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단결정 루타일 TiO2 표면에서 질소 산화물의 표면 화학 반응과 플라즈마 반응기의 광학 진단 시스템 보호를 위한 새로운 전략 개발
- Alternative Title
- Surface chemistry of nitric oxides on single crystal rutile TiO2 surfaces and the development of a new strategy for the protection of optical diagnostics system in plasma reactors
- Author(s)
- 김보성
- Alternative Author(s)
- Kim, Boseong
- Advisor
- 김유권
- Department
- 일반대학원 에너지시스템학과
- Publisher
- The Graduate School, Ajou University
- Publication Year
- 2018-02
- Language
- eng
- Keyword
- TiO2; nitric oxides; NOx; TOKAMAK; ITER; first mirror; optical diagnostics system
- Alternative Abstract
- During my Ph.D. period, I studied two different topics of (1) catalytic reduction of NO on single crystal rutile TiO2(110)–1×1 surface and (2) a new strategy for the mitigation of impurity deposition on mirrors used for optical diagnostics in fusion reactors. As a part of endeavor to elucidate the underlying catalytic processes such as selective catalytic reduction (SRC) of toxic NOx gas over oxide catalysts, we used a rutile TiO2 (110) single crystal substrate as a model oxide surface and a systematic study on the reactivity of NO over the surface has been studied using a temperature-programmed desorption technique (TPD) combined with a molecular beam technique. The results revealed interesting new details on the catalytic processes of NO over the TiO2 surface. First, N2O, which is the primary reaction product of NO on TiO2, has long been known to interact dissociatively with oxygen vacancies (VO's) on TiO2(110)-1×1 surface, but the present study clearly revealed that the interaction of N2O with VO's is non-dissociative. N2O molecules on VO's interact molecularly and desorb at a slightly higher temperature (175 K) than those bound to Ti4+ sites (135 K) on the TiO2(110) surface. The reactions of NO adsorbed on rutile TiO2(110)-1×1 to N2O occur via several distinct reaction channels over a temperature range of 50 – 500 K as labeled as a low-temperature (LT) and high-temperature (HT1 and HT2) reaction channels. Interestingly, the rutile TiO2(110)-1×1 surface provides additional reaction channel of NO to produce NH3 when the surface is hydroxylated (h-TiO2) via a reaction between NO and surface hydroxyls at lower temperatures (< 200 K). Imputiry depositon on first mirrors in optical diagnostics system has been a nagging problem in the study of fusion reactors since the impurity deposition on the mirrors commonly occurs under an operating condition and irreversibly deteriorate a reliable measurement of emission characteristics of the plasma in the reactor. Thus, a mitigation strategy for the protection of the first mirrors is highly required. Our mitigation strategy for the mitigation of the impurity deposition is to blow the impurity particles away from the mirror via a scattering in a pressurized inert gas such as helium in front of the first mirror. The technological challenge here is to confine inert gas in a specified volume in the vacuum system and this was overcome by using a baffled duct system. Detailed characteristics of gas-phase scattering of metal vapors in a flux of noble gas have been systematically studied based on the concept of classical collisional cross-sections based on the atomic radii. It was found that the > 99% mitigation of impurity deposition by the scattering requires a gas confined up to a pressure higher than 10 - 30 mTorr. Such a high pressure of inert gas was realized in a baffled tube installed in KSTAR without affecting the main chamber pressure significantly. This strategy is now considered to be promising in solving the problem of impurity deposition of the first mirrors in a nuclear fusion reactor.
- Fulltext
- Appears in Collections:
- Graduate School of Ajou University > Department of Energy Systems > 4. Theses(Ph.D)
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