抄録
It is well known that H_2O_2, HNO_2 and HNO_3 are produced when power ultrasound is irradiated into water saturated with air. Several works have investigated the concentration dependence of the chemical species for the irradiation time. However, little study on the change in pH has been reported. Especially, the effect of the dissolved gases on the pH change is not cleared. The purpose of this work is to investigate quantitativety the pH change in water saturated with different gases under sonication. Sonication was carried out under atmosphere of air, oxygen, nitrogen, and argon. The value of pH in water for different dissolved gases was obtained under a constant ultrasonic intensity. The pH measurement was carried out by Expandable Ionanalyzer (Model EA 940, Orion). The ultrasonic intensity in a reaction vessel was determined on the basis of decomposition of porphyrin (tetraphenylporphine tetrasulfonic acid, hereafter abbreviated as TPPS). In this work, we pay sufficiently attention to degassing. Under air atmosphere, the pH value changed from 7 to 4.3 for irradiation time of 30 min and after that the value approached to 3.7. On the other hand, the pH values for water saturated with Ar, N_2 and O_2 were almost independent of irradiation time. In general, the decrease of pH in water saturated with air is considered to be responsible for production of HNO_3, since production of H_2O_2 and HNO_2 does not contribution to the change in the pH. On the other hand, in water saturated with only Ar or O_2, HNO_2 and HNO_3 should not be produced for lack of nitrogen. However, slightly decrease of the pH for Ar and O_2 was observed. The amounts of decomposed TPPS in solutions saturated with O_2 and air are two times as large as that saturated with N_2. In the case of Ar, the value is about three times as large as that for N_2. The ultrasonic effect on TPPS decomposition reaction for different dissolved gases is in the order of Ar > air = O_2 > N_2, which corresponds to that of the luminescence intensity.
