一(yi)塊金(jin)(jin)(jin)屬(shu)，表面看來(lai)挺光滑，可是在顯微鏡(jing)下就會發現，它的(de)(de)結(jie)構(gou)很不均勻，這就為“病從口(kou)入”大開了方(fang)便之(zhi)門，因為金(jin)(jin)(jin)屬(shu)遍體都是“口(kou)”，準(zhun)確一(yi)點說(shuo)，不是病從口(kou)入，而是病從“皮”入了。所(suo)以(yi)金(jin)(jin)(jin)屬(shu)的(de)(de)常見病--腐(fu)蝕，一(yi)般都開始于(yu)“皮膚病”。首先是金(jin)(jin)(jin)屬(shu)“皮膚潰瘍”，然后逐漸侵入到內部。由于(yu)金(jin)(jin)(jin)屬(shu)接觸的(de)(de)物質(zhi)多種(zhong)多樣，“得病”的(de)(de)條件也各不相同，所(suo)以(yi)金(jin)(jin)(jin)屬(shu)的(de)(de)常見病還可以(yi)分(fen)為許(xu)多種(zhong)。也就是說(shuo)，金(jin)(jin)(jin)屬(shu)腐(fu)蝕可以(yi)分(fen)為許(xu)多種(zhong)類。

金屬腐(fu)(fu)蝕(shi)分(fen)類的(de)(de)方法很多，常見的(de)(de)一種就是(shi)根據腐(fu)(fu)蝕(shi)過(guo)程(cheng)中(zhong)是(shi)否有電流產生，分(fen)為(wei)化學(xue)腐(fu)(fu)蝕(shi)和電化學(xue)腐(fu)(fu)蝕(shi)兩類。化學(xue)腐(fu)(fu)蝕(shi)一般是(shi)在(zai)干(gan)(gan)燥和高(gao)溫的(de)(de)環境(jing)下發(fa)生的(de)(de)，它是(shi)金屬的(de)(de)“干(gan)(gan)熱(re)病”；電化學(xue)腐(fu)(fu)蝕(shi)是(shi)在(zai)潮濕(shi)(shi)的(de)(de)環境(jing)下發(fa)生的(de)(de)，它是(shi)金屬的(de)(de)“風濕(shi)(shi)病”。

 化(hua)學腐(fu)蝕(shi)是(shi)金(jin)屬在不(bu)導電環境中(zhong)(zhong)的腐(fu)蝕(shi)，它是(shi)金(jin)屬與(yu)某種(zhong)(zhong)物質直接接觸時發生的化(hua)學反(fan)(fan)應。在化(hua)學腐(fu)蝕(shi)中(zhong)(zhong)，和金(jin)屬接觸發生反(fan)(fan)應的物質可以是(shi)氣(qi)體，也可以是(shi)液(ye)體，所以化(hua)學腐(fu)蝕(shi)又分為氣(qi)體腐(fu)蝕(shi)和液(ye)體腐(fu)蝕(shi)兩種(zhong)(zhong)。

 在(zai)高溫下，或(huo)周圍沒(mei)有(you)導電物(wu)質的(de)條件下，金(jin)屬與(yu)空氣或(huo)其他其他發生(sheng)反應(ying)，表(biao)面(mian)生(sheng)成(cheng)氧(yang)化物(wu)或(huo)其他化合(he)(he)物(wu)的(de)現象，稱(cheng)為氣體(ti)腐蝕。自然(ran)界(jie)中，氣體(ti)腐蝕的(de)現象也是(shi)很多。例如，鐵(tie)在(zai)空氣中或(huo)氧(yang)氣中加熱時，表(biao)面(mian)會(hui)生(sheng)成(cheng)鐵(tie)的(de)氧(yang)化物(wu)膜(mo)；鋁在(zai)空氣中會(hui)與(yu)氧(yang)氣反應(ying)，表(biao)面(mian)生(sheng)成(cheng)一(yi)層氧(yang)化鋁薄膜(mo)。像這樣，金(jin)屬與(yu)周圍的(de)物(wu)質接觸發生(sheng)反應(ying)生(sheng)成(cheng)了化合(he)(he)物(wu)，我們就說(shuo)金(jin)屬被(bei)腐蝕了，生(sheng)成(cheng)的(de)化合(he)(he)物(wu)（膜(mo)）就是(shi)腐蝕的(de)產物(wu)（常(chang)稱(cheng)作銹）。

金(jin)屬(shu)在不導(dao)電(dian)的(de)(de)液(ye)體里的(de)(de)腐(fu)(fu)蝕(shi)(shi)也是一種化(hua)(hua)(hua)學(xue)(xue)腐(fu)(fu)蝕(shi)(shi)，叫做液(ye)體腐(fu)(fu)蝕(shi)(shi)。銀(yin)(yin)可(ke)與碘(dian)發(fa)生液(ye)體腐(fu)(fu)蝕(shi)(shi)。例如把碘(dian)溶(rong)(rong)解(jie)于(yu)乙(yi)(yi)醚(mi)中(zhong)(zhong)，制成碘(dian)的(de)(de)乙(yi)(yi)醚(mi)溶(rong)(rong)液(ye)。乙(yi)(yi)醚(mi)是一種有機(ji)物(wu)，不能(neng)導(dao)電(dian)。把銀(yin)(yin)塊投入溶(rong)(rong)液(ye)中(zhong)(zhong)，溶(rong)(rong)解(jie)了的(de)(de)碘(dian)能(neng)夠與銀(yin)(yin)反(fan)應(ying)(ying)，在銀(yin)(yin)的(de)(de)表(biao)面(mian)生產碘(dian)化(hua)(hua)(hua)銀(yin)(yin)膜。石(shi)(shi)(shi)油(you)中(zhong)(zhong)往(wang)往(wang)含(han)有硫(liu)(liu)(liu)、硫(liu)(liu)(liu)化(hua)(hua)(hua)氫及某些含(han)硫(liu)(liu)(liu)的(de)(de)有機(ji)物(wu)，石(shi)(shi)(shi)油(you)中(zhong)(zhong)還含(han)有少(shao)量水，這(zhe)少(shao)量的(de)(de)水一般不能(neng)與硫(liu)(liu)(liu)的(de)(de)化(hua)(hua)(hua)合物(wu)形(xing)成導(dao)電(dian)溶(rong)(rong)液(ye)，但它(ta)卻能(neng)加速(su)硫(liu)(liu)(liu)的(de)(de)化(hua)(hua)(hua)合物(wu)與金(jin)屬(shu)發(fa)生化(hua)(hua)(hua)學(xue)(xue)反(fan)應(ying)(ying)，成為反(fan)應(ying)(ying)的(de)(de)催化(hua)(hua)(hua)劑。例如，硫(liu)(liu)(liu)化(hua)(hua)(hua)氫可(ke)與鐵、鉛、銅(tong)、汞(gong)、銀(yin)(yin)等反(fan)應(ying)(ying)，生成這(zhe)些金(jin)屬(shu)的(de)(de)硫(liu)(liu)(liu)化(hua)(hua)(hua)物(wu)，單質硫(liu)(liu)(liu)也可(ke)與銅(tong)、汞(gong)、銀(yin)(yin)等金(jin)屬(shu)反(fan)應(ying)(ying)，所以儲存石(shi)(shi)(shi)油(you)的(de)(de)容器上(shang)部(bu)或蓋(gai)子往(wang)往(wang)被硫(liu)(liu)(liu)化(hua)(hua)(hua)氫腐(fu)(fu)蝕(shi)(shi)。在煉油(you)廠，常采用耐硫(liu)(liu)(liu)化(hua)(hua)(hua)氫腐(fu)(fu)蝕(shi)(shi)的(de)(de)鋁箔來保護這(zhe)些容器。

化學腐(fu)蝕比較簡單，而(er)且只在某(mou)些特定條件下才會發(fa)生(sheng)。在生(sheng)產(chan)和日常(chang)(chang)生(sheng)活中普遍存在的(de)(de)、破(po)壞最嚴(yan)重(zhong)的(de)(de)是(shi)電化學腐(fu)蝕，它(ta)是(shi)金屬常(chang)(chang)患的(de)(de)“風濕(shi)病”。

電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)化腐蝕(shi)是指金(jin)(jin)屬與電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)解質溶(rong)液(ye)(ye)作(zuo)用所發(fa)(fa)生的(de)(de)(de)腐蝕(shi)。它的(de)(de)(de)特點是在腐蝕(shi)過程中(zhong)有電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流產生，這是金(jin)(jin)屬表面(mian)發(fa)(fa)生腐蝕(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池作(zuo)用的(de)(de)(de)結果(guo)。通常在電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)化腐蝕(shi)中(zhong)規(gui)定，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位較低的(de)(de)(de)金(jin)(jin)屬為陽極(ji)(ji)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位較高的(de)(de)(de)金(jin)(jin)屬為陰極(ji)(ji)。當兩種(zhong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位不同的(de)(de)(de)金(jin)(jin)屬相接(jie)觸，或同種(zhong)金(jin)(jin)屬的(de)(de)(de)不同的(de)(de)(de)部位具(ju)有不同電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位時，它們侵(qin)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)解質溶(rong)液(ye)(ye)（潮濕氣(qi)體、海水(shui)、酸、堿、鹽的(de)(de)(de)水(shui)溶(rong)液(ye)(ye)或土壤等）后會變形成腐蝕(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池。結果(guo)，作(zuo)為陽極(ji)(ji)的(de)(de)(de)（電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位低的(de)(de)(de)）金(jin)(jin)屬，由于(yu)不斷失去電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)子(zi)(zi)并將自己的(de)(de)(de)離子(zi)(zi)投入(ru)溶(rong)液(ye)(ye)而被(bei)腐蝕(shi)，而作(zuo)為陰極(ji)(ji)的(de)(de)(de)（電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位高的(de)(de)(de)）金(jin)(jin)屬由于(yu)僅起著傳遞電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)子(zi)(zi)的(de)(de)(de)作(zuo)用，本身(shen)沒有發(fa)(fa)生腐蝕(shi)及其(qi)他(ta)變化。