Visualization of Acoustic Cavitation Effects on Existing Crystals 报告人：李洁琼 导师：王静康 教授 2013/03/23

1. Click to add your text Visualization of Acoustic Cavitation Effects on Existing Crystals报告人：李洁琼导师：王静康 教授2013/03/23

2. References

3. Introduction 1 Experimental 2 Results and discussion 3 Conclusions 4 Contents

4. Introduction

5. Distinction • attrition • & • breakage vibration & implosion crystal growth rate Agglomerates An assemblage of particles which are loosely coherent. Aggregates An assemblage of particles rigidly joined together. Acoustic Effects Seed Crystals & Agglomerates Alteration of Crystal Habit & Size Introduction • acoustic cavitation Non-inertial Cavitation(low energetic) microjets Inertial Cavitation(high energetic) high energetic shockwaves buble growth buble collapse shockwave emerge shockwave impact

6. Effect of Cavitation OBD HS methods SEM Introduction 创新点 optical beam deflection measurements high speed imaging Scanning Electron Microscopy analysis

7. B A B1 B2 The first batch was synthesized, using the method described by Nancollas and Reddy: slowly adding 2dm3of a 0.20M CaCl2 (VWR, 100%) solution to 2dm3 0.20M Na2CO3 (Boom, >99.5%) solution at 25 ℃ and dried at 105℃. The freshly precipitated seed crystal batch A and part of batch B, were aged overnight in mother liquor and were subsequently washed with Milli-Q water each day for one week. Afterwards, the washed seed crystals were aged for three weeks before filtering. The other part of batch B was also washed with Milli-Q by carefully replacing the mother liquid by Milli-Q water. After washing the seeds each day for one week, the seeds were stored in Milli-Q water. The second batch was synthesized by adding both solutions simultaneously at 25 ℃. Experimental • Materials Fig. 1. SEM pictures of seed crystals: (A) seed crystals A and (B) seed crystals B.

8. ultrasonic irradiation small thermostatted square glass box 0.05 g calcite seeds 95 mMKCl 1.6 mM CaCl2 1.6 mM NaHCO3 Experimental • Experimental set-up and procedures Fig. 2. Scheme of the experimental set-up consisting of: (1) ultrasonic transducer, (2) high power light, (3) high-speed camera with zoom lens, and (4) glass box. 100mL saturated CaCO3 solution

9. Results and discussion • Bubble structures Fig. 3. Streamer (A) and large clusters (B). Image A is recorded without seed crystals in the liquid, for better distinction of the bubbles from the seeds. Cluster formation always started on the surface of a particle. Part of the ultrasonic source is visible (dark silhouette) at the top of both images. Scale bar is 500 lm (both images).

10. Results and discussion • Disruption of aggregates and deagglomeration Fig. 6. Rupture of type B1 calcite crystal (length: ~41μm), shot at 300,000 fps, scale bar is 53μm. Fig. 4. Images of an oscillating cavitation bubble that nucleated on the surface of a type A calcite crystal. The single crystal fragmentizes as a result of the violent collapse of the bubble. Frame rate: 125,000 fps. Fig. 5. Images of streamer cavitation causing deagglomeration of type B1 calcite crystal (arrow 1). The agglomerate (length: ~49μm) splits up (arrow 3) as a result of the bubble collapse (arrow 2). Frame rate: 125,000 fps; shutter time: 1μs, scale bar is 50μm.

11. Results and discussion • Seed acceleration by bubble expansion and collapse Fig. 7. An example of crystal (B1, length: ~ 36μm, arrow 2) acceleration by bubble (arrow 1) expansion and collapse. Frame rate: 100,000 fps. Scale bar length is 100μm. The cavitation cycle is 23μs which is slightly more than two frames. One frame shows an instant of bubble growth followed by the next frame showing an instant of bubble collapse.

12. Results and discussion • Seed acceleration by bubble expansion and collapse • For each frame the centre position of the particle of interest was measured, the displacement from frame to frame was calculated and multiplied by the frame rate, fps (s-1), the particle velocity (m·s-1)is presented as: • where x (m) is the x-coordinate of the particle of interest and y (m) is the y-coordinate. • In a similar fashion the acceleration (m·s-2)was determined from the acquired velocities:

13. Results and discussion • The drag force on small particles moving through fluids at relatively low speeds, where there is no turbulence, can be described by Stokes’s law. From this law, a general equation of motion can be derived, assuming the liquid velocity to be zero: • The relaxation time is a constant, defined by material and fluid properties: • ρs (kg/m3) - the density of the solid; η (Pa·s) - the liquid viscosity; d (m)- the spherical particle diameter.

14. Results and discussion • Stokes’s law can only be used for Reynolds numbers smaller than 1. At maximum velocity the particle’s Reynolds number is 65 and Newton’s law has to be applied, resulting in the following relaxation time: • where Re (–) is Reynolds number and CD (–) the drag coefficient, described by an empirical relation for 1 < Re < 1000. • In reality the velocity profile will be between Stokes’ law and the outer limit of maximum drag calculated with Newton’s law, defined as the drag window.

15. Results and discussion • Seed acceleration by bubble expansion and collapse not only related to drag Fig. 8. Velocity profile of accelerated crystal B1 from Fig. 7. The velocity at t =0μs corresponds to the velocity between t = 110 and 120μs in Fig. 7. The arrow indicates the large decrease in velocity right after bubble collapse. The dashed line is calculated with Stokes, the dotted line with Newton (outer limit of maximum drag). Calculation based on the (initial) velocity at, (A) t =0s(Re = 65), and (B) t =10 ls(Re = 28).

16. Results and discussion • Effect of cavitation on crystal habit plastic deformation crack growth Griffith cracks Fig. 11. Microjets captured at >250,000 fps. Fig. 9. SEM pictures of voluminous fragments of seeds B1 with large planes of fracture Fig. 10. SEM pictures of damaged calcite seeds. Possible broken aggregates (A, B); circular indentations caused by ultrasound (B, C) and by laser ablation (D) in calcite.

17. Conclusions • Cavitation clusters, evolved from cavitation inception and collapse, caused attrition, disruption of aggregates and deagglomeration. • Crystals that were accelerated by bubble expansion, subsequently experienced a deceleration much stronger than expected from drag forces, upon bubble collapse. • The appearance of voluminous fragments with large planes of fracture indicated that acoustic cavitation can cause the breakage of single crystal structures, and these indentations might be caused by shockwave induced jet impingement. Disadvantage: no direct record of jet impingement on a suspended crystal

18. crystal growth kinetics • concentration in the liquid state • CSD & suspension density Ultrasonic Technology

19. Fig. 12 Experimental setup with ultrasound sensor, controller, and electric stirrer

20. crystal growth kinetics • In liquids, the spread velocity ν of ultrasound waves through a liquid depends on the density ρL of the liquid and its adiabatic compressibility βad: • For determining the crystal growth kinetics, the following four steps were performed: • Measure the saturation point and the nucleation point by the ultrasonic technology. • Determine the correlation between the concentration of a solution and ultrasonic velocity and temperature. • Measure the decrease in supersaturation versus time using ultrasonic techniques. • Calculate the kinetic parameters.

21. crystal growth kinetics • Determination of the kinetic parameters Crystal growth rate: The mass flux:

22. CSD & suspension density • Data Validation • experimental velocity data: • the attenuation: φ - suspension density; βn - experimentally determined parameters

23. CSD & suspension density • Model Identification & Verification

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