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

https://doi.org/10.1016/j.ultsonch.2021.105493Get rights and content
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Highlights

  • A relation between sonochemical activity and dissolved gas concentration is reported.

  • Acoustic cavitation is responsible for sonochemical activity in PZT based reactors.

  • A relatively higher dissolved gas concentration is needed for sonochemical activity at 2 MHz.

  • Sonochemiluminescence is a highly sensitive technique for the detection of sonochemical activity.

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

Sonochemical activity
Acoustic cavitation
Cavitation-free radical generation
Cavitation bubbles

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