title: New interpretation of the effects of argon-saturating gas toward sonochemical reactions.
abstract: A number of literature reports showed that argon provides a more sonochemical activity than polyatomic gases because of its higher polytropic ratio; whereas several recent studies showed that polyatomic gases, such as O₂, can compensate the lower bubble temperature by the self decomposition in the bubble. In this work, we show for the first time a numerical interpretation of these controversial reported effects. Computer simulations of chemical reactions inside a collapsing acoustic bubble in water saturated by different gases (Ar, O₂, air and N₂) have been performed for different frequencies (213-1100 kHz). In all cases, OH radical is the main powerful oxidant created in the bubble. Unexpectedly, the order of saturating gases toward the production rate of OH radical was strongly frequency dependent. The rate of production decreases in the order of Ar>O₂>air>N₂ for frequencies above 515 kHz, and Ar starts to lose progressively its first order to the following gases with a gradually decreasing of frequency below 515 kHz up to a final order of O₂>air∼N₂>Ar at 213 kHz. The analysis of chemical kinetic results showed a surprising aspect: in some cases, there exists an optimum bubble temperature during collapse at which the chemical yield is much higher than that of the maximum bubble temperature achieved in the bubble. On the basis of this, we have concluded that the lower sonochemical activity induced by Ar for frequencies below 515 kHz is mainly due to the forte consumption of radicals inside a bubble prior the complete collapse being reached.
authors.affiliation: Laboratory of Environmental Engineering, Department of Process Engineering, Faculty of Engineering, Badji Mokhtar - Annaba University, P.O. Box 12, 23000 Annaba, Algeria; Department of Chemical Engineering, Faculty of Pharmaceutical Engineering Process, University of Constantine 3, 25000 Constantine, Algeria. Electronic address: s.merouani@yahoo.fr.
authors.forename: Slimane
authors.initials: S
authors.lastname: Merouani
authors.affiliation: Laboratory of Environmental Engineering, Department of Process Engineering, Faculty of Engineering, Badji Mokhtar - Annaba University, P.O. Box 12, 23000 Annaba, Algeria.
authors.forename: Hamza
authors.initials: H
authors.lastname: Ferkous
authors.affiliation: Laboratory of Environmental Engineering, Department of Process Engineering, Faculty of Engineering, Badji Mokhtar - Annaba University, P.O. Box 12, 23000 Annaba, Algeria.
authors.forename: Oualid
authors.initials: O
authors.lastname: Hamdaoui
authors.affiliation: Laboratory of Applied Chemistry and Materials Technology, University of Oum El-Bouaghi, P.O. Box 358, 04000 Oum El Bouaghi, Algeria.
authors.forename: Yacine
authors.initials: Y
authors.lastname: Rezgui
authors.affiliation: Laboratory of Applied Chemistry and Materials Technology, University of Oum El-Bouaghi, P.O. Box 358, 04000 Oum El Bouaghi, Algeria.
authors.forename: Miloud
authors.initials: M
authors.lastname: Guemini
keywords: ()OH radical; Computer simulations; Saturating gases; Single bubble; Sonochemical activity