Sn對Fe-Cr-(Ni)合金抗蝕能力影響研究

Effect of Sn on corrosion resistance of Sn-added Fe-Cr-(Ni) alloys

李芃(Lee Pan)

指導教授 ： 陳瑞凱 ； 吳振名

國立清華大學/工學院/材料科學工程學系/碩士(2013年)

摘要

本實驗使用兩組合金。一組以430 SS為基礎，抗腐蝕能力較差、但便宜的CS合金，另一組以Modified-20Cb3為基礎，抗腐蝕能力較優、但昂貴的S3合金。於兩組合金中，各添加不同含量的錫，利用各種電化學腐蝕量測，探討錫在合金抗腐蝕能力中，所扮演的角色。
線性極化實驗(LSV)結果顯示，不論CS合金或S3合金，都因錫的添加，使合金在腐蝕後，表面生成錫的氧化物，而因電阻極化使合金腐蝕速率下降。CS合金更因錫氧化物的生成，而可以提早進入鈍化態。但S3合金卻因本身腐蝕電位高，抗腐蝕能力極強，所以從線性極化實驗看，錫對於S3合金的影響變得不明顯。鈍化態下的腐蝕速率上升，主要係因(Ni, Fe)3(Sn, Cr)2析出相量變多所致。
在兩組合金中，錫氧化物並未形成真正具保護作用的鈍化膜。從線性極化法中，觀察到腐蝕電流密度並沒有因錫的氧化物的生成，而快速下降到鈍化電流密度；進一步比對阻抗頻譜法(EIS)的結果，得知鈍化膜的型態並沒有因錫的添加而改變。以上結果都顯示，錫氧化物無法形成像鉻氧化物Cr2¬O3那樣緻密的鈍化膜。
開路電位實驗(OCP)的結果顯示，合金鈍化膜的穩定度可以因鉻的含量增加，或因添加鎳而明顯上升。若鈍化膜有足夠穩定度，添加錫可明顯增加鈍化膜穩定度。甚至當鈍化膜損壞時，還可以修復鈍化膜；反之，添加錫，對合金鈍化膜穩定度的影響很小，或有不利影響。
綜合以上電化學實驗的結果顯示，不論在CS合金或在S3合金中，錫都提供有利於形成和維持高抗蝕能力的氧化物，如Cr2O3，的一個環境。因此可以明顯降低腐蝕速率和提高鈍化膜的穩定度。
利用循環伏安法(CV)，可以推測合金鈍化膜內的氧化物種類，並觀察到不管合金是少元傳統合金或是多元高熵合金，各元素形成的氧化物仍具有各自的獨立性，不會互相影響。搭配XPS的結果，本實驗證實兩組合金系統中存在錫的氧化物，而錫的氧化物組成為穩定的SnO2。

關鍵字

電化學腐蝕 ； 不鏽鋼 ； 錫 ； 線性極化法 ； 阻抗頻譜法 ； 開路電位法 ； 循環伏安法 ； 化學分析電子能譜儀

並列摘要

Two types of designs were used to investigate the effect of tin addition on corrosion behaviors of alloys. The first, based on type 430, cheap and less corrosion resistant, was the Cr-Sn (CS) alloys; the second, based on modified 20Cb3, expensive but corrosion resistant, was the S3 alloys. These tin-bearing alloys were characterized by a series of electrochemical measurements, including linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), open circuit potential (OCP) and cyclic voltammetry (CV).
LSV results show that both CS and S3 alloys become even corrosion resistant due to the presence of tin oxide on the surface of both alloys after corrosion and the cause of reinforced Ohmic polarization. The presence of tin oxide can even force the CS alloys to enter their passive region in an earlier stage (at lower potential), while intermetallic compound, (Ni, Fe)3(Sn, Cr)2, formed in S3 alloys with much amount of tin, that is inverse to corrosion resistant, causing corrosion rate to slightly increase in their passive region.
Although there is improvement in corrosion resistance in both alloys, the tin oxide formed on both alloys does not become as passive as chromium oxide (Cr2O3), which is really dense and protective. LSV results show that the current density does not drop to the value of passive current density immediately after CS alloys are in passive region. EIS results also show that the formation of passive film does not change with tin content in both alloys.
OCP results show that higher content of chromium and presence of nickel can improve the stability of passive film, as in the case of S3 and higher Cr content CS. If the alloys form passive films that are stable enough, addition of tin can greatly improve stability of passive films to a higher level and even repair the damaged passive films so that the alloys can stay in passive region. On the contrary, tin may have no or even inverse effect on the stability of passive film, if the passive films are not stable, as in the case of CS.
Results of CV show the same individual corrosion behavior of element for both less component CS and multi-component S3.
With the help of XPS analysis, one is able to make sure the existence of tin oxide, and its composition in both CS and S3 alloys is SnO2.

並列關鍵字

electrochemical corrosion ； stainless steel ； tin ； LSV ； EIS ； OCP ； CV ； XPS

參考文獻

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