Research On Ozone Occurrence In Discharge Jets Of Gas Mixtures Containing Oxygen

In recent years, due to prospective application potential, discharge technologies for plasma jets has attracted great attention from the world. Discharge jets have an advantage of generating chemical active species and blowing them out of discharge area, which profits not only the processing dimension of work-pieces but also the discharge stability since the processing region is separated from the discharge gap. Jet discharge technology has been widely applied in surface modification, sterilization and disinfection, environmental engineering, etc. Facing those application fields the discharge jets is demanded not only to keep stable but also to produce a variety of chemical active ingredient. Jet discharge in mixtures containing oxygen is a common scheme for active oxygen species. However, discharges in oxygen can generate inevitable ozone while produce useful oxygen species. Ozone is harmful in certain applications such as medical field. In this dissertation, ozone production in plasma jet discharge of mixtures containing oxygen is investigated to probe the ozone production kinetics.With Ar or He as carrier gas mixed with certain O2, some kinds of gas mixtures containing oxygen are prepared. A triple electrode discharge configuration is designed and driven with AC high voltage with frequency of some KHz. Measurement of discharge voltage and current waveforms and optical photos supports detailed characterization on jet discharge performance and appearance. Especially, based on measured current waveforms, the discharge conduction current waveforms are deduced for electrical calculation on discharge power and charge transportation. Comprehensive characterization on discharge current peak height, peak temporal width, the peak multiplicity and on the phase relation of the voltage waveform and the current waveform is conducted with the discharge parameters as pressure, discharge gap and oxygen ratio. Further more, it is discussed that how the discharge parameters effect ozone production such as gas species, discharge voltage, driving frequency, gas pressure, etc. The results show that the ozone synthesis in jet discharge is dynamic and synthesis and decomposition occur simultaneously. All the mentioned discharge parameters effect ozone production with reversible ways and therefore there exist optimal values.In order to enhance jet discharges, the triple electrode configuration is modified to a DC enhanced discharge scheme. A DC voltage is applied on the axial electrode, while the initial AC voltage drives the ring electrode and the plane electrode keeps grounded. By using Ar/O2, He/O2 as discharge gases, the DC enhanced jet discharges is studied in ozone production with negative or positive DC bias. The results indicate that the DC bias can enlarge the discharge volume and discharge power and therefore achieves electron density elevation, while the ozone production is kept in some sense.