Micro Shower-Source of Oxygen Radicals using Dc-Driven Atmospheric Plasmas

Summary form only given. Micro radical shower-source has been developed to generate oxygen radicals, such as ozone, O and OH to decompose persistent substances. Over atmospheric pressure gases passed through a small hole of 0.2-0.3 mm in diameter where a micro-plasma was generated. The resident time of feed gas within the cavity was shorter than msec, therefore one can utilize short lived radicals outside of the plasma. Gas flow channel was designed to spread a flow path and lower the gas temperature because ozone molecules are easily decomposed by heat. An external cooling system is quite useful too. The ozone concentration of 20 g/Nm³ and 10 g/Nm³ was obtained in pure oxygen with and without an external cooling system, respectively. These values are high enough for water purification and other industrial applications. The ozone spatial distribution measured by UV absorption showed that the ozone molecules are composed outside of the plasma where oxygen molecules are dissociated. This implied the possible utilization of the short-lived radicals such as O and OH at the outside of the plasma by combining a micro sized plasma and fast gas flow. OH radicals were generated by feeding argon with moisture and measured by LIF system. The spatial distribution of OH molecules showed the life time of them was around hundred microseconds. To evaluate the performance of the micro radical shower source, the oxygen fed plasma was directly injected into a solution of acetic acid that was the substitution of the dioxin and not decomposed by ozone molecules. The 10 ppm solution of acetic acid was decomposed and the decomposition rate largely depended on the discharge current and gas flow rate. The passage time through the electrode is crucial for effective decomposition because the life time of radicals is quite short.