不鏽鋼在含氯離子環境的使用上頻繁，其所面臨的最大問題為孔蝕現象造成的損害。因此，本研究的目的為，探討增量添加鍺於肥粒鐵系430不鏽鋼(A系列)，以及鉻減量後的430不鏽鋼，添加鍺元素(B系列)，比較對「抗孔蝕」性能的影響。
本研究顯示，A系列及B系列不鏽鋼，均呈現單一BCC相結構，且沒有第二相的析出。LSV, EIS和CV電化學分析顯示，A系列不鏽鋼在鍺增量添加後，隨著添加量上升，越不易發生腐蝕，腐蝕速率降低，鈍化膜修復能力提升，電荷轉移電阻值大幅上升，鍺增量添加對A系列具有正向的影響。而在鉻減量的B系列中，因較難形成緻密的氧化鉻保護層，因此抗孔蝕能力均較差，僅C16G03在B系列中表現亮眼，擁有高的保護電位以及電荷轉移電阻值，抗孔蝕性能可以與430媲美，甚至更佳。鍺對430不鏽鋼之抗蝕能力，在電化學結果看來，有全面提升的效果。
腐蝕後的表面孔洞形貌分析，和LSV結果呈正相關，G7以上鍺增量試片表面觀察不到明顯的孔蝕痕跡，顯示鍺增量後，孔蝕有明顯改善。另外由SEI觀察發現，試片若存在熔煉縮孔，則縮孔為孔蝕發生的起點，進而腐蝕破壞。在B系列中，C16G03試片的孔蝕密度最低。C0G3的孔洞分布細小且密集，腐蝕模式由孔蝕變為均勻腐蝕。
鈍化膜之AES和XPS分析結果，顯示鈍化膜由Fe2O3, Fe3O4, Cr2O3, Cr(OH)3, CrO3, GeO和GeO2所組成；其中，鐵的氧化物主要分布在鈍化層外層，鉻的氧化物則集中分布於鈍化膜內層，而鍺的氧化物則座落在鉻的氧化物與金屬基材之間。A和B系列不鏽鋼的鈍化膜厚度，皆隨鍺增量添加而上升。
試片利用6 wt.% FeCl3水溶液進行浸泡，可以看到溶液由黃變綠，乃因黃色Fe3+與Fe反應，使Fe溶解變成綠色Fe2+的緣故。A系列鍺增量越多，重損率越低，甚至G9以上鍺增量試片幾乎沒有重量損失。B系列試片皆腐蝕嚴重，其中C16G03有最低重損率，C0G3有氧化鐵增生在表面，為均勻腐蝕的型態。
綜合以上研究，添加鍺對430不鏽鋼的抗蝕性能有良好影響，並且增量越多越有顯著的幫助，可形成GeO2於鈍化膜中，並讓鉻的氧化膜更為緻密，抵擋環境中氯離子的攻擊，提升鈍化膜之穩定性和合金整體的抗蝕性。本實驗430改良型G9以上鍺增量不鏽鋼，不但具有優良抗孔蝕性能，也可在6 wt.% FeCl3水溶液中不發生腐蝕，是本研究的重要發現。因此鍺添加對430不鏽鋼具有研究價值。

Conventional stainless steels (SSs) such as 304 and 430 are always suffered from pitting corrosion in chloride-bearing solution. This study therefore focuses on the pitting behavior of medium-Ge-contained ferritic 430SS ("Series A alloys", or abbreviated as "Alloys A"), and minor- to medium-Ge-contained "430SS" with less Cr ("Series B alloys", or abbreviated as "Alloys B").
Both Alloys A & B show BCC structure. Results from linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) indicate that Alloys A with higher Ge have more noble corrosion potentials (Ecorr), lower corrosion current densities (Icorr), growing transpassive potentials (Et) and higher charge transfer resistances (Rct) than 430SS. More Ge in 430SS gives more increase in the capability of pitting resistance. In Alloys B, the lack of Cr leads to no formation of firm and dense Cr2O3 protective layer, so that the corrosion resistance falls. However, C16G03 shows the good performance, it has the highest protection potential (Ep) and Rct among all Alloys B. Pitting resistance of C16G03 is comparable to that of 430 or better.
The surface morphologies of pits are correlated with the results of LSV. Pitting densities and pitting areas drastically drop with higher Ge. When Ge content is higher than 7.39 wt.%, number of pits are so scarce and pit size is so small that pitting density and pitting area cannot be measured. This illustrates that Ge has an improvement effect on anticorrosion of 430SS. SEI images show pitting originates from shrinkage holes from melting if any. Among Alloys B, pitting density of C16G03 is the lowest. C0G3 is more likely to be general corrosion and shows many microscopic pits.
AES and XPS show that the passive film of Ge-added 430SS is composed of Fe2O3, Fe3O4, Cr2O3, Cr(OH)3, CrO3, GeO and GeO2. Among them, iron oxides sit mainly in the outside layer of the passive film, while chromium oxides are likely to disperse in the inner layer of the film. The position of germanium oxides are in between chromium oxides and substrates. The thickness of passive films for Alloys A & B becomes thicker as Ge is more added.
The use of a 6-wt.% FeCl3 immersion test to violently corroded specimens shows that the yellow color of FeCl3 solution turns green as the Fe matrix changes to Fe2+. In Alloys A, the weight loss decreases with increasing Ge. As the amount of Ge is larger than 9.76 wt.%, there is no weight loss at all. Samples of Alloys B are heavily corroded after a 10-day immersion test. Among them, C16G03 presents the lowest weight loss and C0G3 shows general corrosion behavior with a thick film of iron oxide.
In conclusion, the Ge-modified 430SS has better corrosion resistance in chloride solution than conventional 430SS. The more Ge, the better pitting resistance for Alloys A & B. Ge modification to 430SS makes it form GeO2 and firm Cr2O3 layer in passive film to prevent from the attack of chloride ions in solution, and enhances the stability of passive film and thus prevents it from pitting. It is noted that Alloys Gx, as x is greater than 9, are not only pitting-free in chloride solution but also non-corrosive in a 6-wt.% FeCl3 solution.

[1] Y. Nakayama, Z. Ishijima, Health Promoting Appliance, US Patent 7264871 B2, 2007.
[2] 詹益愷, 國立清華大學材料科學工程研究所碩士論文 (2014)。
[3] ASM Metals Handbook - Properties and Selection: Irons Steels and High Performance Alloys, vol. 01, 10th ed., Americian Society for Metals (Materials Park, Ohio, 1990).
[4] ASM Metals Handbook - Corrosion, vols. 13A, B, & C, S.D. Cramer, B.S. Covino, eds., Americian Society for Metals (Materials Park, Ohio, 2003).
[5] W.F. Smith, Structure and Properties of Engineering Alloys, 2nd ed., McGraw-Hill (Boston, 1993).
[6] P. Marcus, Corrosion Mechanism in Theory and Practice, Marcel Dekker (New York, 2002).
[7] Alloying Elements in Stainless Steel and Other Chromium-Containing Alloys http://www.bssa.org.uk/cms/File/Euro%20Inox%20Publications/Alloying%20Elements.pdf
[8] ASM Metals Handbook - Alloy Phase Diagrams, vol. 03, H. Okamoto, M.E. Schlesinger, E.M. Mueller, eds., American Society for Metals (Materials Park, Ohio, 2016).
[9] H. Cui, J.Y. Cho, J.H. Park, H.S. Park, J.G. Park, Chemical mechanical planarization mechanism for nitrogen-doped polycrystalline Ge2Sb2Te5 film using nitric acidic slurry added with hydrogen peroxide, Journal of the Electrochemical Society, 158 (2011) H666-H670.
[10] B. Kim, K. Park, H. Kimura, Y. Park, I. Park, Influence of addition of Ge on the microstructure and corrosion properties of magnesium, Materials Transactions, 53 (2012) 240-243.
[11] F. Rosalbino, R. Carlini, R. Parodi, G. Scavino, Investigation of passivity and its breakdown on Fe3Al-Si and Fe3Al-Ge intermetallics in chloride-containing solution, Corrosion Science, 85 (2014) 394-400.
[12] F. Rosalbino, R. Carlini, R. Parodi, G. Zanicchi, Effect of silicon and germanium alloying additions on the passivation characteristics of Fe3Al intermetallic in sulphuric acid solution, Electrochimica Acta, 62 (2012) 305-312.
[13] ISO (1995) "Corrosion of metal and alloys- Evaluation of pitting corrosion", 11463, Switzerland.
[14] CNS (2002) "金屬及合金之腐蝕-孔蝕評估法", 14710, 中國.
[15] 柯賢文, 王朝正, 腐蝕及其防治, 全華圖書股份有限公司 (新北市, 2014).
[16] J.R. Galvele, Transport processes and the mechanism of pitting of metals, Journal of the Electrochemical Society, 123 (1976) 464-474.
[17] J. Bhandari, F. Khan, R. Abbassi, V. Garaniya, R. Ojeda, Moddelling of pitting corrosion in marine and offshore steel structures−A technical review, Journal of Loss Prevention in the Process Industries, 37 (2015) 39-62.
[18] M.G. Fontana, Corrosion Engineering, 3th ed., MacGraw-Hill (New York, 1986).
[19] 林逸瑋, 國立清華大學材料科學工程研究所碩士論文 (2012)。
[20] 高逸帆, 國立清華大學材料科學工程研究所碩士論文 (2008)。
[21] 李芃, 國立清華大學材料科學工程研究所碩士論文 (2013)。
[22] 李宗達, 國立清華大學材料科學工程研究所碩士論文 (2009)。
[23] 王繼敏, 不鏽鋼與金屬腐蝕, 科技圖書股份有限公司 (台北市, 1990).
[24] O.E. Barcia, O.R. Mattos, The role of chloride and sulphate anions in the iron dissolution mechanism studied by impedance measurements, Electrochimica Acta, 35 (1990) 1003-1009.
[25] D.A. Jones, Principles and Prevention of Corrosion, Pearson (New York, 1992).
[26] 楊德鈞, 金屬腐蝕學, 冶金工業出版社發行部 (北京, 1990).
[27] 葉宗洸, 腐蝕工程學, 國立清華大學工程與系統科學系 (2015)。
[28] 顏在延, 國立清華大學材料科學工程研究所碩士論文 (2011)。
[29] G.S. Frankel, Pitting corrosion of metals - A review of the critical factors, Journal of the Electrochemical Society, 145 (1998) 2186-2198.
[30] N. Ramasubramanian, N. Preocanin, R.D. Davidson, Analysis of passive films on stainless steel by cyclic voltammetry and Auger spectroscopy, Journal of the Electrochemical Society, 132 (1985) 793-798.
[31] Voltammetric Methods http://chem.libretexts.org/Textbook_Maps/Analytical_Chemistry_Textbook_Maps/Map%3A_Analytical_Chemistry_2.0_(Harvey)/11_Electrochemical_Methods/11.4%3A_Voltammetric_Methods
[32] H.D. ErtuğruL, Z.O. Uygun, Impedimetric biosensors for label-free and enzymless detection, in Impedimetric Biosensors for Label-Free and Enzymless Detection, in State of the Art in Biosensors - General Aspects, T. Rinken ed., Chapter 8, InTech (Rijeka, Croatia, 2013), pp. 179-196.
[33] F. Mansfeld, Use of electrochemical impedance spectroscopy for the study of corrosion protection by polymer coatings, Journal of Applied Electrochemistry, 25 (1995) 187-202.
[34] C. Kittel, Introduction to Solid State Physics, 8th ed., Wiley (New York, 2004).
[35] N. Sato, Anodic breakdown of passive films on metals, J. Electrochem. Soc., 129 (1982) 255-260.
[36] L. Organ, J.R. Scully, A.S. Mikhailov, J.L. Hudson, A spatiotemporal model of interactions among metastable pits and the transition to pitting corrosion, Electrochimica Acta, 51 (2005) 225-241.
[37] M.A. Amin, Metastable and stable pitting events on Al-induced by chlorate and perchlorate anions-polarization, XPS, and SEM studies, Electrochimica Acta, 54 (2009) 1857-1863.
[38] B.L. Wang, Y.F. Zheng, L.C. Zhao, Effect of Hf content and immersion time on electrochemical behavior of biomedical Ti-22Nb-xHf alloys in 0.9% NaCl solution, Materials and Corrosion-Werkstoffe Und Korrosion, 60 (2009) 330-335.
[39] A.S. Hamdy, E. El-Shenawy, T. El-Bitar, Electrochemical impedance spectroscopy study of the corrosion behavior of some niobium bearing stainless steels in 3.5% NaCl, International Journal of Electrochemical Science, 1 (2006) 171-180.
[40] M. Naghizadeh, D. Nakhaie, M. Zakeri, M.H. Moayed, The effect of dichromate ion on the pitting corrosion of AISI 316 stainless steel Part II: Pit initiation and transition to stability, Corrosion Science, 94 (2015) 420-427.
[41] G. Bianchi, A. Cerquetti, F. Mazza, S. Torchio, Electronic properties of oxide films and pitting susceptibility of type 304 stainless steel, Corrosion Science, 12 (1972) 495-502.
[42] U. Stimming, Photoelectrochemical studies of passive films, Electrochimica Acta, 31 (1986) 415-429.
[43] M. Metikoš‐Huković, M. Ceraj‐Cerić , p‐type and n‐type behavior of chromium oxide as a function of the applied potential, Journal of the Electrochemical Society, 134 (1987) 2193-2197.
[44] V. Vignal, H. Krawiec, O. Heintz, D. Mainy, Passive properties of lean duplex stainless steels after long-term ageing in air studied using EBSD, AES, XPS and local electrochemical impedance spectroscopy, Corrosion Science, 67 (2013) 109-117.
[45] K. Hashimoto, K. Asami, An X-ray photo-electron spectroscopic study of the passivity of ferritic 19Cr stainless steels in 1 N HCl, Corrosion Science, 19 (1979) 251-260.
[46] C. Calinski, H.H. Strehblow, ISS depth profiles of the passive layer on Fe/Cr alloys, Journal of the Electrochemical Society, 136 (1989) 1328-1331.
[47] N. De Cristofaro, M. Piantini, N. Zacchetti, The influence of temperature on the passivation behaviour of a super duplex stainless steel in a boric-borate buffer nsolution, Corrosion Science, 39 (1997) 2181-2191.
[48] I. Milošev, H.H. Strehblow, The behavior of stainless steels in physiological solution containing complexing agent studied by X-ray photoelectron spectroscopy, Journal of Biomedical Materials Research, 52 (2000) 404-412.
[49] C.O.A. Olsson, D. Landolt, Passive films on stainless steels: Chemistry, structure and growth, Electrochimica Acta, 48 (2003) 1093-1104.
[50] C.M. Abreu, M.J. Cristóbal, R. Losada, X.R. Nóvoa, G. Pena, M.C. Pérez, Comparative study of passive films of different stainless steels developed on alkaline medium, Electrochimica Acta, 49 (2004) 3049-3056.
[51] C.A. Gervasi, C.M. Méndez, A.E. Bolzán, P.D. Bilmes, C.L. Llorente, Chemical composition and electronic structure of anodic passive films on low-C13CrNiMo stainless steel, Journal of Solid State Electrochemistry, 20 (2016) 1065-1074.
[52] M. da Cunha Belo, B. Rondot, C. Compere, M.F. Montemor, A.M.P. Simões, M.G.S. Ferreira, Chemical composition and semiconducting behaviour of stainless steel passive films in contact with artificial seawater, Corrosion Science, 40 (1998) 481-494.
[53] S. Mischler, A. Vogel, H.J. Mathieu, D. Landolt, The chemical composition of the passive film on Fe−24Cr and Fe−24Cr−11Mo studied by AES, XPS and SIMS, Corrosion Science, 32 (1991) 925-944.
[54] A. Kocijan, Č. Donik, M. Jenko, Electrochemical and XPS studies of the passive film formed on stainless steels in borate buffer and chloride solutions, Corrosion Science, 49 (2007) 2083-2098.
[55] C.O.A. Olsson, The influence of nitrogen and molybdenum on passive films formed on the austenoferritic stainless steel 2205 studied by AES and XPS, Corrosion Science, 37 (1995) 467-479.
[56] Z. Feng, X. Cheng, C. Dong, L. Xu, X. Li, Passivity of 316L stainless steel in borate buffer solution studied by Mott–Schottky analysis, atomic absorption spectrometry and X-ray photoelectron spectroscopy, Corrosion Science, 52 (2010) 3646-3653.
[57] R. Natarajan, N. Palaniswamy, M. Natesan, V.S. Muralidharan, XPS analysis of passive film on stainless steel, The Open Corrosion Journal, 2 (2009) 114-124.
[58] K. Prabhakaran, T. Ogino, Oxidation of Ge(100) and Ge(111) surfaces: an UPS and XPS study, Surface Science, 325 (1995) 263-271.
[59] B. McEnaney, D.C. Smith, The reductive dissolution of γ-FeOOH in corrosion scales formed on cast iron in near-neutral waters, Corrosion Science, 20 (1980) 873-886.
[60] C. Giacomelli, F.C. Giacomelli, R.L. Bortolluzzi, A. Spinelli, Properties of potentiostatic passive films grown on iron electrodes immersed in weak-alkaline phosphate solutions, Anti-Corrosion Methods and Materials, 53 (2006) 232-239.
[61] K. Varga, P. Baradlai, W.O. Barnard, G. Myburg, P. Halmos, J.H. Potgieter, Comparative study of surface properties of austenitic stainless steels in sulfuric and hydrochloric acid solutions, Electrochimica Acta, 42 (1997) 25-35.
[62] J.A.L. Dobbelaar, J.H.W. de Wit, Impedance Measurements and Analysis of the Corrosion of Chromium, J. Electrochem. Soc., 137 (1990) 2038-2046.
[63] M.S. El-Basiouny, S. Haruyama, The polarization behaviour of chromium in acidic sulphate solutions, Corrosion Science, 17 (1977) 405-414.
[64] ASTM G31-12a (2012), Standard Guide for Laboratory Immersion Corrosion Testing of Metals.
[65] ASTM B895-99 (2016), Evaluating the Corrosion Resistance of Powder Metallurgy (P/M) Stainless Steel Parts/Specimens by Immersion in a Sodium Chloride Solution.
[66] ASTM G48-11 (2015), Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution.