Transcript Slide 1

Scientific and Technological Challenges in the
Production of Nanostructured Ceramics
Pradip
Tata Research Development & Design Centre, Pune, India
[email protected]
Bangalore Nano 2007
1
“Research to Reality” in Nanotechnology
However, today there is a nanotechnology center in practically every
institution in the country, and worldwide research in nanomaterials is
booming………………….There certainly is a lot of hype about
nanotechnology. Except for the tremendous advances in the
semiconductor chip industry, which in any case were already there
before the launch of the nanotechnology initiative, currently there are
not many innovations in the market place based on nanotechnology. The
projections about the potential market being as large as $1 trillion sounds
really exaggerated.
From an engineering point of view, before this field can really be called a
technology, much more needs to be done with respect to the reliability,
reproducibility, standardization, productivity and engineering scale-up so
that laboratory claims or successes can actually be scaled-up and
realized in practice. Certainly major effort should be undertaken to
understand the environmental, health and safety impacts of engineered
nanoparticles.
2
Contd…….
Producing nanotubes, nanorods, hollow nanoparticles, core and shell
nanoparticles are certainly results of innovative chemistry and physics
in the laboratory but to claim this as a technology is not correct. One
sees excellent TEM/SEM photographs of these particles but to produce
them reproducibly even at the kg scale currently is not an easy task. It
is the involvement of process engineers and the applications of
process engineering tools which will take this to the next stage.
Pioneering work done by mineral processing engineers to understand
the modeling and scale-up issues related to particle processing
needs to be emulated by those working in the nano area. One problem
is that not very many engineers are currently associated with this field,
but chemical engineers appear to be realizing the opportunities this
field offers.
DW Fuerstenau, AIChE Particle Technology
Forum - Life Time Achievement Award, 2006
3
Research to Reality - NNI
 From investigation of single phenomena and creating single
nano-components to complex, active nanostructures
 From scientific discovery to technological innovation in
advanced materials, nanostructured chemicals, electronics
and pharma
 Expanding to new areas of relevance such as energy, food
and agriculture, nanomedicine and engineering simulations
from the nanoscale (multi-scale modeling)
 Accelerating development
Rocco, 2007
4
Large Scale Production of Carbon Nanotubes
 Fluidized Bed Reactor for production of CNT’s in tons per
day (Tsinghua University, China) – Prof. Wei Fei’s group
 CVD method to produce high purity single-walled carbon
nanotubes (SWNTs) and multi-walled carbon nanotubes
(MWNTs) with various diameters and narrow diameter
distribution; Facilities to produce 1.5kg high purity
SWNTs per day and 20kg MWNTs (10-20nm in diameter)
per day. The production facilities can be scaled up easily to
produce MWNTs with purity more than 98wt% max. [The
Chengdu Institute of Organic Chemistry, Chinese Academy
of Sciences: R&D Centre for Carbon Nanotubes]
5
Nanomaterials Research Program at TRDDC
Aerosol Flame
Reactors
Titania
Carbon Black
Silica
Drug Delivery
Coatings
Metals/Metal Oxides
Semiconductors
Nanofluids
Engine Coolants
Transmission Fluids
Population
Balance
Modeling
Nanogels
Microemulsions
Engineered
Nanostructured
Components
Microfluidics
PolymerNanocomposites
Transparent Alumina
Advanced Ceramics
Particulate
Processing
Rheology
Surface Science
Molecular
Modeling
Ink-jet Printing
Rapid Prototyping
Computational
Fluid
Dynamics
Linkages with Appropriate Industrial Partners
6
Fabrication of Nanostructured Ceramics Components
 Full consolidation of nano-powders into fully dense, defect free large
engineering components while retaining nanostructures
 Challenge in consolidation of nano-crystalline particles: grain coarsening ;
loss of desired nano structure during processing & fabrication
 Fast sintering/densification inversely proportional to pore size.
Densification rate is dictated by the instantaneous pore size not the initial
pore size and hence pores should remain small throughout.
 Close control of pore size and pore size distribution (narrow) is the key to
restrict grain growth and thus retain nano structures
Joanna Groza, Int. J. Powder Metallurgy, Vol. 35(7), 1999, pp 59-66]
7
 Non Conventional Sintering
To enhance densification & prevent grains growth
 Hot Pressing
 Hot Isostatic Pressing (HIP)
 Sintering Forging
 Hot Extrusion
 Ultra high Pressure Sintering
 Microwave Sintering
 Field Assisted Sintering Techniques (FAST)
– Pulsed current discharge and resistance heating also known as
» Plasma activated sintering (PAS)
» Spark Plasma Sintering
» Pulse electro-discharge consolidation
– Dynamic Magnetic Compaction (DMC) (short high pressure
pulses)
 Shockwave Consolidation
8
Colloidal Processing of Nanoparticles and
Production of Sintered Nanostructured Ceramics
Nanoparticles
Suspensions
Dispersion
Consolidation
Design of Dispersants
Slip/tape/gel casting/
pressure filtration
Dispersed Conc. Slurry
Green Compact
Sintering
Dense
Homogeneous compacts
Challenges: Close control of pore size distribution
Restrict grain growth
Retain nano-structures
9
Design of Sintering Time –
Temperature Cycles
Rational Design of Additives
Experiments
Molecular Modeling

Dispersion/flocculation

Atomistic

Rheology

Ab- initio/DFT

Flotation

Molecular Dynamics (MD)

Adsorption

Dissipative Particle Dynamics (DPD)
• Self assembly at interfaces
•
Colloidal stability
•
Wettability
10
Molecular Modeling Methods
Quantum Mechanics
 Ab initio (HF, MP2)
 DFT
 Semi-empirical
EHMO, CNDO,
MINDO, MNDO,
ZINDO
Force Field
 MM2
 AMBER
 OPLS
 UFF
 Drieding
 COMPASS
11
Molecular Dynamics
 NVE
 NVT
Dispersants for Tape Casting of Barium Titanate
Oleic Acid
OLA
Octanoic Acid
OCA
(CH2)7
CH3
(CH2)5
CH3
Menhaden Fish Oil
COOH
COOH
CH
COO
(CH2)10
5
O
Emphos PS-21A
(CH2)7
CH
(CH2)6
CH3
Polyhydroxy Stearic Acid PHS
CH
CH
2
(CH )
2 18
CH
3
CH2
(CH )
2 18
CH
3
P
EPS
HO
MFO
CH3
(CH2)7
CH
CH
(CH2)7
COO
CH2
CH3
(CH2)7
CH
CH
(CH2)7
COO
CH
CH3
(CH2)7
CH
CH
(CH2)7
COO
CH2
CH3
Zonyl-A
Alkazine – O
ZNL
AIME
CH3
CH3
(CH2)3
(CH2)7
CH
CH
C
CH3
CH3
CH
(O
OH
N
(CH2)7
N
12
(CH2)2 )9
CH2
CH2
OH
Molecular Dynamics Simulation
105
BaTiO3 in Decane
BaTiO3(001) /Glycerol
trioleate /Acetone
Viscosity (mPas)
104
OCA (0.2)
103
102
PHS (0.2)
101
MD Simulation
300 °K and 300 ps
Expt
OLA (0.3)
Ref.: Bergstrom et.al. (1997), J. Am. Ceram. Soc., 80, pp. 291
Interaction energy (-kcal/mol)
100
10-1
100
101
102
Shear rate (1/s)
200
MD Simulations
(Hexane, 300 K, 300 ps)
150
Theory
100
50
0
PHS
Data from: Bergstrom et.al. (1997) J. Am. Ceram. Soc., 80, pp. 291
103
OLA
OCA
Dispersant
Pradip et al., Ferroelectrics, 306, 2004, 195-208
13
Population Balance Modeling of Sintering
Prediction of Microstructure Evolution during Sintering
 Extensive research /published literature on idealized systems available
on the mechanisms of sintering but difficult to translate into commercial
solutions
 Need exists for a quantitative approach to optimize sintering cycles
 What kind of green body microstructure is desirable for desired
properties in the final product?
 Is it possible to embed our fundamental mechanistic understanding in a
mathematical representation (model) of commercial sintering process
(size distribution) so as to be able to optimize practical systems
 Population balance paradigm offers such a possibility
14
Sintering Stages
Initial Stage
Rapid interparticle neck growth by diffusion, vapor transport, plastic or
viscous flow
Intermediate Stage
Pores reach equilibrium shape as dictated by interfacial free energy. A
network of grain and pores defines the microstructure whose evolution is
driven by trajectories of pore and grain size distributions. This stage
normally covers the major part of sintering process
Final Stage
Pores may get pinched off and exist in isolation at grain corners or and
within the grains. Abnormal grain growth can occur
15
Population Balance Paradigm
Changes due to convection in physical space
Accumulation Term
H




(v x H ) 
(v y H ) 
(v z H ) 
t
x
y
z
J

j 1

vjH
w j
Continuous changes in
property space

D B 0
Jump changes due to
discrete events
16
An Operational Approach to Intermediate Stage of
Solid State Sintering
In coupled population balance equations for evolution of pore and
grain size spectra, incorporate semi-empirical velocity or
convective terms for:
Pore Shrinkage
Grain Shrinkage and Growth
density
17
Pore Shrinkage and Evolution of
Pore Size Spectra I
• Continuity eqaution
n(r,t)  
dr 
 n( r ,t )   0
t
r 
dt 
• Shrinkage “velocity”
dr
k
 m
dt
r
Q 

k  exp  k 0 

RT 

 n(r,t) is number of pores of radius r at sintering time t.
 m is a floating exponent that need not represent any one particular surface or bulk diffusion
mechanism of shrinkage.
 k is a specific rate constant that follows an Arrhenius type relationship.
 Pore coalescence can be incorporated in the continuity equation.
18
Pore Shrinkage and Evolution of
Pore Size Spectra II
• Solution
n0 ([ r m 1  ( m  1)kt ]1 /( m 1) )
n( r , t ) 
(1  ( m  1)ktr  ( m 1) ) m /( m 1)
• Total pore volume

V (t )  C  n( r, t )r 3dr
0
• Normalized cumulative pore volume distribution

C
3


FV ( r, t ) 
n
(
r
,
t
)
r
dr 

V ( 0) r
19
Grain Growth and Evolution of
Grain Size Spectra I
• Continuity equation
H(r,t) 
 (
t
r
• Growth “velocity”
H(r,t)
dr
)0
dt
 1 1
CG
dr
  

dt 1   (t ) r n  rc r 
Q 

CG  exp  CG 0  G 
RT 

 H(r,t) is number of grains of radius r
 rc is critical radius
 n is a floating exponent that depends on transport mechanism(s)
 CG is a specific rate constant that conforms with an Arrhenius type relationship
  is a coupling parameter. Any alternate plausible coupling relationship can be
employed
20
Model Validation
 Alumina, zirconia powders sintered at different temperatures for varying
times
 Pore size distributions, porosity, grain size distribution as a function of time
and temperature determined for parameter estimation
 Model is adequate to describe the pore shrinkage and grain growth (essence
of sintering kinetics) and hence can be used to simulate sintering for
different conditions.
21
Test of Pore Shrinkage Model I:
Alumina A16 At 1400ºC
1
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S. Manjunath, PC Kapur and Pradip, Materials Chemistry and Physics, 2001, 17-24
22
Test of Pore Shrinkage Model II:
Zirconia Syp 5.2 At 1400ºC
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S. Manjunath, PC Kapur and Pradip, Materials Chemistry and Physics, 2001, 17-24
23
Test of Grain Growth Model II:
Zirconia Syp 5.2, At 1500ºC
1
.
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1
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S. Manjunath, PC Kapur and Pradip, Materials Chemistry and Physics, 2001, 17-24
24
Application: Sintering By Pre-coarsening Hold
I. Alumina At 1450ºC (Lin Data)
Tempratue, oC
1
5
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9
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S. Manjunath, PC Kapur and Pradip, Materials Chemistry and Physics, 2001, 17-24
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Sintering by Pre-coarsening Hold
II. Simulated and Measured Density & Grain Size
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S. Manjunath, PC Kapur and Pradip, Materials Chemistry and Physics, 2001, 17-24
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Sintering by Precoarsening Hold
III. Simulated Alumina Grain Size Distributions
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Simulation of Heating Cycles I
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S. Manjunath, PC Kapur and Pradip, Materials Chemistry and Physics, 2001, 17-24
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Simulation of Heating Cycles II
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S. Manjunath, PC Kapur and Pradip, Materials Chemistry and Physics, 2001, 17-24
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Zirconia Nano Powder Dispersion
d50 (measured by laser
light scattering) 738nm
Agglomerated
received powder
Powder (pH 5)
100
Cumulative vol.%
pH 10
• Reported average Zirconia particle size is
(30 -60nm)
• Received powder is in the form of
aggregates confirmed from TEM and laser
light scattering measurements
PMA (pH 8.5)
80
PMA (pH 8.5), 2hr milling
60
40
20
0
100
1000
Particle size, nm
30
10000
Finer particles
1300oC, 0.5hour,
99.5% Density
Consolidation (300kPa)
Sintering
60
1300oC, 0.5 hour
Frequency (%)
50
40
30
20
10
0
0-20
20-40
40-60
Grain size (nm)
Mamata Pradhan, PC Kapur and Pradip, APT 2007
31
60-80
Densification: Effect of Particle Size
100
Agglomerated powder(738 nm)
Finer powder(70 nm)
o
Temperature (1300 C)
Sintered density (%)
98
96
94
92
90
88
0
0.5
1
Time (Hours)
2
4
With use of a simple technique, starting from 70 nm size particles we
produced fully densified nano structured products with grains < 100nm
Mamata Pradhan, PC Kapur and Pradip, APT 2007
32
Microstructure of Sintered Samples : Effect of Particle Size
Coarser one, Density 94%
Sintered at 1300oC, 1hour
Finer one, Density 99.5%
Sintered at 1300oC, 1hour
33
Concluding Remarks
 Process engineering and scale up issues are critical
 Application driven product development in partnership with
industry
 Innovative use of existing knowledge to meet application
needs
 Innovative business model to convert scientific discoveries
and inventions into commercial succeses
34
Thank You
35