Influence of pressure on ultrasonic cavitation activity in room temperature ionic liquids: An electrochemical study

This paper provides proofs of the respective contributions of dissolved gases and solvent vapor on cavitation activity in sonoreactors. This activity can be detected by electrochemistry because the fluctuating events measured at the electrode surface are only linked to physical effects of cavitation. As ionic liquids present very low volatilities, their vaporization is reduced, and cavitation bubbles only depend on the presence of gases. Then, cavitation activity may be trigged by reactor atmosphere control. Applying severe depression within an irradiated ionic liquid medium contributes to removing dissolved gases, thus quenching cavitation activity. A specific sonoelectrochemical cell was developed for this purpose. These first results show, through electrochemical experiments, that cavitation activity markedly decreases from atmospheric pressure down to 26 kPa. Below 26 kPa, it remains very low and stable. The same experiments were carried out in acetonitrile as a witness. As expected, no depression effect is observed on cavitation activity as it is supported by the volatile solvent contribution.