1. DR. R.K. KHANDAL
DIRECTOR
TECHNOLOGICAL CHALLENGES FOR
MATERIALS OF 21st
CENTURY
SHRIRAM INSTITUTE FOR INDUSTRIAL RESEARCH
19, UNIVERSITY ROAD, DELHI - 110007
Email : sridlhi@vsnl.com Website : www.shriraminstitute.org
2. OUTLINE
Classification of materials
Properties of materials
Bulk Materials
Internal Structure
Nanomaterials
Structure: Size, Shape & Surface area
Designing nanomaterials
Approaches
Mechanical Parameters
Ideal strength
Quantum effects
Photocatalytic materials
Magnetic materials
Optical materials
Adhesive materials
Approaches so far
Challenges
Path forward
Defects
3. Classification of Materials (Type & Structure)
Composites
Ceramics
Polymeric
Crystalline
Polycrystalline
Amorphous
Metallic
Electronic
Biomaterials
Nanomaterials
Nanomaterials include all classes of materials at the nanoscale
Nanomaterials are categorized as 0-D (nanoparticles),1-D
(nanowires, nanotubes, nanorods), 2-D (nanofilms,
nanocoatings), 3-D (bulk)
4. 101Properties of Materials : Critical Factors (Bulk Vs Nano)
DefectsDefects
+
Mechanical
Optical
Thermal
Magnetic
At the nanoscale, interactions with heat ,light, stress, electrical
field & magnetic field give rise to interesting & novel properties
A thorough understanding of the nature of interactions at the
bulk & nano levels are essential for designing nanomaterials
InternalInternal
StructureStructure
Bulk
(Macro & micro) Nano
SizeSize
ShapeShape
SurfaceSurface
areaarea
+
+
5. Structure of Bulk Materials : Internal Structure
Atomic Structure
Ionic Bonding e.g. NaCl
Covalent Bonding e.g. CH4, C2H6
Metallic Bonding
Strong
High melting, brittleness & poor
electrical conductivity
Aggregate of positively charged cores
surrounded by a sea of electrons
Path of electron is completely random
Good conductors, highly ductile
Weak
Poor ductility & electrical conductivity
Brittle & insulators
Shared electrons
6. FCC
Rock salt
Cesium Chloride
Zinc blende
BCC
HCP
E.g. Cu, Ag, Au, Ni, Al,Fe
E.g. Fe, W, Cr
E.g. Zn, Co, Ti, Fe
E.g. MgO, MnS, LiF, FeO
E.g. ZnTe, SiC
SimpleComplex
Some elements exists in more than one crystalline state eg: Iron
Fe BCC750 0
C
∇
FCC
RT
125 kbar
HCP
E.g. CsBr, CsI
Crystal Structure
Structure of Bulk Materials : Internal Structure
7. Molecular structure
Repetition of monomer Homo-polymers & Co-polymers
Linear, Branched, Cross-linked & Network structures
Spaghetti like structure
Presence of many Vander-Waals bonds
Examples : PE, PS, Nylon, etc.
Random Co-polymer
Alternating Co-polymer
Block Co-polymer
Graft
Co-polymer
Linear polymer
Branched
polymer
Crosslinked
polymer
Polymers
Structure of Bulk Materials : Internal Structure
8. Bulk Materials : Defects
Reasons :
Atomic packing problems during processing
Formation of interfaces with poor atomic registry
Generation of defects during deformation.
106
104
102
100
10-2
10-4
10-6
10-8
Bulk
defects
Interfacial
defects
Line
defects
Atomic
point defects
Electronic
point defects
Micrometers
Point
Micro
defects
Macro
defects
Planar
Linear
Volume
Types Classification
Vacancy
Self interstitial
Schottky defects
Frenkel defects
Ductility of metals
Brittleness of ceramics
Formation of cavities
/bubbles during
casting
Effects :(a)Constructive : C in Fe High strength
0.01% of As in Si in Conductivity of Si by 10,000 times
(b)Destructive: Dislocations Deformation in plastics
9. 0 - D
1 - D Rods
Tubes
Wires
2 - D
Basic Geometry Large Scale Forms
Nanocomposite
thick film
Nanocomposite
thick film
Thin film on
substrate Bulk
Nanocomposites
Scope: Ability to design materials with tunable optical, electrical,
magnetic, thermal & mechanical properties
(Dimension at micro or macro scale)
d 100 nm
d 100 nm
Structure of Nanomaterials: Size and Shape
10. Structure Nanomaterials : Shape and Surface area
Different shapes
Sphere
Cylinder
Cube
Critical Dimension (nm)
SurfacetoVol.ratio(nm-1
)
0
0.5
1.0
1.5
2.0
3.0
3.5
20 40 60 80 100
2.5
Sphere : S : V = 3 : r
e.g.: Shape
Volume remains
constant
(10 µm) (10nm)
523 nm3
V (10 µ m)
V (10nm)
5.23 x 1011
523
= = 1x109
particles
One single particle of 10 microns can generate 1 billion nanosized
particles of 10nm; increase in surface area by a factor of 1000
Surface area
Size
Volume 5.23 x 1011
nm3
Number of particles
3.14x108
nm2
314 nm2
Scope : Imparts extraordinary properties to various day-to-day
products like self cleaning windows, anti-wrinkle textiles, etc.
A
V
=
4πr2
4πr3
/3
2πrh
πr2
h
6l 2
l 3
A
V
=
A
V
=Cylinder : S : V = 2 : r
Cube : S : V = 6 : l
Sphere
Distinct
surface to
volume
ratios
12. Designing Nanomaterials : Approaches
Metal
Ceramic
Polymer
Matrix Reinforcing phase
Inorganic
Metals & inorganic
Metals
Examples
Carbides, borides,
nitrides, oxides, etc.
SiC, Zr, Fe, W, Mb,
Ni, Cu, Co, etc.
C nanotubes,
alumina, silica, etc.
Nanocomposites have tremendous scope in all areas of
science & technology.
20. Nano materials
101
Ti alloys
Brass
Mild steel
Al alloys
Copper
Lead
PE, PA
PP, ABS
PS, PET
PVC
Alumina
Zirconia
Glass
Concrete
Bricks
Metals Polymers Ceramics
Ideal Strength
Ideal Strength
To make materials stronger than this is a huge Challenge!
YieldStrength(σy)/Young’sModulus(E)
10-4
10-3
10-2
10-1
Bulk materials fall short of the ideal values in every aspect;
mechanical, optical, electronic, magnetic, thermal, etc.
Nanostructure, nanolayers & amorphous materials are strongest
22. Designing Nanomaterials : Quantum Effects
Conduction band
Vacant state
Conduction band
Vacant state
Conduction band
Vacant state
Valence band
Occupied state Valence band
Occupied state
Valence band
Occupied state
Energy
Conductor
(Metals)
Insulator
(Ceramics)
Semi-conductor
(Silicon)
No band gap Large band gap Small band gap
Bulk level: Atomic energy levels spread out into energy bands;
transfer of electrons from one level to the other is not restricted.
Nano level: Free movement of electrons is restricted due to
confinement of electrons.
At the nano level:
Quantum effects due to confinement of e-
become significant
Energy
Energy
23. Designing Nanomaterials : Quantum Effects
En = Electrons are fully confined
According to quantum mechanics, electron exists inside a deep
potential well from which it cannot escape and is confined by the
dimensions of the nanostructures
Smaller dimension leads to wider separation of energy levels
By spatial confinement of electrons, band gap of a material can be
shifted towards higher frequency
π2
h2
2mL2
nx
2
+ ny
2
+ nz
2
0 - D
En =
π2
h2
2mL2
nx
2
+ ny
2 1 - D
En =
π2
h2
2mL2
nx
2
2 - D
Electrons confinement in two
dimensions
Electrons delocalization in
one dimensions
Electrons confinement in one
dimensions
Electrons delocalization in
two dimensions
h ≡ h/2π ; h = Planck’s constant; m = Mass of e-
; L = Width (Confinement)
Implications
Quantum well
Quantum
wire
Quantum dot
25. Materials with novel approach: Catalytic activity for industrial
effluent treatment.
6.3 eV 3.15 eV 1.58 eV
U.V
200 nm 400 nm 800 nm
Visible
TiO2
ZnO
CdS
WO3
Band gap
Energy
EMS(λ)
TiO2 = 3.20 eV
ZnO = 3.35 eV
WO3 = 2.80 eV
CdS = 2.42 eV
Semiconductors are the most ideal and preferred materials.
Challenge : Maneuvering band gap: Make it sensitive to visible light.
Designing Nanomaterials : Photocatalytic Materials
27. Isolated
nanoparticles
Nano particles
Ultrafine Nanoparticles core
shell morphology in the matrixSmall magnetic
nanoparticles
embedded in a
chemically dissimilar
matrixSmall particles
dispersed in
nanocrystalline matrix
Magnetic nanoparticles
with polymer coating
Metal-matrix nanocomposites are useful for magnetic applications
such as magnetic recordings
Consists of hard magnetic nanoparticles (Nd2Fe14BFm2Fe17N3)
dispersed in a soft nanocrystalline phase (Ferrite, Fe3Pt)
< 1 nm: Non-magnetic
~ 1-10 nm:Super-paramagnetic
>10 nm: Ferromagnetic
E.g. Mn,Co,Fe & Ni
3M2O3.5Fe2O3
Ni0.5Zn0.4Cu0.1Fe2O3
Designing Nanomaterials : Magnetic Materials
28. In the absence of a magnetic field, magnetic interaction
results in spin alignment
When a magnetic field is applied in the opposite direction,
only the soft phase is able to reverse the magnetization.
When the magnetic field is reversed, magnetism is again
reversed in the soft phase
When the applied magnetic field is high enough to reverse
the spins in the hard phase; soft phase does not reverse
the magnetization
High remenance & high magnetic energy (200 kJ/m3
)
Ability to maximize the soft phase content to enhance
saturation magnetization
Approach: Mechanical alloying of two phases
Designing Nanomaterials : Magnetic Materials
This effect is dependent on the size of particles, volume
fraction & distribution of each phase
Hard & Soft phases interact magnetically & for best effects, the two
phases must be at the nanoscale
30. η =√µrεr
Most promising area of application : Metamaterials
Size, shape & composition of embedded nanoparticles influence the
interactions with light, heat ,sound, waves, etc.
1
2
1
2
+ve R.I.
-ve R.I.
Refractive Index
η =√µrεr
µr: Permeability to magnetic field
εr: Permeability to electric field
• µr, εr= -ve
• Induced phenomena
µr, εr= +ve
Natural phenomena
Designing Nanomaterials : Optical Materials
31. Nano pillars Inhomogeneity
Challenge:
Selection of material
Creation of different surface
Reflection
Transmission
Refraction
Non-uniform surface
Camouflaging
Designing Nanomaterials : Optical Materials
32. The play of light on a butterfly’s wings has inspired designing of
novel photonic materials for solar cells, photovoltaics,
camouflaging, optical fibers and military applications.
Invisibility cloak
Color play
Tailor-making of
refractive index
and dielectric
constant
Camouflaging
Designing Nanomaterials : Optical Materials
34. The ability of a Gecko to scamper up walls has been a very big
inspiration for designing a number of adhesives; Useful for the
lithography industry where nanosurfaces have been patterned
after a gecko’s foot soles.
Clinging ability of Gecko
Intermolecular forces between the
paw & the surface Nano-pillars
~ to Gecko
paw hair
Designing Nanomaterials : Adhesive Materials
35. Inert gas
condensation
Evaporation
colloidal methods
Physical or
chemical vapour
deposition (PVD
OR CVD)
Extrusion,
cryomilling &
sintering
Directional growth
from catalyst dots
Templating
Lithographic
method
Incorporation of
Nanotubes and rods
into polymer or metal
matrices
Beating (gold foil)
Electrodeposition
PVD,CVD
Self-assembled
films
Electrodeposition
Physical vapor
deposition Chemical
vapor deposition
(1) PVD
(2) CVD
(3) Electrodeposition
1-D
2Dimension
innanoscale
-D
1
imension
in
nanoscale
0-D
All3
Dimensionin
nanoscale
Dimensionality
Class 1
Discrete objects
Class 2
Surface featured
Class 3
Bulk structures
Designing Nanomaterials : Approaches So Far
36. Stability ; AgglomerationStability ; Agglomeration
Yield ; Scale-upYield ; Scale-up
SynthesisSynthesis
AssemblyAssembly
ApplicationApplication
Designing Nanomaterials: Challenges
Isolated ; DiscreteIsolated ; Discrete
Hybrid ; DispersionHybrid ; Dispersion
MechanicalMechanical OpticalOptical
ElectricalElectrical MagneticMagnetic
ThermalThermal
Utilization of single nanostructure for processing electrical,
optical or thermal signals.
Assembling nanostructures for electronic, chemical & other
applications.
37. Path Forward
Development of nanotechnology & nanomaterials for:Development of nanotechnology & nanomaterials for:
Storing energy rich gasesStoring energy rich gases
Fuel cellsFuel cells
Solar cellsSolar cells
Photovoltaic textilesPhotovoltaic textiles
Self cleaning, Anti-microbial & other surface properties:Self cleaning, Anti-microbial & other surface properties:
Nano paintsNano paints
Nano sealantsNano sealants
Smart materialsSmart materials
Only nanomaterials have made possible the development ofOnly nanomaterials have made possible the development of
futuristic materials with extraordinary propertiesfuturistic materials with extraordinary properties
