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

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

3

SONO- FRAGMENTATION(SIZE REDUCTION)

4

Particles

Bubble

5

Particles

BubbleBubble Collapse due to Implosion

Particle Fragments due to

a) Violent Bubble collapse

b) Inter-particle attrition

SONO- FRAGMENTATION(SIZE REDUCTION)

6

Particles

BubbleBubble Collapse due to Implosion

Particle Fragments due to

a) Violent Bubble collapse

b) Inter-particle attrition

Fragmented Particle

SONO- FRAGMENTATION(SIZE REDUCTION)

STATE-OF-THE -ART ULTRASONIC FACILITY

7

58 kHz, 500 W power Sonicator

( Tank Type)

20 kHz, 1000 W power Sonicator

( Probe Type)

ANALYZERS USED

8

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)

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

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.

20 kHz, 1000 W, Sono-fragmented WFA

nm dimensions confirmed.

20 nm20 nm 5 nm5 nm

12

HR TEM PICTURES

Simulation of Sono-Fragmentation

MODEL VALIDATION WITH MEASURED DATA

16

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

COHESIVE FORCE AS A FUNCTION OF INTER-PARTICLE DISTANCE IN A COLLOIDAL

SUSPENSION

18

From Drelich et al., 2006

From rti.edu19

High-Frequency Sono-Blending of Particles in Suspension: Beaker Decantation Trials

20

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

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

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

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)

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)

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

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

Acknowledgment

• Crest Ultrasonics Corporation (Trenton, NJ, USA) provided the sono-processing equipment used in this study.