Spatial distribution of sonochemiluminescence (SCL) from an argon-saturated luminol solution was measured in a focused sound field at 1 MHz in a standing-wave configuration. The SCL distribution was confined to pre-focal region at acoustic powers lower than 0.9 W, and was not located at the focus but at a few mm pre-focal side at a threshold for SCL inception. The threshold pressure amplitude for SCL inception was 3.6 atm at the focus, which value was obtained with a background-oriented schlieren method. The method is based on the broadening of multiple slits due to an optical deflection caused by ultrasound, and the broadening width measured provides an acoustic pressure amplitude. A qualitative image of the focused sound field was also obtained.
In this study, the amount of the radicals generated by high-intensity ultrasound radiated to the TiO2 suspension was evaluated through image processing for the degree of discoloration of methylene blue added to the suspension. As a result, we could obtain the result that in the case of 40 ml of distilled water, the 0.2 g of H2O2 with a concentration of 50 mM, the 5 g of TiO2 pellet with an average diameter of 3.85 mm, and 10 minutes the irradiating by ultrasound with an 22.7 $\times$ 10$^{3}$ (W/m$^{2}$) were the most efficient conditions for activating radicals generation.
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