現階段腐蝕實驗是探究金屬(shu)腐蝕以及防護的主要手段，通過腐蝕實驗可以探究金屬發生腐蝕的規律及機理、檢查并篩選金屬材料的材質、估算金屬材料的使用壽命、分析金屬材料腐蝕事故的原因以及驗證防腐蝕的效果等。目前探究金屬腐蝕以及防護的方式有多種，如表面分析法、失重法以及電化學法。因為大部分金屬產生的腐蝕都是電化學腐蝕，而腐蝕過程中發生的電化學反應為電化學腐蝕的本質，所以金屬／電解質界面（雙電層）的電化學性質被大量使用于探究金屬腐蝕發生的規律、腐蝕產生的機理等方面。因此，在現有的研究金屬腐蝕與防護的方法中，電化學方法是一種較為重要的方法。腐蝕電化學法能夠按照腐蝕金屬電極特點的不同而分為以下三種類型：①. 電化學動力研究方法，指利用控制極化電流及電極電位來測定腐蝕體系中的熱力學參數；②. 獨用的腐蝕電化學測量跟研究法，指按照金屬電化學腐蝕的獨特性建立相應的電化學測量跟研究方法；③. 通過模擬裝置來探究具有獨特腐蝕形態的電化學測試技術，如模擬SSRT裂紋尖端的裝置、研究縫隙腐蝕的閉塞電池等。這幾種方法中最基礎的為電化學動力法。


  電(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)位以及電(dian)(dian)(dian)流密度(du)為腐蝕電(dian)(dian)(dian)化學(xue)實驗所(suo)要(yao)獲得(de)的(de)(de)(de)重要(yao)參數(shu)，其(qi)中電(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)位表(biao)示電(dian)(dian)(dian)解液(ye)－金屬界(jie)面的(de)(de)(de)特性和(he)結構；電(dian)(dian)(dian)流密度(du)表(biao)示金屬材(cai)料表(biao)面上單位面積(ji)內電(dian)(dian)(dian)化學(xue)反應進行的(de)(de)(de)快慢。絕大多數(shu)電(dian)(dian)(dian)化學(xue)測試都是測定電(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)位跟(gen)電(dian)(dian)(dian)流密度(du)這兩者間的(de)(de)(de)關聯。


 與其他電(dian)(dian)(dian)化學(xue)(xue)(xue)過程（如電(dian)(dian)(dian)鍍、電(dian)(dian)(dian)解及化學(xue)(xue)(xue)電(dian)(dian)(dian)源等）相比，金屬電(dian)(dian)(dian)化學(xue)(xue)(xue)腐蝕測量過程的對象是(shi)金屬電(dian)(dian)(dian)極，該過程有(you)如下特點：


   1. 金(jin)屬發生腐蝕的整個(ge)腐蝕體(ti)系由(you)數個(ge)電(dian)極(ji)(ji)反(fan)應耦合而成，同時(shi)在整個(ge)電(dian)極(ji)(ji)表面上也發生著數個(ge)電(dian)極(ji)(ji)反(fan)應，所以與只具有(you)一個(ge)電(dian)極(ji)(ji)反(fan)應的電(dian)極(ji)(ji)系統相比，其在分析和(he)處(chu)理腐蝕電(dian)化學(xue)實驗結果上有(you)著一定特別之處(chu)。


  2. 電(dian)極(ji)金(jin)(jin)屬材料發生陽極(ji)溶解反應(ying)(ying)，即(ji)腐蝕金(jin)(jin)屬自身參與(yu)的反應(ying)(ying)是(shi)電(dian)極(ji)系統中(zhong)電(dian)極(ji)反應(ying)(ying)中(zhong)的一種(zhong)。


  3. 測量(liang)過程中(zhong)不可以只探究(jiu)整個電極(ji)表面(mian)總(zong)的(de)電化學(xue)行為(wei)(wei)，因為(wei)(wei)電極(ji)表面(mian)表現(xian)為(wei)(wei)多層結構，金屬電極(ji)上有(you)(you)著腐(fu)蝕(shi)產物銹層、腐(fu)蝕(shi)孔及表面(mian)膜，導致電極(ji)表面(mian)具有(you)(you)不光滑(hua)的(de)特點，容易發生各種形式的(de)局部(bu)腐(fu)蝕(shi)，所以有(you)(you)必要發展(zhan)如微(wei)區電化學(xue)測試之類(lei)的(de)能夠(gou)表征電極(ji)表面(mian)不均勻性的(de)研(yan)究(jiu)方法。


  4. 腐蝕金屬(shu)的電極(ji)反應相對(dui)于其他一(yi)些電化學過程而言比(bi)較(jiao)緩慢。


 此外，腐蝕電化學測(ce)試方(fang)法為原位(wei)技術(shu)，能夠比較真(zhen)實地反應金屬(shu)電極表面發(fa)生的(de)(de)實際腐蝕，擁(yong)有較強(qiang)的(de)(de)靈(ling)敏度、操作簡單(dan)容易實施且實時性好(hao)的(de)(de)優點。電化學實驗常(chang)用(yong)的(de)(de)方(fang)法有極化曲線、交流阻抗及電位(wei)掃描等。


  極(ji)(ji)化(hua)曲(qu)線的測量(liang)有利于研究電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)過程的影響(xiang)因(yin)素和機理。眾所(suo)周知，當我們探究可逆(ni)電(dian)(dian)(dian)(dian)(dian)池的反應時電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)上基(ji)本上是(shi)不(bu)(bu)存在電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的，各個電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)的反應基(ji)本都在平(ping)衡(heng)狀(zhuang)態下(xia)發生，所(suo)以該反應為可逆(ni)的。但(dan)是(shi)一旦存在電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)通過，電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)原(yuan)本的平(ping)衡(heng)狀(zhuang)態就(jiu)被(bei)打破，進而導致(zhi)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)位(wei)偏(pian)(pian)離原(yuan)本的平(ping)衡(heng)電(dian)(dian)(dian)(dian)(dian)位(wei)值，導致(zhi)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)反應處于一種(zhong)(zhong)不(bu)(bu)可逆(ni)的狀(zhuang)態，不(bu)(bu)可逆(ni)程度(du)隨著電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)密度(du)的升高而增強，即(ji)所(suo)謂的電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)極(ji)(ji)化(hua)就(jiu)是(shi)指(zhi)由于電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)通過電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)而導致(zhi)電(dian)(dian)(dian)(dian)(dian)位(wei)偏(pian)(pian)離平(ping)衡(heng)值的一種(zhong)(zhong)現狀(zhuang)，極(ji)(ji)化(hua)曲(qu)線即(ji)表示電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)位(wei)與電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)密度(du)兩者間的關系，其(qi)測試有以下(xia)幾種(zhong)(zhong)方法(fa)。


a. 恒(heng)電位法


  恒電(dian)(dian)(dian)(dian)位(wei)法(fa)(fa)即將被研究的(de)(de)(de)電(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)位(wei)固定在不同(tong)的(de)(de)(de)電(dian)(dian)(dian)(dian)位(wei)上(shang)，然后測(ce)試(shi)對(dui)應(ying)電(dian)(dian)(dian)(dian)位(wei)下(xia)的(de)(de)(de)電(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)流(liu)密(mi)度，在實(shi)際應(ying)用過程(cheng)中使(shi)用較為(wei)普遍的(de)(de)(de)是靜(jing)態(tai)法(fa)(fa)及(ji)動態(tai)法(fa)(fa)。所謂靜(jing)態(tai)法(fa)(fa)是指控(kong)制電(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)位(wei)為(wei)某(mou)一個(ge)特(te)定值，測(ce)量(liang)相對(dui)應(ying)電(dian)(dian)(dian)(dian)位(wei)下(xia)的(de)(de)(de)電(dian)(dian)(dian)(dian)流(liu)密(mi)度，且依次測(ce)定整個(ge)電(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)位(wei)下(xia)的(de)(de)(de)電(dian)(dian)(dian)(dian)流(liu)密(mi)度，從而(er)得(de)到整個(ge)極(ji)化(hua)曲(qu)(qu)(qu)線(xian)；其次動態(tai)法(fa)(fa)指控(kong)制電(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)位(wei)按照較為(wei)緩慢的(de)(de)(de)速(su)度不停地變(bian)化(hua)，并且測(ce)量(liang)相對(dui)應(ying)電(dian)(dian)(dian)(dian)位(wei)下(xia)的(de)(de)(de)電(dian)(dian)(dian)(dian)流(liu)值，瞬時電(dian)(dian)(dian)(dian)流(liu)與其相對(dui)應(ying)的(de)(de)(de)電(dian)(dian)(dian)(dian)位(wei)關系曲(qu)(qu)(qu)線(xian)即為(wei)極(ji)化(hua)曲(qu)(qu)(qu)線(xian)。這兩種方(fang)法(fa)(fa)中較為(wei)廣泛使(shi)用的(de)(de)(de)是動態(tai)法(fa)(fa)測(ce)定極(ji)化(hua)曲(qu)(qu)(qu)線(xian)，該方(fang)法(fa)(fa)的(de)(de)(de)優點在于(yu)(yu)掃描(miao)速(su)度可(ke)以控(kong)制、可(ke)以自動測(ce)量(liang)并繪制極(ji)化(hua)曲(qu)(qu)(qu)線(xian)，其測(ce)量(liang)的(de)(de)(de)結(jie)果有較高的(de)(de)(de)重現性，對(dui)于(yu)(yu)那(nei)些需要比較的(de)(de)(de)實(shi)驗該方(fang)法(fa)(fa)為(wei)首選。


b. 恒電流法


  恒(heng)電(dian)(dian)流法是(shi)指固定(ding)電(dian)(dian)極(ji)體(ti)系的(de)電(dian)(dian)流密(mi)(mi)度為某一特定(ding)值，測(ce)定(ding)跟電(dian)(dian)流密(mi)(mi)度相對應(ying)的(de)電(dian)(dian)極(ji)電(dian)(dian)位。恒(heng)電(dian)(dian)流法測(ce)量(liang)(liang)極(ji)化曲線在測(ce)定(ding)過(guo)程中(zhong)(zhong)電(dian)(dian)極(ji)很難達到一個穩定(ding)的(de)狀態，所以在實際測(ce)量(liang)(liang)過(guo)程中(zhong)(zhong)一般當(dang)電(dian)(dian)位接近穩定(ding)的(de)時(shi)候即可以讀值。


  典型的動電位極化曲線如圖5.1所示。圖中Eb為金屬材料的點蝕電位，Ep為保護電位。同樣的實驗狀態下點蝕電位（Eb)值越大則意味著金屬產生點腐蝕的傾向越低；當幾種金屬材料的點蝕電位值相當，只有將點蝕電位和保護電位綜合考慮才能評價金屬的耐蝕能力，（Eb-Ep)差值越低表明材料鈍化膜修復能力越強，耐孔蝕性能越優，因而保護電位（Ep)和點蝕電位（Eb)是被用來表示金屬耐孔腐蝕能力大小的基本參數。在E>Eb的條件下，點蝕必然會發生，不但原來具有的蝕孔會長大而且還會產生新的蝕孔；在E<Ep的情況下不會發生點蝕，原來的孔蝕不會長大而且新的蝕孔也不會產生；在Ep<E<Eb條件下，孔蝕存在，原有的蝕孔會接著擴展并生長，但是新蝕孔不會產生。


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  電化學阻抗譜（Electrochemical Impedance Spectroscopy,EIS),在早期的電化學文獻中電化學阻抗又被稱為交流阻抗（Alternating Current impedance,AC im-pedance).電化學阻抗原先被用于電學中來探究線性電路網絡頻率響應特征，后來被用在電極上，進而成為電化學的研究方式。電化學阻抗譜的原理是指向電化學體系施予一頻率各異的小振幅交流電動勢，測定正弦波頻率（ω)的改變對該電動勢與電流信號比值產生的影響，即測定阻抗隨著正弦波頻率（ω)的變化，也可以通過測定阻抗的相位角Φ隨ω的變化來分析電極材料、腐蝕機理、導電材料、電極過程的動力學等方面的機理。采用小振幅的電信號既能夠防止給系統帶來較大的影響，同時又能夠讓擾動跟響應體系之間表現為近似線性的關系，進而讓測量的結果數學處理更容易。此外，電化學阻抗譜是通過測量過程中獲得的頻率比較寬的阻抗譜探究電極的，所以相對于另外一些電化學法其能夠得到電極界面結構和動力學信息。例如：通過阻抗譜形狀能夠探究金屬電極發生腐蝕的機理；探究金屬表面上保護膜的阻抗特征；對腐蝕金屬進行電化學阻抗測量可以獲得極化電阻（Rp);對腐蝕的金屬材料進行電化學阻抗譜測量，能夠了解動力學參數進而來研究金屬材料抗腐蝕能力的強弱等。因此，電化學阻抗譜成為近年來探究金屬發生腐蝕與采取相應防護措施的重要方式。


  電(dian)(dian)(dian)(dian)(dian)(dian)化(hua)學(xue)阻(zu)抗(kang)（EIS)測試把電(dian)(dian)(dian)(dian)(dian)(dian)化(hua)學(xue)系統(tong)作(zuo)為(wei)一(yi)個等效(xiao)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)，交(jiao)流阻(zu)抗(kang)實(shi)驗(yan)的(de)(de)基本等效(xiao)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)如圖5.2所示。該電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)的(de)(de)組(zu)(zu)成元(yuan)(yuan)件(jian)(jian)有電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)（R:金屬材料對電(dian)(dian)(dian)(dian)(dian)(dian)流的(de)(de)阻(zu)攔(lan)功能(neng)）、電(dian)(dian)(dian)(dian)(dian)(dian)感（L:于電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)中對交(jiao)流電(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)阻(zu)礙(ai)(ai)功能(neng)）及(ji)電(dian)(dian)(dian)(dian)(dian)(dian)容（C:電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)中對交(jiao)流電(dian)(dian)(dian)(dian)(dian)(dian)所引起的(de)(de)阻(zu)礙(ai)(ai)作(zuo)用）等，這些(xie)元(yuan)(yuan)件(jian)(jian)按照(zhao)串聯(lian)或者并聯(lian)的(de)(de)方式(shi)組(zu)(zu)合(he)起來形成一(yi)個等效(xiao)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)。測量電(dian)(dian)(dian)(dian)(dian)(dian)化(hua)學(xue)阻(zu)抗(kang)能(neng)夠確定等效(xiao)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)的(de)(de)組(zu)(zu)成方式(shi)及(ji)各(ge)組(zu)(zu)成元(yuan)(yuan)件(jian)(jian)的(de)(de)值、通過這些(xie)元(yuan)(yuan)件(jian)(jian)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)化(hua)學(xue)含義就可以分(fen)析電(dian)(dian)(dian)(dian)(dian)(dian)化(hua)學(xue)電(dian)(dian)(dian)(dian)(dian)(dian)極過程的(de)(de)性質和電(dian)(dian)(dian)(dian)(dian)(dian)化(hua)學(xue)系統(tong)的(de)(de)結(jie)構。



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