KINETICS OF NITROUS-ACID FORMATION IN NITRIC-ACID SOLUTIONS UNDER THEEFFECT OF POWER ULTRASOUND

Sonochemical nitrous acid formation was investigated in 0.1-4.0 mold m (-3) aqueous nitric acid solutions under the effect of power ultrasoun d with 20 kHz frequency. HNO2 steady-state concentration was obtained under long-time sonication; the excess HNO2 formed is decomposed and e voluted from the solution as NO and NO2 gases. The HNO2 steady-state c oncentration and the HNO2 initial formation rate depend linearly on th e HNO3 concentration and acoustic intensity (1.8-3.5 W cm(-2)) and dec rease with rising temperature in the range 21-50 degrees C. The HNO2 f ormation rate depends on the type of saturating gas as follows: Ar>N-2 >He>air. NO and O-2 are the major gaseous products of HNO3 sonication. The NO2 accumulation of in the gas phase is observed only when the de composition of. HNO2 formed becomes noticeable. The gaseous products f ormation rates depend on the HNO3 concentration, acoustic intensity an d the type of saturating gas. The mechanism of HNO2 sonochemical forma tion is assumed to be the thermal decomposition of HNO3 in the gaseous vicinity of collapsing bubbles or in the overheated liquid reaction z one surrounding the cavitational bubbles. (C) 1997 Elsevier Science B. V.