Chapter 1
Cavitation and Chemical Reactivity
Abstract The sound is a mechanical vibration which propagates by elasticity
through matter whatever its physical state. On liquid state, an interesting and unique
physical phenomenon was identified at the end of nineteenth century and designated as cavitation, which is the birth, growth and collapse of tiny gas bubbles.
The intensity of bubbles occurrence and of collapse violence is very dependent
on the sound frequency. The most energetic cavitation activity occurs when using
ultrasound frequencies, i.e. above the upper limit of human hearing (18 kHz). The
incident irradiative frequency is therefore of crucial importance leading to effects
on chemical systems of physical and/or chemical nature. Several other operational
parameters do also greatly influence the cavitation process and are here described as
well as most frequent types of ultrasonic devices working either on direct or indirect
mode. ‘Hotspot’ theory and generally admitted reacting zones establishing rules of
sonochemistry are also examined. Finally, some guidelines for good experimental
use of ultrasonic devices are tentatively established by authors based on their own
experience.
1.1 Introduction
To ease the reading of this Brief, necessary rudimental terms and fundamental knowledge on the origin and the nature of effects brought up by ultrasound on chemical
systems will be introduced. Some of the most common ultrasonic devices will be
also introduced. Factors impacting greatly sonochemical activity cannot be omitted, the balance between them allow to reach a maximal acoustic activity ensuring
an optimum cavitation efficiency. These are incident irradiative frequency, working
temperature, amplitude of the acoustic wave, physicochemical characteristics of the
solvent, type of dissolved gases, etc. Some good rules of use, rather based on practical experience than on theoretical rules, will be also tentatively given. Indeed, an
experimental misconduct can lead to false or even anomalous absence or overestimation of a spotted sonochemical activity. Finally, it is necessary to quantify the
impact of ultrasound on studied chemical systems while getting rid of technological
© The Author(s), under exclusive licence to Springer Nature Switzerland AG 2018
J.-M. Lévêque et al., Organic Sonochemistry, Ultrasound and Sonochemistry,
https://doi.org/10.1007/978-3-319-98554-1_1
1
Cavitation and Chemical Reactivity
Abstract The sound is a mechanical vibration which propagates by elasticity
through matter whatever its physical state. On liquid state, an interesting and unique
physical phenomenon was identified at the end of nineteenth century and designated as cavitation, which is the birth, growth and collapse of tiny gas bubbles.
The intensity of bubbles occurrence and of collapse violence is very dependent
on the sound frequency. The most energetic cavitation activity occurs when using
ultrasound frequencies, i.e. above the upper limit of human hearing (18 kHz). The
incident irradiative frequency is therefore of crucial importance leading to effects
on chemical systems of physical and/or chemical nature. Several other operational
parameters do also greatly influence the cavitation process and are here described as
well as most frequent types of ultrasonic devices working either on direct or indirect
mode. ‘Hotspot’ theory and generally admitted reacting zones establishing rules of
sonochemistry are also examined. Finally, some guidelines for good experimental
use of ultrasonic devices are tentatively established by authors based on their own
experience.
1.1 Introduction
To ease the reading of this Brief, necessary rudimental terms and fundamental knowledge on the origin and the nature of effects brought up by ultrasound on chemical
systems will be introduced. Some of the most common ultrasonic devices will be
also introduced. Factors impacting greatly sonochemical activity cannot be omitted, the balance between them allow to reach a maximal acoustic activity ensuring
an optimum cavitation efficiency. These are incident irradiative frequency, working
temperature, amplitude of the acoustic wave, physicochemical characteristics of the
solvent, type of dissolved gases, etc. Some good rules of use, rather based on practical experience than on theoretical rules, will be also tentatively given. Indeed, an
experimental misconduct can lead to false or even anomalous absence or overestimation of a spotted sonochemical activity. Finally, it is necessary to quantify the
impact of ultrasound on studied chemical systems while getting rid of technological
© The Author(s), under exclusive licence to Springer Nature Switzerland AG 2018
J.-M. Lévêque et al., Organic Sonochemistry, Ultrasound and Sonochemistry,
https://doi.org/10.1007/978-3-319-98554-1_1
1