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. 2021 May:73:105493.
doi: 10.1016/j.ultsonch.2021.105493. Epub 2021 Feb 10.

Acoustic cavitation at low gas pressures in PZT-based ultrasonic systems

Joydip Mondal  1 , Wu Li  2 , Amgad R Rezk  3 , Leslie Y Yeo  3 , Rajaram Lakkaraju  4 , Parthasarathi Ghosh  5 , Muthupandian Ashokkumar  6
Affiliations

Acoustic cavitation at low gas pressures in PZT-based ultrasonic systems

Joydip Mondal et al. Ultrason Sonochem. 2021 May.

Abstract

The generation of cavitation-free radicals through evanescent electric field and bulk-streaming was reported when micro-volumes of a liquid were subjected to 10 MHz surface acoustic waves (SAW) on a piezoelectric substrate [Rezk et al., J. Phys. Chem. Lett. 2020, 11, 4655-4661; Rezk et al., Adv. Sci. 2021, 8, 2001983]. In the current study, we have tested a similar hypothesis with PZT-based ultrasonic units (760 kHz and 2 MHz) with varying dissolved gas concentrations, by sonochemiluminescence measurement and iodide dosimetry, to correlate radical generation with dissolved gas concentrations. The dissolved gas concentration was adjusted by controlling the over-head gas pressure. Our study reveals that there is a strong correlation between sonochemical activity and dissolved gas concentration, with negligible sonochemical activity at near-vacuum conditions. We therefore conclude that radical generation is dominated by acoustic cavitation in conventional PZT-based ultrasonic reactors, regardless of the excitation frequency.

Keywords: Acoustic cavitation; Cavitation bubbles; Cavitation-free radical generation; Sonochemical activity.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Fig. 1
Fig. 1
Schematic showing the experimental setup using A) a fabricated flask with stopper; B) degassing setup providing different overhead gas pressures; C) measurement of sonochemical activity by 2 methods. The arrows indicate where the 4 types of solution with different gas concentrations (a1: 101325 Pa, a2: 2000 Pa, a3: 33 Pa, a4: 3 Pa) were acquired.
Fig. 2
Fig. 2
A) SCL signal and 2B) radical yield at near vacuum conditions (3 Pa) with volume of PZT cell ~50 mL at a frequency of 760 kHz. SCL signals are normalized; Error bars are shown on the top of each bar with a circle marker.
Fig. 3
Fig. 3
SCL intensity observed at different dissolved gas pressures (in Pa) in sonicating luminol solution.
Fig. 4
Fig. 4
Radical yield measurements (μM/min) for different dissolved gas pressures on sonicating water at different frequencies.
See this image and copyright information in PMC

References

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