Open-air type ozone generator using high-pressure micro-hollow cathode plasmas

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Open-air type ozone generator has been developed using atmospheric micro-plasmas which were formed by DC or 2.45 GHz microwave source. Oxygen at a pressure higher than atmospheric pressure passed through a small cavity of 0.2-0.5 mm in diameter where micro-plasmas were generated. The residence time of feed gas within the plasma region was microsecond order. Therefore, the plasma formation can be separated from the radical formation such as ozone and consequently the generated radicals are not dissociated by electron impacts in the micro-plasma characteristics and the ozone generation efficiency were compared between DC and microwave systems. The effects of nitrogen gas on the ozone concentration was 8.2 g/Nm3 and only 25 ppm ozone were generated in the gas mixture of 4% and 80% nitrogen mixed oxygen gas respectively. There was a threshold value of specific energy over that the ozone concentration steeply decreased. High-energy electrons dissociate the nitrogen molecules and generate NO, NO2 which accelerate the ozone decomposition in high-power-density plasmas such as a micro-hollow cathode discharge.