a. kesavasami, k. khinchi, a. goyal, n. roy and r. nagarajan dept of chemical engineering iit madras...
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A. Kesavasami, K. Khinchi, A. Goyal, N. Roy and R. Nagarajan
Dept of Chemical EngineeringIIT Madras
CAV 2012, Aug 13-16, 2012, Singapore
Sono-Synthesis and Dispersion of Nano-Particles: Experiments & Simulation
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WHAT IS SONO-TECHNOLOGY?
Intensification of bulk-fluid and surface/ interfacial processes by combined
action of cavitation (bubble implosion) and acoustic streaming
(high-velocity shearing)
2
micron-size bubbles
Cavitation Bubble
Acoustic Streaming
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SONO- FRAGMENTATION(SIZE REDUCTION)
4
Particles
Bubble
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Particles
BubbleBubble Collapse due to Implosion
Particle Fragments due to
a) Violent Bubble collapse
b) Inter-particle attrition
SONO- FRAGMENTATION(SIZE REDUCTION)
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Particles
BubbleBubble Collapse due to Implosion
Particle Fragments due to
a) Violent Bubble collapse
b) Inter-particle attrition
Fragmented Particle
SONO- FRAGMENTATION(SIZE REDUCTION)
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STATE-OF-THE -ART ULTRASONIC FACILITY
7
58 kHz, 500 W power Sonicator
( Tank Type)
20 kHz, 1000 W power Sonicator
( Probe Type)
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ANALYZERS USED
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20 kHz_ 500 W
30 minutes
PARTICLE SIZE BEFORE AND AFTERSONO-FRAGMENTATION
0.01 0.1 1 10 100 1000 100000
20
40
60
80
100
Particle size (m)
% P
assi
ng
0
2
4
6
8
10
% C
han
nel
10 100 10000
20
40
60
80
100
Particle Size(m)
% P
assi
ng
0
4
8
12
16
20
% C
han
nel
9
Feed Particle Size (74-80 microns)
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EFFECT OF FREQUENCY ON SONO-FRAGMENTATION
10 20 30 40 50 600.028
0.029
0.030
0.031
0.032
((d
pIn
itia
l - d
pF
inal)/
dp
Init
ial)/
S.T
Expt. Cond. : 20 kHz, 500 W, 30 Min
Sonic Frequency (kHz)
10
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EFFECT OF APPLIED ULTRASONIC POWER ON SONO-FRAGMENTATION
250 500 750 10000.0315
0.0320
0.0325
0.0330
((d
pIn
itia
l - d
pF
inal)/
dp
Init
ial)/
S.T
Expt. Cond. : 20 kHz, 500 W, 30 Min
Sonic Power (Watts)
11
Sonic power plays a key role in intensifying the cavitation bubble movement, bubble collapse, and inter-particle attrition.
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20 kHz, 1000 W, Sono-fragmented WFA
nm dimensions confirmed.
20 nm20 nm 5 nm5 nm
12
HR TEM PICTURES
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Simulation of Sono-Fragmentation
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MODEL VALIDATION WITH MEASURED DATA
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DISPERSION OF NANOPARTICLES IN SUSPENSION
Cohesive tendency
Hydrophobic particles in water attract
Hydrophilic particles in water repelHence, surfactant coating of nanoparticles in
suspensions helps keep them apart
Dynamic behaviorMean size increases with time
Total # decreases with time
Population balance modeling required
Dispersion just prior to processing is generally required 17
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COHESIVE FORCE AS A FUNCTION OF INTER-PARTICLE DISTANCE IN A COLLOIDAL
SUSPENSION
18
From Drelich et al., 2006
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From rti.edu19
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High-Frequency Sono-Blending of Particles in Suspension: Beaker Decantation Trials
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30 minutes Sono-fragmented Al(OH)3
(Prior to Blending)
21
150
300
450
600
20 58
Frequency (kHz)
Tu
rbid
ity
(N
TU
)
Level 1 Level 2
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20kHz sono-fragmentedfollowed by 58 kHz Blending
22
50
450
850
30 60 90 120
Sono- Blending Time (Minutes)
Tu
rbid
ity
(N
TU
)
Level 1 Level 2
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20kHz sono-fragmentedfollowed by 132 kHz Blending
23
50
450
850
1250
1650
15 30 45 60Sono-Blending Time (Minutes)
Tu
rbid
ity
(N
TU
)
Level 1 Level 2
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Optimum Sono-Blending Timeas a function of frequency
24
15
20
25
30
35
40
20/33 20/58 20/132
Ultrasonic Frequency in kHz
Op
tim
un
So
no
-Ble
nd
ing
Tim
e
(Min
ute
s)
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Effect of pH on Dispersion Stability
Nano-ZnO suspensions in pure water, ascending order of pH: 3, 5, 7, 9, 11, 13 (dispersed using 40 kHz ultrasonication)
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Variation of Absorbance of Supernatant with Time of Centrifuge (4000 rpm)
0 2 4 6 8 10 12
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
pH 3 pH 5 pH 7
pH 9 pH 11 pH 13
Time (minutes)
Redu
ced
Abso
rban
ce
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Conclusions
• Sono-fragmentation is a promising top-down method for nano-particle synthesis– Low-frequency, high-cavitation fields work best– High purity, ease of scale-up– Can be simulated via population balance techniques
• Sono-dispersion is an effective method for preparing nano-particle suspensions– Higher frequencies are optimal– Solution chemistry will play a role– Long-term stability to be verified
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Acknowledgment
• Crest Ultrasonics Corporation (Trenton, NJ, USA) provided the sono-processing equipment used in this study.