OH-RADICAL FORMATION BY ULTRASOUND IN AQUEOUS-SOLUTION - PART II - TEREPHTHALATE AND FRICKE DOSIMETRY AND THE INFLUENCE OF VARIOUS CONDITIONS ON THE SONOLYTIC YIELD

Terephthalate and Fricke dosimetry have been carried out to determine the sonolytic energy yields of the OH free radical and of its recombin ation product H2O2 in aqueous solutions under various operating condit ions (nature of operating gas, power, frequency, temperature). For exa mple, in the sonolysis of Ar-saturated terephthalate solutions at room temperature, a frequency of 321 kHz, and a power of 170 W kg(-1), the total yield [G((.) OH)+2 G(H2O2)], equals 16 x 10(-10) mol J(-1). Thi s represents the total of (.) OH that reach the liquid phase from gas phase of the cavitating bubble. The higher the solute concentration, t he lower the H2O2 production as more of the OH free radicals are scave nged, in competition with their recombination. Fricke dosimetry, in th e absence and presence of Cu2+ ions, shows that the yield of H atom re aching the liquid phase is much lower, with G(H-.) of the order of 3 x 10(-10) mol J(-1). These sonolytic yields are smaller in solutions th at are at the point of gas saturation, and increase to an optimum as t he initial sonication-induced degassing and effervescence subsides. Th e probing of the sonic field has shown that the rate of sonolytic free -radical formation may vary across the sonicated volume depending on f requency and power input. (C) 1998 Elsevier Science B.V. All rights re served.