熔鹽式反應器 (Molten Salt Rector，MSR) 為第四代核反應器的一種，其可轉化用過核燃料中的錒系元素，有助解決現今用過核燃料的問題，適合作為台灣核能發展的反應器類型，但材料於高溫熔鹽的腐蝕相當嚴重，所以找出合適的結構材料成為開發MSR必須研究的題目。熔鹽的高腐蝕性源自於雜質的存在，並會對合金內特定元素造成嚴重腐蝕，尤其是Cr，所以一般挑選用於MSR的結構用材料皆採用低Cr的鎳基合金為主，不過亦有文獻指出Mo的抗熔鹽腐蝕能力是備受期待的，但相關的腐蝕研究仍不多。
本實驗選定Hastelloy-N、Hastelloy-B3以及X-750這三款不同Mo與Cr含量的鎳基合金、以及一款鉬基合金TZM進行靜態浸沒腐蝕實驗，配合自行設計的簡易熔鹽純化系統以求除去熔鹽雜質。實驗溫度為600℃，實驗時間為100、200、500、750以及1000小時，並於實驗後量測試片的質量損失，且同時利用掃描式電子顯微鏡觀察試片表面與橫截面的形貌，以探討Mo元素的抗蝕能力、與其添加到含Cr之鎳基合金的影響。
結果顯示Cr與Mo皆受到選擇性腐蝕，導致鎳基合金出現沿晶腐蝕和元素耗乏層的特徵，也導致鉬基合金因均勻腐蝕而試片厚度變薄。長時間浸沒後，三款鎳基合金的腐蝕行為由Cr與Mo在合金內部的擴散所主導，而TZM則是受熔鹽內氧化劑擴散至金屬表面的機制所主導。實驗結果顯示Cr與Mo在高Mo且少Cr含量的鎳基合金中表現較慢的擴散速率，使此類鎳基合金具更好的長期抗蝕表現。

A molten salt reactor (MSR) is a class of the Generation IV nuclear reactors. Owing to its desirable property of burning the minor actinides in spent fuel, it shows a good potential to be developed in Taiwan in order to solve the nuclear waste problem. However, the corrosion of materials is severe in high temperature molten salt environments. Therefore, searching for suitable structural materials has become an issue for MSR development.
The presence of impurities leads to the high corrosivity of molten salt, causing a severe selective corrosion on specific alloying elements, especially Cr. Therefore, a low Cr-containing Ni-based alloy was chosen as a structural material for MSR generally. Nevertheless, some previous literatures indicated that Mo was expected to exhibit good corrosion resistance to molten salt, however, there are only few correlated research studies.
Three Ni-based alloys with different Cr and Mo contents, Hastelloy-N, Hastelloy-B3 and X750, and one Mo-based alloy, TZM, were selected in this study. They were immersed in a static corrosion experimental system, equipped with a home-designed salt purification system, at 600℃ for different durations. The retrieved specimens were measured of their mass losses, and their surface and cross-sectional microstructures with corresponding element distribution analyses were examined by scanning electron microscopy and energy dispersive X-ray. The purpose is to investigate the corrosion resistance of Mo element and the influence of Mo addition on the corrosion behaviors of Cr-containing Ni-based alloys as well.
The results indicated that both Cr and Mo were selectively corroded, leading to the formations of elements depletion zones in the three Ni-based alloys and causing the thickness of the TZM specimens to decrease. The major features of corrosion attacks observed in these three Ni-based alloys and TZM were intergranular corrosion and general corrosion, respectively. The long-term changes of mass loss of the three Ni-based alloys and TZM were dominated by the diffusion of Cr and Mo through the depletion zones and the diffusion of oxidizers to the metallic surface in the molten salt, respectively. At the meantime, it was found that a higher Mo but lower Cr content in the Ni-based alloys tended to induce decreases in diffusivities of Cr and Mo in alloys, rendering these Ni-based alloys to exhibit better long-term corrosion resistances.

摘要...i
Abstract...ii
致謝...iv
目錄...v
表目錄...ix
圖目錄...x
第一章 前言與研究動機...1
第二章 文獻回顧...4
2-1 熔鹽反應器的特色...4
2-2 氟化鹽的選擇...7
2-3 熔鹽的腐蝕機制...12
2-3-1 本質腐蝕...13
2-3-2 不純物腐蝕...14
2-3-3 溫度梯度腐蝕...16
2-3-3-1 溫度對擴散控制腐蝕行為的影響...19
2-3-4 伽凡尼腐蝕...20
2-4 FLiNaK 共晶鹽類的純化...22
2-4-1 真空烘乾法...22
2-4-2 氟化氫與氫氣氣體混合法...22
2-4-3 電解精煉法...23
2-5 材料於熔鹽環境之腐蝕實驗種類...25
2-5-1 材料浸沒實驗...25
2-5-2 材料機械性質實驗...25
2-5-3 材料應力腐蝕龜裂實驗...26
2-5-4 材料輻射損傷實驗...26
2-6 熔鹽式反應器近年之研究...26
2-6-1 鉻元素的選擇性沿晶腐蝕現象...26
2-6-2 異材於熔鹽環境的伽凡尼腐蝕...29
2-6-3 材料於純化和未純化熔鹽環境的腐蝕差異...33
2-6-4 動態熔鹽環境的腐蝕行為研究...36
2-6-5 不同鉬與鉻含量的鎳基合金對熔鹽抗蝕能力的比較...37
2-6-6 含雜質的熔鹽環境對於鉬元素的影響...42
第三章 實驗原理與方法...48
3-1 靜態浸沒腐蝕實驗...49
3-1-1 實驗裝置...49
3-1-2 材料選擇...49
3-1-3 實驗過程...51
3-2 硝酸鋁溶液清洗程序...53
3-2-1 硝酸鋁溶液對Mo元素的影響...54
3-3 實驗分析儀器...55
3-2-2 掃描式電子顯微鏡(SEM)...56
3-2-3 能量散佈能譜儀(EDS)...61
第四章 結果與討論...63
4-1 質量損失結果...63
4-1-1 X-750 合金的質量損失結果...63
4-1-2 Hastelloy-N 合金的質量損失結果...64
4-1-3 Hastelloy-B3 合金的質量損失結果...66
4-1-4 TZM 合金的質量損失結果...67
4-1-5 四款合金質量損失的比較與討論...68
4-1-6 質量損失結果小總結...71
4-2 電子顯微鏡分析結果...72
4-2-1 橫截面分析...72
4-2-1-1 X-750 合金之橫截面分析...73
4-2-1-2 Hastelloy-N 合金之橫截面分析...78
4-2-1-3 Hastelloy-B3 合金之橫截面分析...82
4-2-1-4 TZM 合金之橫截面分析...87
4-2-1-5 橫截面分析結果的比較與討論...92
4-2-1-6 橫截面分析之小總結...96
4-2-2 表面分析...97
4-2-2-1 鎳基合金之表面分析...97
4-2-2-2 TZM 合金之表面分析...101
4-2-2-3 表面分析結果的比較與討論...102
4-2-2-5 表面分析之小總結...103
4-3 綜合比較...103
4-3-1 鉻與鉬含量對鎳基合金長時間腐蝕行為的影響...104
4-3-2 鎳基合金與鉬基合金的抗蝕能力比較...106
第五章 結論...108
參考文獻...111

[1] R. Gen IV, "US DOE Nuclear Energy Research Advisory Commit-tee and the Generation IV International Forum. A Technology Roadmap for Generation IV Nuclear Energy Systems. GIF002-00, December 2002," ed, 2002.

[2] R. C. Robertson, "Conceptual Design Study of a Single-Fluid Molten-Salt Breeder Reactor," ORNL-4541,Oak Ridge National Laboratory, Oak Ridge, Tennessee, 1971.

[3] L. C. Olson, J. W. Ambrosek, K. Sridharan, M. H. Anderson, and T. R. Allen, "Materials corrosion in molten LiF–NaF–KF salt," Journal of Fluorine Chemistry, vol. 130, no. 1, pp. 67-73, 2009.

[4] A. K. Misra and J. D. Whittenberger, in Proceedings of the 22nd Intersociety Energy Conversion Engineering Conference cosponsored by the AIAA ANS ASME SAE IEEE ACS and AIChE Philadelphia, 10–14 August, PA, 1987.

[5] 游柏堅, "鎳基合金於FLiNaK融鹽之腐蝕行為研究," 2010.

[6] D. J. Daimond, "Genration IV Nuclear Energy Systems: How They Got Here And Where They Are Going," Brookhaven National Laboratory, 2003.

[7] D. D. SOOD, "Molten Salt Reactor Concept," Board of Research in Nuclear Science, Bombay, 1980.

[8] K. Mitachi, T. Yamamoto, and R. Yoshioka, "Performance of a 200 MWe Molten-Salt Reactor Operated in Thorium-Uranium Fuel-Cycle," presented at the Proceedings of GLOBAL 2005, Tsukuba, Japan, Oct 9-13, 2005.

[9] S. R. Greene, Molten salts reactors: Technology History, Status and Promise (ORNL ). 2001.

[10] W. Manley, "Construction materials for molten-salt reactors," Fluid-Fueled Reactors, pp. 595-603, 1958.

[11] W. Grimes, Fluid Fuel Reactors (Chemical Aspects of Molten Fluoride Salt Reactor Fuels). Addison-Wesley, 1958.

[12] Corrosion by Molten Nitrates, Nitrites, and Fluorides. (ASM Handook vol 13A:Corrosion:Fundamentals, Testing, and Protection). ASM International, pp 124-128.

[13] M. S. Sohal, M. A. Ebner, P. Sabharwall, and P. Sharpe, "Engineering database of liquid salt thermophysical and thermochemical properties," Idaho National Laboratory Report INL/EXT-10-18297, 2010.

[14] V. Pavlík and M. Boča, "Corrosion of titanium diboride in molten FLiNaK(eut)," (in English), Chemical Papers, vol. 66, no. 11, pp. 1073-1077, 2012/11/01 2012.

[15] D. E. H. a. S. M. Cetiner, "An Overview of Liquid-Fluoride-Salt Heat Transport Systems," Oak Ridge National Laboratory, 2010.

[16] J. DeVan and R. Evans III, "Corrosion Behavior of Reactor Materials in Fluoride Salt Mixtures," ORNL/TM-328, Oak Ridge National Laboratory, Oak Ridge, TN, 1962.

[17] M. Kondo, T. Nagasaka, Q. Xu, T. Muroga, A. Sagara, N. Noda, D. Ninomiya, M. Nagura, A. Suzuki, T. Terai, "Corrosion characteristics of reduced activation ferritic steel, JLF-1 (8.92 Cr–2W) in molten salts Flibe and Flinak," Fusion Engineering and Design, vol. 84, no. 7, pp. 1081-1085, 2009.

[18] B. Laurenty, "The LM-LS experiment: investigating corrosion control, in Liquid Fluoride Salts, by Liquid alkali Metal," University of California, 2006.

[19] 王裕生, "高溫熔鹽環境中鎳基與鉬基合金之腐蝕行為研究," 2013.

[20] Denny Jones, Principles and Prevention of Corrosion, 2nd ed., Prentice-Hall, Inc., New Jersy, 1996.

[21] B. Kubíková, M. Kucharík, R. Vasiljev, and M. Boča, "Phase Equilibria, Volume Properties, Surface Tension, and Viscosity of the (FLiNaK)eut + K2NbF7 Melts," Journal of Chemical & Engineering Data, vol. 54, no. 7, pp. 2081-2084, 2009/07/09 2009.

[22] R. B. Briggs, "The Development Status of Molten-Salt Breeder Reactors,," ORNL-TM-4812, Oak Ridge National Laboratory, Oak Ridge, TN.

[23] M. Kondo. T. Nagasaka, V. Tsisar, A. Sagara, T. Muroga, T. Watanabe, T. Oshima, Y. Yokoyama, H. Miyamoto, E. Nakamura, "Corrosion of reduced activation ferritic martensitic steel JLF-1 in purified Flinak at static and flowing conditions," Fusion Engineering and Design, vol. 85, no. 7, pp. 1430-1436, 2010.

[24] U. S. A. E. Commission, Reactor Handbook: Engineering, edited by S. McLain and J.H. Martens. Interscience Publishers, 1964.

[25] M. Liu, J. Zheng, Y. Lu, Z. Li, T. Zou, X. Yu, X. Zhou, "Investigation on Corrosion Behavior of Ni-Based Alloys in Molten Fluoride Salt Using Synchrotron Radiation Techniques," Journal of Nuclear Materials, no. 1-3, 2013.

[26] C. J. Tyreman, The High Temperature Corrosion of Metals and Alloys in HF-containing Environments. University of Manchester, Institute of Science and Technology, 1986.

[27] 罔毅民, "高鎳鉬合金在熔鹽中脫溶腐蝕的研究," 中國腐蝕與防蝕學報第8期, 1981.

[28] J. W. Koger, "Corrosion And Mass Transfer Characteristics of NaBF4-NaF(92-8 mole%) In Hastelloy-N," ORNL-3866,Oak Ridge National Laboratory, Oak Ridge, Tennessee (1972).

[29] M. T. Sautman, "Molten Salt Reactor Experiment: Potential Safety Issues," Defense Nuclear Facilities Safety Board, 1995.

[30] V. B. Kirillov and V. I. Fedulov, "Corrosion resistance of 12KH18N10T steel in molten fluoride salts," Soviet materials science : a transl. of Fiziko-khimicheskaya mekhanika materialov / Academy of Sciences of the Ukrainian SSR, joural article vol. 16, no. 6, pp. 503-505, November 01 1981.

[31] 張立, 陳力俊, 梁鉅銘, 林文台, 楊哲人, 鄭晃忠, 材料電子顯微鏡學. 台灣: 國家實驗研究院 儀器科技研究中心, 1994.

[32] 汪建民, 材料分析. 台灣: 中國材料科學學會, 2004.

[33] J. Hou, G. J. Yu, C. L. Zeng, H. Ai, R. B. Xie, Y. J. Chen, X. T. Zhou, L. D. Xie, J. Q. Wang, "Effects of exposing duration on corrosion performance in weld joint of Ni-Mo-Cr alloy in FLiNaK molten salt," Journal of Fluorine Chemistry, Article vol. 191, pp. 110-119, Nov 2016.

[34] T. F. Chen, G. P. Tiwari, Y. Iijima, and K. Yamauchi, "Volume and grain boundary diffusion of chromium in Ni-base Ni-Cr-Fe alloys," Materials Transactions, Article vol. 44, no. 1, pp. 40-46, Jan 2003.

[35] G. J. Janz and N. P. Bansal, "Molten Salts Data: Diffusion Coefficients in Single and Multi‐Component Salt Systems," Journal of Physical and Chemical Reference Data, vol. 11, no. 3, pp. 505-693, 1982.

[36] C. Y. Yuh and J. R. Selman, "POLARIZATION OF THE MOLTEN-CARBONATE FUEL-CELL ANODE AND CATHODE," Journal of the Electrochemical Society, Meeting Abstract vol. 129, no. 3, pp. C117-C117, 1982.