根據電化學腐蝕原理,腐蝕過程中產生的電流大小可以代表腐蝕速率。由于陽極極化和陰極極化使腐蝕電池電位減小,從而降低腐蝕速率。產生陽極極化的主要原因是在腐蝕過程中,當溶液中有氧化劑時,在陽極表面產生了保護性的氧化膜,使金屬鈍化。其電位正移可達0.2~2V,可使腐蝕速率降低幾個數量級。


 工(gong)業(ye)上(shang)廣泛應(ying)用(yong)(yong)的(de)鐵、鉻(ge)、鎳、鈦及其合金(jin)的(de)活(huo)(huo)化(hua)-鈍(dun)化(hua)曲線(xian)具(ju)有(you)特殊的(de)形式,它們(men)的(de)活(huo)(huo)化(hua)-鈍(dun)化(hua)轉(zhuan)變(bian)的(de)陽(yang)極(ji)(ji)極(ji)(ji)化(hua)曲線(xian)如圖9.1所示。圖中有(you)三個(ge)不同電(dian)(dian)(dian)(dian)化(hua)學(xue)行為(wei)區(qu)域:活(huo)(huo)化(hua)區(qu)A、鈍(dun)化(hua)區(qu)P和過鈍(dun)化(hua)區(qu)T。由于極(ji)(ji)化(hua)的(de)作用(yong)(yong),隨著腐(fu)蝕(shi)電(dian)(dian)(dian)(dian)流(liu)強(qiang)(qiang)度(du)的(de)增加,陽(yang)極(ji)(ji)電(dian)(dian)(dian)(dian)位E。升(sheng)高,當陽(yang)極(ji)(ji)極(ji)(ji)化(hua)曲線(xian)達到(dao)最大值,相應(ying)電(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)位為(wei)Ep,電(dian)(dian)(dian)(dian)流(liu)強(qiang)(qiang)度(du)為(wei)Ip時(shi),產生(sheng)了陽(yang)極(ji)(ji)鈍(dun)化(hua),陽(yang)極(ji)(ji)過程受到(dao)極(ji)(ji)大障礙,此時(shi)電(dian)(dian)(dian)(dian)流(liu)強(qiang)(qiang)度(du)突然下降到(dao)最小值I最小,Ep稱為(wei)初始鈍(dun)化(hua)電(dian)(dian)(dian)(dian)位,Ip稱為(wei)臨(lin)界電(dian)(dian)(dian)(dian)流(liu)強(qiang)(qiang)度(du)。在很寬的(de)陽(yang)極(ji)(ji)電(dian)(dian)(dian)(dian)位范圍內極(ji)(ji)化(hua)時(shi),一(yi)直保持I最小的(de)腐(fu)蝕(shi)電(dian)(dian)(dian)(dian)流(liu)強(qiang)(qiang)度(du),此時(shi)腐(fu)蝕(shi)速率(lv)大大降低,陽(yang)極(ji)(ji)處于鈍(dun)化(hua)區(qu)P。


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 陽(yang)極電(dian)位超過Er后,腐(fu)蝕電(dian)流又增加(jia),這種現(xian)象稱(cheng)為過鈍化。ET稱(cheng)為過鈍化電(dian)位,陽(yang)極處于過鈍化區T,此(ci)時金(jin)屬的(de)腐(fu)蝕速率又增加(jia)。


 根據具有活化(hua)-鈍(dun)化(hua)轉(zhuan)變的金(jin)屬或合金(jin)的陽極極化(hua)曲線和陰(yin)極極化(hua)曲線的相對位置,可(ke)以分析該金(jin)屬和合金(jin)鈍(dun)化(hua)狀(zhuang)態的穩定(ding)性(xing)。