar waves, helping create stealth coatings
for military vehicles.
 7. Cosmetics and Personal Care
 Sunscreens: Zinc oxide and titanium dioxide nanoparticles offer UV protection while
remaining transparent on the skin.

 Anti-aging Products: Nanoparticles deliver active ingredients deeper into the skin for
improved efficacy.

8. Chemical Sensors

 Nanomaterials are used in chemical sensors for detecting toxic gases, pollutants, and
biological agents.
 These sensors are highly sensitive and selective due to the large surface area of
nanomaterials.

9. Catalysis

 Nanoclusters and nanoparticles serve as catalysts for chemical reactions by providing

more reactive sites.
 They are used in industrial processes such as the hydrogenation of oils and fuel cell
reactions.

10. Construction and Infrastructure

 Self-cleaning Surfaces: Nano-coatings on windows and surfaces repel dust and dirt.
 Concrete Additives: Nanoparticles improve the strength, durability, and flexibility of
concrete.

5. Describe the synthesis of nanomaterials by precipitation method and thermolysis

method.

Precipitation

 Generally nano-particles are synthesised by the precipitation reaction between the

reactants in presence of water soluble inorganic stabilizing agent.

Examples

1. Precipitation of BaSO4 Nano-particles

 10 gm of sodium hexameta-phosphate (stabilizing agent) was dissolved in 80 ml of

distilled water in 250 ml beaker with constant stirring.
 Then 10 ml of 1M sodium sulphate solution was added followed by 10 ml of 1M
Ba(NO3)2 solution.
 The resulting solution was stirred for 1 hr.
 Precipitation occurs slowly.
  The resulting precipitate was then centrifuged, washed with distilled water and vacuum
dried.

Note : In the absence of stabilizing agent, Bulk BaSO4 is obtained.

2. Precipitation by reduction

 Reduction of metal salt to the corresponding metal atoms.

 These atoms act as nucleation centres leading to formation of atomic clusters.
 These clusters are surrounded by stabilizing molecule that prevent the atoms
agglomerating.
 Example

Nanoparticles of molybdenum can be produced from MoCl₂ in toluene solution

using NaBH (C2H5)3 as a reducing agents at room temperature.

A) Solvothermal synthesis

 A "solvothermal reaction can be defined as a chemical reaction (or a transformation)

between precursor(s) in a solvent (in a close system) at a temperature higher than the
boiling temperature of this solvent and under high pressure".

 The Solvothermal method is identical to the hydrothermal method except that a variety of
solvents other than water can be used for this process.
 This method has been found to be a versatile route for the synthesis of a wide variety of
nanoparticles with narrow size distributions, particularly when organic solvents with high
boiling points are chosen.
 It is a method for preparing a variety of materials such as metals, semiconductors,
ceramics, and polymers.
 Solovothermal are usually thick walled steel cylinders with hermetic seal which must
withstand high temperature and pressure for prolonged periods of times.
 The autoclave material must be inert with respect to the solovent.
 The closure is the most important element of the autoclave.
 To prevent corroding of the internal cavity of the autoclave, prodective inserts are
genrally used.
 These may have the same shape of the autoclave and fit in the internal cavity.
 Inserts may be made up of carbon free iron, glass or quarts, copper or Teflon depending
on the temperature and material used.
 The process involves the use of a non-aqueous solvent under moderate to high pressure
(typically between 1 atm and 10,000 atm) and temperature (typically between 100 °C and
1000 °C) that Facilitates the interaction between reactants during synthesis.
 High temperature and pressure facilitates the dissolution of the reactants and products are
generally obtained in the nanocrystalline form.
 It is then washed and then dried.
 Example - 1:- Nano crystal of CdSe have been prepared by reacting cadmium stereate
with selenium powder using toluene as solvent, tetrahydro phenolphthalein as reducing
agent.
 Example - 2:- Cadmium oxalate and chalcogens undergo reaction in presence of pyridine
as solvent to produce cadmium nanoparticle.
E = Chalcogenide( S,Se, Te)

Advantages:

 Relatively easy and cheap method.

 Products obtained are in crystalline form. So no purification required.
 Can be used for preparing nanomaterials of different morphology (powder, rod, wire,
tube, single crystals and nanocrystals).
 Precise control over the size, shape distribution and crystallinity of nanoparticles by
varying experimental conditions.
 Variety of organic solvents can be used as it helps the dispersion nanocrystallites and
may stabilize some metastable phases.

Disadvantages:
  Inability to monitor crystals in the process of their growth.
 The need to expensive autoclave.
 Safety issues during the reaction process.

Applications:

 Various kind of Nano structures can be center sized of through solvothermal approaches
including medal oxides carbonaceous Nano Structures and etc.,
 This method can also be used produce zeolite, nano wires, carbon nanotubes.

B)Hydrothermal synthesis:

 Hydrothermal synthesis is carried out in an autoclave under autogenous (high) pressure

and below the supercritical temperature of water (374 °C).
 These conditions are favorable for the crystallization of products.
 pH of the medium tobe maintained, pH is generally made alkaline to increase the
solubility of the reactants.
 Example-Synthesis of ZnO nanoparticles
 This process is carried out in teflon lined sealed stainless steel autoclave at the
temperature range of 100 - 200 °C for 6 - 12 hrs under autogenous pressure.
 The stock solution of Zn(CH₃COO)₂ . H₂O (0.1M) was prepared in 50ml methanol
under stirring.
 25 ml of NaOH(0.2-0.5M) solution prepared in methanol was added to maintain pH (8-
11), Finally at the end of the reaction white ZnO nano particles are formed.
  Metal oxides, Carbon nanotubes etc. can be prepared this way.

Advantages

 Solvent used is water.

 Rate of the reaction is much faster at high temperature and pressure.
 Ability to synthesize large crystals of high quality.
 Reagents and solvents can be regenerated.
 Used to prepare nanomaterials of different morphology (powder, rod, wire, tube, single
crystals and nanocrystals).

Disadvantages:

 High cost of equipment.

 Sometimes, it is difficult to predict the morphology of the product.

6. Briefly explain the chemical vapour deposition (CVD) method and laser ablation
techniques for the synthesis of nanomaterials
Chemical Vapour Deposition (CVD) :
 This process involves conversion of gaseous molecules into solid nanomaterials in the
form of tubes, wires or thin films.
 First the solid materials are converted into gaseous molecules and then deposited as
nanomaterials.

 The CVD reactor consists of a higher temperature vacuum furnace maintained at inert
atmosphere.
 The solid substrate containing catalyst like nickel, cobalt, iron supported on a substrate
material like, silica, quarts is kept inside the furnace.
 The hydrocarbons such as ethylene, acetylene and nitrogen cylinders are connected to the
furnace.
 Carbon atoms, produced by the decomposition at 1000°C, condense on the cooler surface
of the catalyst.
 As this process is continuous, CNT is produced continuously.
1. Hot-wall CVD

Hot wall CVD reactors are usually tubular in form. Heating is done by surrounding the reactor
with resistance elements.

2. Cold-wall CVD

In cold-wall CVD reactors, substrates are directly heated inductively while chamber walls are air
(or) water cooled.

Advantages of CVD

1. Nanomaterials, produced by this method, are highly pure.

2. It is economical.

3. Nanomaterials, produced by this method, are defect free.

4. As it is simple experiment, mass production in industry can be done without major difficulties.

Laser ablation

 In laser ablation technique, high-power laser pulse is used to evaporate the material from
the target.
 The stoichiometry of the material is protected in the interaction.
 The total mass ablated from the target per laser pulse is referred to as the ablation rate.
  This method involves vapourisation of target material containing small amount of
catalyst (nickel or cobalt) by passing an intense pulsed laser beam at a higher temperature
to about 120°C in a quartz tube reactor.
 Simultaneously, an inert gas such as argon, helium is allowed to pass into the reactor to
sweep the evaporated particles from the furnace to the colder collector.

Uses:

1. Nanotubes having a diameter of 10 to 20 nm and 100 µm can be produced by this method.

2. Ceramic particles and coating can be produced.

3. Other materials like silicon, carbon can also be converted into nanoparticles by this method.

Advantages of laser ablation:

1. It is very easy to operate.

2. The amount of heat required is less.

3. It is eco-friendly method because no solvent is used.

4. The product, obtained by this method, is stable.

5. This process is economical.

7. Define CNTs. Explain any two methods to synthesize CNTs and list four applications.

Carbon Nanotubes (CNTs)

Carbon Nanotubes (CNTs) are cylindrical nanostructures made of rolled-up sheets of graphene.
They exhibit unique mechanical, electrical, and thermal properties. CNTs can be classified into:

1. Single-Walled Carbon Nanotubes (SWCNTs): One layer of graphene.

2. Multi-Walled Carbon Nanotubes (MWCNTs): Multiple layers of graphene.

Synthesis Methods of CNTs

1. Electric Arc Discharge method or Plasma Arcing

 In this method, two graphite electrodes are installed, and the distance between the two
rod tips is usually in the range of 1–2 mm.
 The anode and cathode are made of pure graphite.
 The anode is drilled, and the hole is filled with a mixture of metal catalyst powder like
iron, cobalt, nickel or yttrium and graphite powder.
 Then the chamber is filled with a rarefied ambient gas like Helium or Argon using a
diffusion pump.
 The electrical discharge that results brings the temperature up to 6000oC. This
temperature is hot enough for the carbon contained in the graphite to sublimate.
 During sublimation, the pressure increases, thus ejecting carbon atoms from the anode
and forming a plasma.
 These atoms move towards the cathode forming a nanotube deposit.
 If the catalyst metal powders are used, then single wall carbon nanotubes are the
dominant product.
 In the absence of such catalysts, the formation of multi wall carbon nanotubes are
favoured.
 During the arc-discharge, web-like structures are formed around the cooler parts of the
electrodes. Within these structures, bundles of 10-100 single wall carbon nanotubes are
 formed. This particular method is normally inefficient giving only around 25% pure
carbon nanotubes. However, the use of a combined nickel-yttrium catalyst has improved
the efficiency and overall production of single wall carbon nanotubes.

Drawback: Requires high temperature and may contain impurities.

2. Chemical Vapor Deposition (CVD)(Refer Ans.6)

 Hydrocarbon gases (e.g., methane) are decomposed at high temperatures (~700–900°C)

in the presence of a metal catalyst (like Fe, Ni).
 Carbon atoms from the gas deposit on the catalyst, forming CNTs.
 Advantage: Large-scale, low-cost production.

3. Laser Ablation Method)(Refer Ans.6)

 A high-powered laser is used to vaporize a graphite target mixed with a catalyst in a

furnace.
 Carbon vapor condenses to form CNTs.
 Advantage: Produces high-quality CNTs.
 Drawback: Expensive and not suitable for mass production.

Applications of CNTs

1. Electronics: Used in transistors, displays, and sensors.

2. Energy: Enhance efficiency in batteries and fuel cells.
3. Medicine: Drug delivery systems and biosensors.
4. Materials: Strengthen composites in aerospace and automotive industries.

8. Enlist the differences between top-down approach and bottom-up approach.

S.NO TOP- DOWN APPROACH BOTTOM – UP APPROACH

1. Top – down approach refers to slicing or Bottom – up approach refers to the buildup
successive cutting of a bulk material to get of materials from the bottom , i.e atom by
a nano sized particles atom or molecule by molecule.

Atom by atom deposition leads to

formation of self – assembly of atoms/
molecules and clusters.

These clusters come together to form self –

 assembled monolayers on the surface of the
substrate.

2. The starting material is solid state The starting material is either gaseous state
or liquid state of matter

3. Physical processing method: Physical and Chemical processing method:

Mechanical methods: cutting, etching, Physical technique:

grinding, Ball milling
Physical vapour Deposition(PVD): involves
Lithographic techniques: Photo condensation of vapour
lithography, Electron bean phase species
lithography
-Evaporation

-Sputtering

-Plasma Arcing

-Laser ablation

Chemical techniques:

Chemical Vapour Deposition(CVD):

involves the deposition of vapour phase of
reaction species

Self-assembled monolayer:
Electrolytic deposition, Sol-gel method ,
pyrolysis.

4. Advantages: Advantages:
✓ Large scale production: ✓ Ultrafine nanoparticles, nanoshells,
deposition over a large substrate is nanotubes can be prepared
possible
✓ Deposition parameters can be controlled
✓ Chemical purification is not required
✓Narrow size distribution is possible(1-
20nm)

✓Chepeast technique
5. Disadvantages Disadvantages

Yields:  Large scale production is difficult

 Broad size distribution (10-  Chemical purification of

1000nm) nanoparticles is required

 Control over deposition parameters

is difficult to achieve.

 Varied particle shapes or geometry

Impurities: stresses, defects and

imperfections get introduced

✓ Expensive technique

6. Limitations: Limitations:
Limited precision at the nanoscale; Challenging to scale up for mass
difficult for very small structures. production; can be time – consuming and
complex.

Applications: Applications:
7.
Nanotechnology , nanomedicine ,
Semiconductor industry , large– scale
material science and nanoelectronics.
manufacturing.

Example:
8. Example:
Self – assembly, molecular beam epitaxy,
Lithography , etching , grinding or milling sol – gel synthesis or atomic layer
deposition.
processes.

Part C (15marks)
1. Compare conventional composite with nanocomposites and discuss the different
types of nanocomposite.
Ans:
Definition for Nanocomposite: Nanocomposites are materials that are reinforced with
nanoparticles.

Conventional composite Nanocomposites

Material Comprise larger-scale reinforcing Incorporate nanoscale
Structure materials, such as fibers (glass, carbon) reinforcements (1-100 nm) like
or larger particles, embedded in a nanoparticles, nanotubes, or
matrix material (e.g., polymers, metals, nanoclays within a matrix,
or ceramics). leading to enhanced
interactions at the molecular
level.
Mechanical Mechanical properties (strength, Exhibit superior mechanical
Strength stiffness, toughness) less compared to properties (strength, stiffness,
nanocomposites toughness) compared to
conventional composites due to
the high surface area and
effective load transfer at the
nanoscale.
Thermal Low thermal stability Nanocomposites can offer
Stability improved thermal resistance
and stability, which is
beneficial in high-temperature
applications.
Functionality New functionalities may not be Nanocomposites can introduce
achievable with conventional new functionalities, such as
composites. electrical conductivity or
improved UV resistance.
Fabrication Conventional composites typically use Nanocomposites may require
Techniques techniques like hand lay-up, resin more advanced processing
transfer molding, or pultrusion.. methods (e.g., sol-gel,
electrospinning) to ensure
uniform dispersion of
nanoparticles
Cost Conventional composites are generally Nanocomposites can be more
more cost-effective for bulk production. expensive due to the cost of
nanomaterials and the
complexity of their processing.
Application Widely used in industries like Gaining traction in high-
construction, automotive, and aerospace performance applications such
for structural components, insulation, as electronics, advanced
and lightweight structures. coatings, biomedical devices,
and high-efficiency energy
 storage systems.

Nanocomposites can be categorized based on the matrix material and the type of nanoparticles or
nanofillers used. The common types are:

a). Polymer matrix composites:

These consist of a polymer matrix reinforced with nanoscale fillers.
Examples:
Clay Nanocomposites: Incorporating layered silicates (like montmorillonite) into
polymers to improve mechanical properties and barrier performance.
Carbon Nanotube Reinforced Polymers: Enhancing electrical conductivity and strength.
b).Metal matrix composites:
Metals are combined with nanoscale reinforcements to enhance mechanical and thermal
properties.
 Increased hardness, strength and superplasticity;
 Lowered melting point;
 Increased electrical resistivity due to increased disordered grain surfaces;
 Increased miscibility of the non-equilibrium components in alloying and solid
solution;
 Improved magnetic properties such as coercivity, superparamagnetsation,
saturation magnetization and magnetocolatic properties
c).Ceramic matrix composites:
Ceramics are reinforced with nanoscale fillers to enhance toughness and thermal stability.

 Increase in the strength, hardness, and abression by refining particle size

 Enhance ductility, touchness, formability, superplasticity by nanophase
 Change electrical conduction and magnetic properties by increasing the
disordered grain boundry interface

2. Describe any three methods of synthesizing nanomaterials with suitable diagrams.

(Refer Pervious answers)

Synthesis of Nanomaterials

Nanomaterials can be synthesized using various physical and chemical methods. Below are three
key methods commonly employed:

1. Pyrolysis Method

 Principle: Decomposition of a carbon-rich precursor at high temperatures.

 Process:
1. A hydrocarbon gas (e.g., methane, ethylene) is used as a precursor.
 2. The gas is introduced into a furnace at high temperatures.
3. The hydrocarbon decomposes, and carbon atoms nucleate on metal catalysts,
forming nanomaterials (e.g., nanotubes).

 Application: Used for synthesizing carbon nanotubes..

2. Arc Discharge Method

 Principle: Vaporization of carbon atoms using an electric arc.

 Process:
1. Two graphite electrodes are placed in an inert gas atmosphere (argon or helium).
2. A high current is passed through the electrodes, creating a plasma arc.
3. Carbon vapor condenses, forming nanomaterials like CNTs on the cathode.
4. This method can also produce fullerenes and graphene.

 Drawback: The resulting product may contain impurities.

3. Chemical Vapor Deposition (CVD)

 Principle: Formation of nanomaterials through the decomposition of gaseous reactants on

a catalyst.
 Process:
1. A gaseous hydrocarbon (e.g., acetylene, methane) is introduced into a high-
temperature reactor.
2. A metal catalyst (e.g., nickel, iron) is placed on the substrate inside the reactor.
3. The carbon atoms from the gas deposit on the catalyst, forming nanotubes or
nanowires.

 Advantages:

o Suitable for large-scale production.

o Produces high-quality nanomaterials.