WEKO3
アイテム
Development of Er2O3 Coating by MOD Method for Liquid Blankets
https://ir.soken.ac.jp/records/2674
https://ir.soken.ac.jp/records/2674c340753f-f3ab-4398-8cae-3a3d295d57e2
| 名前 / ファイル | ライセンス | アクション |
|---|---|---|
要旨・審査要旨 / Abstract, Screening Result (539.7 kB)
|
| Item type | 学位論文 / Thesis or Dissertation(1) | |||||
|---|---|---|---|---|---|---|
| 公開日 | 2012-03-23 | |||||
| タイトル | ||||||
| タイトル | Development of Er2O3 Coating by MOD Method for Liquid Blankets | |||||
| タイトル | ||||||
| タイトル | Development of Er2O3 Coating by MOD Method for Liquid Blankets | |||||
| 言語 | en | |||||
| 言語 | ||||||
| 言語 | eng | |||||
| 資源タイプ | ||||||
| 資源タイプ識別子 | http://purl.org/coar/resource_type/c_46ec | |||||
| 資源タイプ | thesis | |||||
| 著者名 |
張, 東〓
× 張, 東〓 |
|||||
| フリガナ |
チャン, ドンシュン
× チャン, ドンシュン |
|||||
| 著者 |
ZHANG, Chunfeng
× ZHANG, Chunfeng |
|||||
| 学位授与機関 | ||||||
| 学位授与機関名 | 総合研究大学院大学 | |||||
| 学位名 | ||||||
| 学位名 | 博士（工学） | |||||
| 学位記番号 | ||||||
| 内容記述タイプ | Other | |||||
| 内容記述 | 総研大甲第1450号 | |||||
| 研究科 | ||||||
| 値 | 物理科学研究科 | |||||
| 専攻 | ||||||
| 値 | 10 核融合科学専攻 | |||||
| 学位授与年月日 | ||||||
| 学位授与年月日 | 2011-09-30 | |||||
| 学位授与年度 | ||||||
| 値 | 2011 | |||||
| 学位授与番号 | ||||||
| 学位授与番号 | 12702甲第1450号 | |||||
| 要旨 | ||||||
| 内容記述タイプ | Other | |||||
| 内容記述 | In the magnetic confinement fusion reactors, blanket is one of the most important components and has the following main functions: heat generation and extraction, tritium breeding, and radiation shielding for superconductor coils. Compared with the solid breeder blankets, liquid breeder blankets are more attractive for the future DEMO reactors because of their high operation temperature, simple structure, no irradiation damage on the breeding material and no decrease in the tritium breeding capability with operation time, and so on. As the liquid breeders, liquid metal (Li, Li-Pb) and molten salt (Flibe: 2LiF+BeF2) have widely been examined. However, there are some critical issues in these liquid blankets, e.g. magneto-hydrodynamics (MHD) pressure drop in the case of liquid metal blankets and tritium permeation through the structure materials of blanket in the case of molten salt and Pb-Li blankets. To solve these issues, fabrication of ceramic coating on the surface of the metal ducts has been proposed. The candidate materials of ceramic coating need to have high tritium permeation reduction factor for application to tritium permeation reduction, and high electrical resistivity for application to MHD pressure drop mitigation, respectively. The coating materials also need to have good compatibility with the liquid breeders if the coating is to be made on the interior surfaces. Among the ceramic coating materials investigated, Er2O3 coating has been considered as a promising candidate material for the coatings in those liquid blanket systems because it showed superior compatibility with liquid Li of up to 700oC, high electrical resistivity and good deuterium permeation barrier performance when the coating was fabricated on the Reduced Activation Ferritic/Martensitic (RAFM) steels by radio frequency sputtering and filtered arc plasma deposition methods. However, these methods cannot be used to fabricate the coating on the surface of complex shapes, especially on inner surface of long ducts. The metal organic decomposition (MOD) by dip-coating method is one of the potential methods for the fabrication of coating on the complex surface, especially the pipe interiors. This method proceeds with repeated dipping into the precursor, withdrawal and drying, followed by baking. The purposes of the present study are: (1) to investigate and optimize the fabrication process of MOD Er2O3 coating with dip-coating method; (2) to examine the performance of MOD coating with respect to applications to liquid blankets; (3) to clarify the means to improve the performance of the coating according to the microstructual and microchemical characterization of the coating and the substrate. In this study, the materials used as the substrate are two kinds of ferritic steels: Fe-18Cr based commercial ferritic steel (SUS430) and Fe-9Cr-2W-0.1C based candidate Reduced Activation Ferritic/Martensitic steel (RAFM steel: JLF-1). Since the main difference in the composition of the two steels is the chromium level, the impact of the chromium level can be investigated by comparing the performances of coatings on the two substrates. MOD precursor layers, which were mainly composed of erbium carboxylate, were formed by dip-coating method and then decomposed into the Er2O3 coating by baking in an environment containing oxygen to remove the carbon of organic. Microstructure of the coating and composition of the substrate including oxidized layer were examined by SEM/EDX (Scanning Electron Microscope/Energy Dispersive X-ray Spectrometer), XPS (X-ray Photoelectron Spectroscopy) and XRD (X-Ray Diffraction). The performances of the coating for the applications to liquid blankets were examined by electrical resistivity measurements, compatibility tests with Li and hydrogen isotope permeation tests. With different speeds of withdrawal from the precursor slurry, coated specimens were fabricated with the repeated dipping for 20 times followed by baking. The coating thickness was proportional to the repetition time of the dipping and to the 2/3 power of the withdrawal speed, which is consistent with a model evaluation considering gravity, viscosity and surface tension of the precursor slurry. When Er2O3 coatings on SUS430 substrate were baked in air, erbium organic completely decomposed above 450oC and formed the Er2O3 coating with cubic phase according to the XRD analysis of coating. When baked at 600oC for better crystallinity in air, thin oxidized layer (<0.1µm) with main composition of Cr2O3 was formed below the coating. At room temperature, the coating with thickness of 0.5µm had high electrical resistivity up to 1011Ωm which satisfied the design requirement of liquid Li blankets (104Ωm). The coating survived after the static Li exposure test for 280h at 500oC, which means that it has good compatibility with Li. Compared with the bare SUS430 substrate, coated specimen has a deuterium permeation reduction factor of about 50 at 600oC. When Er2O3 coating on JLF-1 substrate was baked at 600oC in air, the coating almost peeled off from the substrate after static Li exposure test for 5h at 500oC and had hydrogen permeation reduction factor of only 15 at 600oC. From the elemental depth profile of the coating with XPS analysis, thick Fe2O3 layer was formed on JLF-1 substrate. Coating surface on JLF-1 substrate was very rough compared with that on SUS430 substrate. The reason of the inferior performances of the coating on JLF-1, relative to that on SUS430 seems to be attributed to the Fe2O3 layer, which has a very different coefficient of thermal expansion from that of Er2O3 compared with Cr2O3 and, thus could introduce small cracks in the coating during the cooling down after the baking. Because JLF-1 has low chromium level and high oxidization potential in air compared with high chromium level of SUS430, decrease of oxygen partial pressure in the baking atmosphere is considered to be a possible way to suppress the formation of Fe2O3 layer in the oxidized layer of JLF-1 surface. To suppress the formation of Fe2O3 layer and remove the carbon of organic, coating on JLF-1 substrate was baked at 700oC for 1h in commercially pure Ar where oxygen impurity was ~10ppm during the baking process in the furnace. XPS analysis showed that erbium organic was completely decomposed into Er2O3 without the remaining carbon and a Cr2O3 layer was formed in the oxidized layer. In this case, the coating had a smooth surface without the cracks compared with those baked in air while some bulgy parts including carbides or carbon were found. After the static Li exposure test for 5h at 500oC, the coating still covered 70% area of the specimen. Though the stability of coating was improved, further improvement is necessary to reduce the bulgy parts of carbon or carbides whose dissolution into Li lead to the exfoliation of coating. Hydrogen permeation reduction factor of the coating was increased from 15 to ~100 at 600oC by changing the baking atmosphere from air to Ar. The coatings on JLF-1 and SUS430 were also fabricated by baking at different temperatures in baking atmospheres with different oxygen partial pressures. The results showed that high baking temperature and low oxygen partial pressure were effective to form Cr2O3 layer on JLF-1 substrate. A model could qualitatively explain the formation condition of Cr2O3 which was affected by the baking temperature, oxygen partial pressure and chromium level of substrate. The formation of Cr2O3 layer depends on the balance between the diffusion flux of chromium cations from the substrate and the supply of the oxygen anions which diffused through the coating layer from the baking atmosphere. The low oxygen pressure would suppress the formation of Fe2O3 by decreasing the diffusion flux of oxygen anions through the coating layer and the high temperature would enhance the diffusion of chromium cations to the substrate surface inducing formation of the Cr2O3 layer on JLF-1. In summary, dip-coating by MOD method is suitable for the coating of Er2O3 on large area and complex surfaces because it is a simple process and is controllable of thickness. The coating with thickness of 0.5µm had high electrical resistivity and almost satisfied the design requirement of liquid Li blankets. In the case of high Cr steel substrate of SUS430, baking in air induced formation of Cr2O3 layer on the substrate, which kept the good coating performances with respect to surface smoothness, compatibility with Li and hydrogen permeation reduction. However, in the case of low Cr steel substrate of JLF-1, the baking in air induced thick Fe2O3 layer, resulting in much inferior coating properties. Very different coefficient of thermal expansion of Fe2O3 from that of Er2O3, which could lead to micro cracking of the coating by the temperature change, is considered to be responsible. By decreasing the oxygen partial pressure in the baking atmosphere and increasing baking temperature, Cr2O3 layer was formed instead of thick Fe2O3 layer on JLF-1 substrate surface and then the coating performances were improved significantly. Thus it is critically important to avoid the formation of Fe2O3 layer by controlling the oxygen partial pressure of the baking atmosphere. By systematic tests with different baking temperatures and oxygen partial pressures, the conditions to avoid the formation of Fe2O3 layer were indicated for the two steels, and possible mechanisms of the effects of these parameters were identified by a model considering diffusion of oxygen anions and chromium cations in the coating and the substrate, respectively. However, the control of baking atmosphere would not be sufficient for the coating on JLF-1 to have high compatibility with liquid Li. Enrichment of Cr in the surface of the substrate or use of high Cr level RAFM substrate could be possible ways for further improvements. |
|||||
| 所蔵 | ||||||
| 値 | 有 | |||||
| フォーマット | ||||||
| 内容記述タイプ | Other | |||||
| 内容記述 | application/pdf | |||||
| 著者版フラグ | ||||||
| 出版タイプ | VoR | |||||
| 出版タイプResource | http://purl.org/coar/version/c_970fb48d4fbd8a85 | |||||
