川島 徳道

徳岡 由一

楠元 直樹

楠元, 直樹

クスモト, ナオキ

キガ, ナナミ

ヒラオカ, シゲミ

川島, 徳道

カワシマ, ノリミチ

徳岡, 由一

トクオカ, ヨシカズ

Toin University of Yokohama Academic Repository

187Generation and Decomposition of Ozone Gas by Ozone and Ozoneless Mercury Bulbs Excited by Microwave kuSumoto Naoki 1, 2, kiga Nanami 2, hiraoka Shigemi 3, kawaShima Norimichi 4 and tokuoka Yoshikazu 1, 5 1 Graduate School of Engineering, Toin University of Yokohama 2 School of Health Sciences, Tokyo University of Technology 3 Department of Microwave Engineering, Adatara LLC. 4 Institute of International Science Education, International Pacific University 5 Faculty of Biomedical Engineering, Toin University of Yokohama （2017 年 3 月 18 日　受理）I. IntroductionOzone gas having strong oxidizing power has been used in various fields such as environmen-tal cleaning, sterilization 1), inactivation of virus, decolorization, deodorization, removal of organic substances and so on 2). Ozone gas is often pro-duced from oxygen molecules by silent discharge. Besides, it can be generated by ultraviolet light (UV light) emitted from a low-pressure mercury lamp. UV light at 184.9 nm reacts with oxygen molecules in the air to generate ozone as follow-ing 3): O2 + hν (184.9 nm) → O + O O2 + O → O3On the other hand, UV light at 253.7 nm emit-ted simultaneously with UV light at 184.9 nm from a low-pressure mercury lamp decomposes ozone via active oxygen atoms: O3 + hν (253.7 nm) → O2 + O O + O3 → 2O2It is well known that ozone gas is toxic to hu-mans. Health effect of ozone gas is summarized below. 4)0.01–0.02 ppm Odour threshold0.1 ppm Nose and throat irritation0.2–0.5 ppm Reduced visual acuity, upper airway irritation0.6–0.8 ppm Chest pain, dry cough1–2 ppm Lassitude, headache, some re-duction in lung function5–10 ppm Respiratory distress, pulse rate increase> 50 ppm Expected to be fatalMoreover, the Occupational Exposure Limits of ozone gas, which is recommended by The Japan Society for Occupational Health (JSOH), is 0.1 「桐蔭論叢」第 36 号 2017 年 6 月 〈工学研究科研究論文〉1, 2 kuSumoto Naoki, 2 kiga Nanami, 3 hiraoka Shigemi, 4 kawaShima Norimichi, and 1, 5 tokuoka Yoshikazu1 Graduate School of Engineering, Toin University of Yokohama; 2 School of Health Sciences, Tokyo University of Technology; 3 Department of Microwave Engineering, Adatara LLC.; 4 Institute of International Science Education, International Pacific University;5 Faculty of Biomedical Engineering, Toin University of YokohamaKusumoto Naoki, Kiga Nanami, HiraoKa Shigemi, KawasHima Norimichi and toKuoKa Yoshikazu188ppm (0.2 mg/m3); the maximum allowable con-centration of ozone gas established by the United States Food and Drug Administration (FDA) is 0.05 ppm (24 hours). According to the Air Pollu-tion Control Law, the environmental standard of ozone is less than 0.06 ppm/h 5) In using ozone in safety, therefore, we need to control its concentra-tion in the air.Recently, ozone generators using UV light have been employed in general home for deodor-ization and disinfection. The ozone generator with corona discharge and glow discharge, instead of UV light 6), is also utilized, because the efficien-cy of its ozone generation is higher. Since these generators have no mechanism for decomposing ozone, however, there are safety concerns in us-ing them. In addition, the ozone generator with the discharge also produces a large amount of nitro-gen oxide, NOx 7), and involves a significant cost for equipment maintenance 7).A low-pressure mercury lamp can be excited to emit UV light not only by electricity but also by microwave irradiation. In irradiation of micro-wave, gaseous mercury is exited and is changed to mercury plasma, and the low temperature plasma emits UV light 10). The mercury lamp emitting UV light by microwave needs no electrode. We then call the lamp a mercury bulb. We made two types of mercury bulbs from different quartz glass ma-terials 11, 12); one emits UV light at 184.9 and 253.7 nm to produce ozone gas, and the other does the light at 253.7nm alone to decompose ozone gas. Here, we abbreviate the former and the latter as ozone mercury bulb and ozoneless mercury bulb, respectively.We attempt to develop the ozone generator equipped each mercury bulb. The generator has a characteristic to produce and decompose ozone gas simultaneously. Moreover, the mercury bulb possesses no electrode, so it has no damage in electrode. In the present study, we investigate time-de-pendence of change in ozone concentration by ozone and ozoneless mercury bulbs excited by mi-crowave irradiation, and evaluate effect of these bulbs on generation and decomposition of ozone gas.II. Experimental method1. Ozone and ozoneless mercury bulbs.Ozone and ozoneless mercury bulbs of which the diameter was 1.5 cm were prepared. The bulb including 1, 2, and 4 mg of mercury, and the vapor presser of mercury in the light-emitting bulb was controlled at less than 0.75 torr (100 Pa).2. Generation and decomposition of ozone gas.A container (30 cm x 30 cm x 30 cm) was produced with acrylic plates, shown in Figure 1. The schematic diagram of the ozone generator used in this study is illustrated in Figure 2. The mercury bulb socket (Hg socket) of the ozone generator was placed at the center of the bottom surface of the container, and a mercury bulb was settled in the socket. A 2.45 GHz of microwave was applied to the mercury bulb to emit UV light (Figure 3). The concentration of ozone gas in Fig. 1 Acrylic container used.Generation and Decomposition of Ozone Gas by Ozone and Ozoneless Mercury Bulbs Excited by Microwave189the container was measured using a gas sampling pump equipped with a short-term quick-measur-ing detector tube for ozone gas (18 L and 18 M, GASTEC Co., Ltd.).III. ResultsFirst of all, we measured emission spectra from ozone mercury bulbs including 1, 2, and 4 mg of mercury with a spectral radiometer. Here, since the lower wavelength limit of detection of the spectra radiometer is 200 nm, we measured the spectrum at the wavelength of more than 200 nm. The spectrum from the ozone mercury bulb with 4 mg of mercury is shown in Figure 4. The large emission peak can be observed at 253.7 nm. The spectra of the other bulbs are almost the same. In addition, the fluence rate of the bulbs including 1, 2, and 4 mg of mercury are 0.564, 0.608, and 0.548 W/m2, respectively. Figure 5 depicts the time dependence of ozone concentration generated by the ozone mer-cury bulb with 1 mg of mercury. The ozone con-centration increases with increasing emission time at any illuminance and becomes almost constant after about 50 min. The constant ozone concentra-tion is 91, 120, and 162 ppm at illuminance of 610, 900, and 1200 Lx. Next, the ozone decomposition by ozoneless mercury bulb with 1 mg of mercury was carried out. The result is illustrated in Figure 6. Despite no emission of UV light, the ozone concentration in the container decreases from 20 to 6 ppm with increasing treatment time. It would be caused by leakage of ozone gas from the container and by Fig. 2 Ozone generator used.Fig. 3 Mercury bulb emitting UV light.Fig. 4 Emission spectrum from ozone mercury bulb.Fig. 5 Change in ozone concentration by ozone mercury bulb.Kusumoto Naoki, Kiga Nanami, HiraoKa Shigemi, KawasHima Norimichi and toKuoKa Yoshikazu190self-decomposition of ozone. In emission at 930 and 1000 Lx, moreover, the ozone concentration decreases immediately with an increase in irradi-ation time from 19 to 0.9 ppm and from 20 to 0 ppm.IV. DiscussionThe emission spectrum and fluence rate from the ozone mercury bulb including 1 to 4 mg of mercury is little significant difference. Further-more, the maximum ozone concentration pro-duced by ozone mercury bulb with 1 mg of mer-cury is about 160 ppm at 1000 Lx. This ozone concentration is comparable to the concentration inducing strong deodorization and sterilization for animal testing facilities, pharmaceutical manufac-turing plants, and so on. In addition, about 20 ppm of ozone can be decomposed completely by the ozoneless mercury bulb including 1 mg of mer-cury for about 2 hr. Therefore, we consider that at least 1 mg of mercury in the mercury bulb is adequate to emit UV light for producing and de-composing ozone gas.As can be seen from Fig. 5, moreover, the constant ozone concentration in more than 50 min emission time is dependent on the illuminance of the mercury bulb. That is, the ozone concentration increases with an increase in illuminance. This re-sult then indicates that we can control ozone con-centration by the illuminance of the bulb.According to the “Minamata Convention on Mercury” adopted in 2013, manufacturing, and importing and exporting of industrial products including mercury will be prohibited after 2021. Lighting equipment with mercury is no exception to the convention, and the equipment including more than 5 mg of mercury will be prohibited until the end of 2017. We suggest, however, the mercu-ry bulbs prepared are ruled out in the convention as long as it includes 1 mg of mercury.V. ConclusionWe demonstrate that the ozone and ozoneless mercury bulbs including at least 1 mg of mercury can readily generate and decompose ozone gas. We think that the ozone generator capable of ef-fectively generating and decomposing ozone gas can be produced using the mercury bulb includ-ing 1 mg of mercury, not regulated by “Minamata Convention on Mercury”.[References]1) Nagatsu M (2007) Plasma sterilization. Journal of Plasma and Fusion Research, 83: 605.2) Nishimura H (2012) The bactericidal ability of bac-teria on the agar plate medium of various electric products stating the release of airborne substances having bactericidal performance. Analysis on the main body 86th meeting of the Japan Association of Infectious Diseases Academic Lecture Chairperson Recommendation paper, 723–725.3) Devins JC. (1956) Mechanism of Ozone Formation in the Silent Electric Discharge. Journal of The Elec-trochemical Society, 103: 460–466. Fig. 6 Change in ozone concentration by ozoneless mercury bulb.Generation and Decomposition of Ozone Gas by Ozone and Ozoneless Mercury Bulbs Excited by Microwave1914) Itou T (1999) Ozone’s Wonder. pp.58. Kodansha, To-kyo.5) Kaiga N (2008) Ozone and Water Treatment. pp. 155. Gihodo Publishing, Tokyo.6) High Concentration Ozone Utilization Research Subcommittee (2007) Safety Management Standard for Ozone Utilization. pp. 18. Ministry of Economy Trade and Industry.7) Tabata N (1998) Minor Special Issue Recent trends of ozonizer, Ozone generation and generation effi-ciency. Journal of Plasma and Fusion Research, 74: 1120.8) Sugimitsu H (1996) Foundations and applications of ozone. pp. 99. Korin, Tokyo.9) Inaba K (2011) Ozone Revolution. Sagami Econom-ic Newspaper, pp. 20, Sagamihara, Kanagawa.10) Sawanobori N (2004) Development of fluorescent glass. Materials Integration, 17: 51.11) Kadono K (2009) Optical properties of glass I. NEW GLASS, 24: 59-63.12) Fujita K, Takahara Y (2007) Influence on Impurity Ultraviolet Permeability in Soda Lime. Glass Jour-nal of the Japan Institute of Metals, 71: 1071–1074.

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Generation and Decomposition of Ozone Gas by Ozone and Ozoneless Mercury Bulbs Excited by Microwave

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マイクロ波プラズマを用いた紫外線オゾン発生装置の開発

マイクロ波プラズマを用いた紫外線オゾン発生装置の開発

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