| Co-Investigator(Kenkyū-buntansha) |
TERAOKA Yasutake Nagasaki University, Faculty of Engineering, Professor, 工学部, 教授 (70163904)
KANMURA Yuichi Kagoshima University, Faculty of Medicine, Professor, 医学部, 教授 (30211189)
MIURA Norio Kyushu University, Advanced Science and Technology Center for Cooperative Research, Professor, 先端科学技術共同研究センター, 教授 (70128099)
KUNIMOTO Akira Riken Corporation, R&D Division, Chief Engineer, 研究開発部, 主任技師(研究職)
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| Budget Amount *help |
¥13,600,000 (Direct Cost: ¥13,600,000)
Fiscal Year 2000: ¥4,200,000 (Direct Cost: ¥4,200,000)
Fiscal Year 1999: ¥9,400,000 (Direct Cost: ¥9,400,000)
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| Research Abstract |
Nitrous oxide (N_2O), called "laughing gas", is an anesthetic gas used extensively for surgical operations where waste N_2O is released into the atmosphere without treatment. This release may be hazardous to the atmospheric environment, since N_2O is a green-house-effect gas, the global warming coefficient of which is about 300 times higher than that of CO_2, beside being one of the gases leading to ozone layer disruption. It is thus desirable to catalytically decompose N_2O into N_2 and O_2 before release. It has recently been reported that contamination of indoor atmospheres with N_2O may cause health hazards for staff routinely working under such conditions. This project aims to develop a catalytic N_2O decomposition system and N_2O sensor.
1).N_2O sensors
In order to develop a semiconductor type gas sensor applicable to the monitoring of N_2O in air, a search for the semiconducting oxides sensitive to N_2O was carried out. Among the 23 kinds of single oxides tested, SnO_2 turned out
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to give the highest sensitivity to N_2O, although the sensitivity was not high enough. The N_2O sensitivity was found to be promoted effectively when SnO_2 was loaded with a small amount of a basic oxide such as SrO, CaO, BaO, Bi_2O_3 and Sm_2O_3. The promotion was particularly conspicuous with SrO loading. For example, 0.5wt%SrO-loaded SnO_2, exhibited the N_2O sensitivity about 3 times as high as that of pure SnO_2, and could detect N_2O in air fairly well in the concentration range of 10-300 ppm.
A stabilized-zirconia based electrochemical device attached with an oxide electrode was developed for monitoring N_2O in air at elevated temperatures. Among the 11 kinds of monoxides tested for tubular zirconia device, SnO_2 was found to exhibit the best sensing electrode properties, giving a relatively high sensitivity in air at 475 ℃. The addition of a foreign oxide (e.g., Bi_2O_3 and Sm_2O_3 to SnO_2 was effective to improve the N_20 sensitivity. Especially the element using Sm_2O_3 (0.5wt%)-SnO_2 sensing electrode exhibited the N_2O sensitivity about 1.5 times as high as that using the pure SnO_2 electrode, allowing to detect about 35 ppm N_2O in air. On the basis of the measurements of anodic and cathodic polarization curves, the sensing mechanism was confirmed to involve a mixed potential at the sensing electrode.
2).N_2O decomposition catalysts
More than 40 catalysts were subjected to the screening test ; they were transition or precious metal catalysts loaded onto oxide supports such as zeolites, Al_2O_3, TiO_2, or SiO_2. The direct decomposition of N_2O proceeded with all the catalysts tested, but the activity was strongly dependent on both the active ingredient and the support. Among these catalysts, metal-loaded Al_2O_3 exhibited the most potent decomposition activity, the actual level depending on the active ingredient (Pd>Ru>Pt). With the most active catalyst (5wt% Pd/Al_2O_3), the direct decomposition of N_20 from the dry model gas started around 250℃ and reached completion at 300℃. Although the decomposition activity was inhibited by co-existing water, 5wt%Pd/Al_2O_3 retained its high activity even in the presence of 2.3% water, N_2O decomposition starting and being completed at 300℃ and 400℃, respectively.
3).Field monitoring of N_2O at a operating room
It was found that the ambient N_2O concentration in an operating room reached 100-150ppm when a scavenging system did not work well. Especially, the N_2O concentration near a patient and/or equipment for anesthetic gas supply was more than 500 ppm. Less
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