摘要
近年來，許多研究均利用加氫水化學（Hydrogen Water Chemistry, HWC）技術，試圖降低沸水反應器（Boiling Water Chemistry, BWR）電廠主冷卻水迴路中各組件的電化學腐蝕電位（Electrochemical Corrosion Potential, ECP）。並進而防治沿晶應力腐蝕龜裂（Intergranular Stress Corrosion Cracking, IGSCC）與輻射促進應力腐蝕龜裂（Irradiation-Assisted Stress Corrosion Cracking, IASCC）的發生。然而根據文獻資料顯示，在較高飼水注氫量下（通常在0.6 ppm以上），HWC有提昇管路輻射劑量的副作用；且其對於降低壓力槽內部接近爐心出口附近組件的ECP功效並不明顯。為降低HWC技術中的注氫需求且有效降低爐心出口附近區域的ECP，我們嘗試利用抑制性被覆進行組件防蝕之可行性研究。本研究以氧化鋯（ZrO2）、氧化鈦（TiO2）及含二硝酸基氧化鋯（ZrO(NO3)2）以化學添加的方式進行覆膜處理，在模擬BWR水化學循環迴路中，針對經覆膜處理後之304不□鋼進行動態電位極化掃描分析（Potentiodynamic Polarization）、電化學腐蝕電位量測與慢應變速率拉伸測試（Slow Strain Rate Test, SSRT），藉以了解上述材料在不同被覆處理狀態下的腐蝕行為。

研究結果發現，利用動態極化掃描分析技術可發現在經過ZrO2、ZrO(NO3)2與TiO2化學添加覆膜後，其鈍化電流密度（Passive Current Density）皆比僅經預氧化（prefilm）而未覆膜的試片低。在電化學腐蝕電位量測實驗中，有經過抑制性覆膜的試片，其ECP值並非如預期的皆比未覆膜試片來的低，推測其原因可能是抑制性覆膜同時降低氧還原與不□鋼氧化的交換電流密度的結果。在慢應變速率拉伸實驗的部分，我們發現覆膜與未覆膜試片均出現嚴重的IGSCC，但未覆膜試片有相對較小的伸長量與較短的斷裂時間。

Abstract
Incidents of intergranular stress corrosion cracking (IGSCC) and irradiation-assisted stress corrosion cracking (IASCC) of stainless steel components in the primary coolant circuits of boiling water reactors (BWRs) are occurring with increasing frequency as the power reactors age. In the past decade, the hydrogen water chemistry (HWC) technique has been widely studied as a measure for mitigating IGSCC and IASCC in BWR vessel internal components. However, this technique is not without problems. In general, at a feedwater hydrogen concentration higher than 0.6 ppm, the radioactive Nitrogen-16 content in the main steam line is very likely to increase and the resulting radiation fields exert a high man-REM cost on the operator. Furthermore, it is not at all clear that HWC is effective in protecting some components against IGSCC and IASCC in terms of electrochemical corrosion potential (ECP) reduction, particularly for protecting near-core components. Therefore, new technologies, such as inhibitive coatings, were brought into consideration to enhance the effectiveness of HWC in the aspects of lower hydrogen consumption and more effective ECP reduction.

In the current study, surfaces of pre-oxidized Type 304 stainless steels (SS) were treated with various chemical compounds of TiO2, ZrO2, and ZrO(NO3)2 by chemical immersion at different temperatures. Electrochemical potentiodynamic polarization, ECP measurement, and slow strain rate tensile (SSRT) test were conducted to characterize the corrosion properties of the treated and untreated stainless steels. Test results showed that the treated SS specimens exhibited lower open circuit potentials, corrosion densities, and passive current densities than the untreated（pre-oxidized only）specimens. The ECPs of the treated and untreated specimens at 288 oC could vary by more than 200 mV at different dissolved oxygen concentrations, and the pre-oxidized specimen did not exhibit the highest ECP. According to the SSRT test results, all tested specimens showed severe IGSCC, but the pre-oxidized one had the lowest elongation and the shortest fracture time.

參考文獻
1. R. L. Cowan, Nuclear Engineering International, January 1986, p. 26.
2. M. E. Indig, "Recent Advances in Measuring ECPs in BWR Systems," Proc. 4th Intl. Symposium on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, NACE, Jekyll Island, GA., Aug. 6-10, 1989, p. 4-411.
3. Nuclear Regulatory Commission, Cracking of Vertical Welds in the Core Shroud and Degraded Repair , NRC Information Notice 97-17, April 4, 1997.
4. L. W. Niedrach, Corrosion, Vol. 47, p. 162 (1991).
5. Y. J. Kim, L. W. Niedrach, M. E. Indig, and P. L. Andresen, Journal of Metals, Vol. 44, No. 2, p. 14 (1992).
6. Tsung-Kuang Yeh and D. D. Macdonald, "Modeling the Development of Damage in BWR Primary Coolant Circuits," Proc. 7th International Symposium on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, NACE, Breckenridge, Colorado, Aug. 6-10, 1995, p. 909.
7. Y. J. Kim and P. L. Andresen, "Application of Insulated Protective Coatings for Reduction of Corrosion Potential in High Temperature Water," CORROSION/96, NACE, Denver, Colorado, Mar. 24-29, 1996, Paper Number 105.
8. R. Pathania, Zirconium Oxide Deposition to Mitigate IGSCC, BWRVIP Mitigation Committee Meeting, Atlanta, GA, October 1-3, 1997, EPRI.
9. B. Stellwag, M. Lasch, and U. Staudt, “Investigation into Alternatives to Hydrogen Water Chemistry in BWR Plants,”1998 JAIF Conference p186-193.
10. D. D. Macdonald, Corrosion, Vol. 48, No. 3, p. 194 (1992).
11. B. Stellwag, Corrosion Science, Vol. 40, No. 2, p. 337 (1998).
12. K. S. Raja et al, "Studies on Surface Oxide Films of Stainless Steels Having Simulated Post Irradiated Grain Boundary Chemistries," Proceedings of Progress in EAC Research, EAC-A/J Groups, Sendai, Japan, July 29, 1999, p. 126.
13. M. Atik et al., Journal of applied electrochemistry , Vol. 25, p. 142 (1995).
14. R. Pathania, Evaluation of ZrO2 Coatings to Mitigate IGSCC, BWRVIP Mitigation Committee Meeting, Lake Buena Vista, FL, December 1-2, 1999, EPRI.
15. Y.-J. Kim, ”Analysis of Oxide Film Formed on Type 304 Stainless Stell in 2880C Water Containing Oxygen,Hydrogen, and Hydrogen Peroxide,” CORROSION-Vol. 55, NO.1（1999）.
16. Young-Jin Kim and Peter L. Andresen, ”Application of Thermal Spary Coatings for 304 SS SCC Mitigation in High Temperature Water,”CORROSION/98 Paper No.507.
17. X. Zhou, I. Balachov and D. D. Macdonald, ”The Effect of Dielectric Coatings on IGSCC in Sensitized Type 304 SS in High Temperature Dilute Sodium Sulfate Solution, ”Corrosion Science. Vol.40 No.8 pp. 1349-1362.
18. B. Stellwag and R. Kilian, Siemens Nuclear Power GmbH U.Staudt, VGB Germany “Investigation into Alternatives to Hydrogen Water Chemistry in BWR Plants,” 3rd Workshop on LWR Coolant Water Radiolysis and Electrochemistry.
19. M.A. Al-Anezi, G.S. Frankel and A.K. Agrawal, ”Susceptibility of Conventional Pressure Vessel Steel to Hydrogen-Induced Cracking and Stress-Oriented Hydrogen-Induced Cracking in Hydrogen Sulfide-Containing Diglycolamine Solutions,” Corrosion . Vol.55 No.11 pp.1101-1109.
20. M. Shindo et al, Department of Materials Science and Engineering, Japan Atomic Energy Research Institute, “Effect of minor elements on irradiation assisted stress corrosion cracking of model austenitic stainless steels,” Journal of Nuclear Materials 233-237(1996)1393-1396.
21. A. Sanjurjo et al, SRI International, “Titanium-based coating on steel: dip coating and plasma spray,” Surface and Coatings Technology, 49(1991) 116-120.
22.李介英, 工業材料研究所, “核能電廠壓力容器內部主要組件之IASCC問題探討,” 材料與社會 第52期 80年4月.
23.開執中, 清大工科所, “IASCC反應機制之研究,” 材料與社會 第52期 80年4月.
24. R. L. Cowan et al, GE Nuclear Energy, Vallecitos Nuclear Center, “Effects of hydrogen water chemistry on radiation field buildup in BWRs,” Nuclear Engineering and Design 166(1996)31-36.
25. I. G. S. Falleiros et al, “Intergranular Corrosion in a Martensitic Stainless Steel Detected by Electrochemical Tests,” Corrosion(1999)-Vol.55, No.8, pp.769-778.
26. N. Saito et al, “Variation of Slow Strain Rate Test Fracture Mode of Type 304L Stainless Steel in 288℃ Water,” Corrosion(2000)-Vol.56, No.1, pp.57-69.
27. J. R. Galvele, “Effect of strain rate on stress corrosion crack velocity: difference between intergranular and transgranular cracking,” Corrosion Science 41(1999)191-195.
28. M. Andritschky et al, “Corrosion and adherence of stabilized ZrO2 coating at high temperatures,” Surface and Coatings Technology, 68/69(1994)81-85.
29. G. L. SONG et al, Institute of Corrosion and Protection of Metals, State Key Laboratory for Corrosion and Protection, Chinese Academy of Sciences, Shenyang, China, “Inhibitive effect of benzotriazole on the stress corrosion cracking of 18Cr-9Ni-Ti stainless steel in acidic chloride solution,” Corrosion Science, Vol.40, No.7, pp.1109-1117, 1998.
30. M. Atik and J. Zarzycki, “Protective TiO2-SiO2 coatings on stainless steel sheets prepared by dip-coating,” Journal of Materials Science Letters, 13(1994)1301-1304.
31. M. Atik and M. A. Aegerter, “Corrosion resistant sol-gel ZrO2 coatings on stainless steel,” Journal of Non-Crystalline Solids 147＆148(1992)813-819.
32. F. Perdomo L. et al, “Oxygen-free deposition of ZrO2 sol-gel films on mild stell for corrosion protection in acid medium,” Journal of materials science letters, 17(1998)295-298.
33. M. Zaharescu et al, “TiO2-based vitreous coatings obtained by sol-gel method,” Journal of Non-Crystalline Solids 160(1993)162-166.
34. Young-Joo Kim and Lorraine Falter Francis, “Processing and Characterization of Porous TiO2 Coatings,” Journal of the American Ceramic Society, Vol.76, No.3, pp.737-742(1993).
35. S. K. Yen and T. Y. Huang, Institute of Materials Engineering, National Chung Hsing University, Taiwan, “Characterization of the electrolytic ZrO2 coating on Ti-6Al-4V,” Materials Chemistry and Physics 56(1998)214-221.
36. Peter L. Andresen and Tom Angeliu, GE Corp. Research and Development Center, “The Effect of In-situ noble metal chemical addition on crack growth rate behavior of structural materials in 288℃ water,” Corrosion96, The NACE International Annual Conference and Exposition, Paper No.84.
37. L. W. Niedrach, “Effect of Palladium Coatings on the Corrosion Potential of Stainless Steel in High-Temperature Water Containing Dissolved Hydrogen and Oxygen,” Corrosion-March 1991, pp.162-169.
38. Peter L. Andresen, GE Corp. Research and Development Center, “Mitigation of Stress Corrosion Cracking by Underwater Thermal Spray Coating of Nobel Metals,” Corrosion95, The NACE International Annual Conference and Corrosion Show, Paper No.412.
39. R. Di Maggio et al, “ZrO2-CeO2 films as protective coatings against dry and wet corrosion of metallic alloys,” Surface and Coatings Technology 89(1997)292-298.
40. Dibyendu Ganguli and Debtosh Kundu, Central Glass and Ceramic Research Institute, India, “Preparation of amorphous ZrO2 coatings form metal-organic solutions,” Journal of Materials Science Letters, 3(1984)503-504.
41. K. Kato et al, “Crystal structures of TiO2 thin coatings prepared from the alkoxide solution via the dip-coating technique affecting the photocatalytic decomposition of aqueous acid,” Journal of Materials Science , 29(1994)5911-5915.
42. A. Julbe et al, “The sol-gel approach to prepare candidate microporous inorganic membranes for membrane reactors,” Journal of Membrane Science, 77(1993)137-153.
43. J. Robertson, “The mechanism of high temperature aqueous corrosion of stainless steels,” Corrosion Science, Vol..32, No.4, pp.443-465,1991.
44. D. D. Macdonald, SRI International, Menlo Park, U. S. A., “A coupled environment model for stress corrosion cracking in sensitized type 304 stainless steel in LWR environments,” Corrosion Science, Vpl.32, No.1, pp.51-81, 1991.
45. D. D. Macdonald and Mirna Urquidi-Macdonald, “Distribution functions for the breakdown of passive films,” Electrochimica Acta, Vol.31, No.8, pp.1079-1086, 1986.
46. Digby. D. Macdonald, “The point defect model for the passive state,” J. Electrochem. Soc., Vo;.139, No.12, December 1992.
47. Mirna Urquidi-Macdonald and Digby. D. Macdonald, “Theoretical analysis of the effects of alloying elements on distribution functions of passivity breakdown,” J. Electrochem. Soc., Vo;.136, No.4, April 1989.
48. H. S. Kwon and A. Wuensche and D. D. Macdonald, “Effects of flow rate on crack growth in sensitized type 304 stainless steel in high-temperature aqueous solutions,” Corrosion-Vol.56, No.5, pp.482-491, 2000.
49. M. Guglielmi et al, “Dependence of thickness on the withdrawal speed for SiO2 and TiO2 coatings obtained by the dipping method,” Journal of Materials Science, 27(1992)5052-5056.
50. M. A. Sainz et al, “UV highly absorbent coatings with CeO2 and TiO2,” Journal of Non-Crystalline Solids 121(1990)315-318.
51. Yasutaka Takahashi and Kouichi Yamaguchi, “Dip-coating conditions and modifications of lead titanate and lead zirconate titanate films,” Journal of materials science 25(1990)3950-3955.
52. F. Bel Hadj et al, “Study of thin solid films elaborated by dip coating,” Journal of Non-Crystalline Solids 82(1986)417-425.
53. C. Jeffrey Brinker and Alan J. Hurd, “Fundamentals of sol-gel dip-coating,” Journal De Physique III, 4(1994)1231-1242.
54. O. Reglat and R. Labrie and P. A. Tanguy, “A new free surface model for the dip coating process,” Journal of computational physics 109,238-346(1993).
55. Yuichi Fukaya et al, “Photoelectrochemical Protection of Stainless Alloys in BWR Primary Collant Enviroment,” tenth international conference on environmental degradation of materials in nuclear power systems-water reactors, August 5 to 9, 2001.
56. 林盈吉, “鉑覆膜之敏化304不□鋼於高溫水中應力腐蝕龜裂之研究,” 國立清華大學碩士論文.
57. 李國台, “高溫加清水化學環境對鉑貴重金屬化學被覆敏化304不□鋼之應力腐蝕研究,” 國立清華大學碩士論文.