Preliminary results on the effect of power ultrasound on nitrogen oxide and dioxide atmosphere in nitric acid solutions

The effect of ultrasound (20 kHz, 3 Wcm(-2)) on the kinetics of HNO2 and H2 O2 formation was investigated in a 1 M HNO3 medium for NO2-Ar and NO-Ar gas mixtures in various volume fractions (f(NO2) < 1.7 vol% and f(NO) < 1.1 vo l%, respectively). The H2O2 formation rate measured in 1 M HNO3 in the pres ence of N2H5NO3 was observed to be much lower than that of HNO2 without N2H 5NO3, and was relatively independent of the NO2 or NO gas volume fractions in the argon atmosphere. The HNO2 formation rate increased under ultrasound , and was higher with NO than with NO2. The induction period observed witho ut ultrasound disappeared when ultrasound was applied. The first step in th e sonochemical mechanism of HNO2 formation in the presence of NO2 involves thermal decomposition of NO2 into NO within the cavitation bubble. In the s econd step of HNO2 formation, NO reacts either with HNO3 in the cavitation bubble, or with NO2 in the cavitation bubble or at the bubble/solution inte rface. (C) 2001 Elsevier Science B.V. All rights reserved.