一塊金(jin)屬，表面看來挺光(guang)滑(hua)，可(ke)是(shi)在(zai)顯微鏡下就(jiu)會發現，它的結構很不(bu)均勻，這就(jiu)為“病(bing)(bing)從(cong)口入(ru)(ru)(ru)”大開了(le)方便之門，因為金(jin)屬遍體(ti)都是(shi)“口”，準(zhun)確一點(dian)說(shuo)，不(bu)是(shi)病(bing)(bing)從(cong)口入(ru)(ru)(ru)，而(er)是(shi)病(bing)(bing)從(cong)“皮”入(ru)(ru)(ru)了(le)。所(suo)以(yi)金(jin)屬的常見病(bing)(bing)--腐蝕(shi)，一般(ban)都開始于“皮膚(fu)病(bing)(bing)”。首先是(shi)金(jin)屬“皮膚(fu)潰瘍”，然后逐漸侵入(ru)(ru)(ru)到內部。由于金(jin)屬接觸的物質多(duo)(duo)種(zhong)多(duo)(duo)樣，“得(de)病(bing)(bing)”的條件也各(ge)不(bu)相(xiang)同(tong)，所(suo)以(yi)金(jin)屬的常見病(bing)(bing)還(huan)可(ke)以(yi)分為許多(duo)(duo)種(zhong)。也就(jiu)是(shi)說(shuo)，金(jin)屬腐蝕(shi)可(ke)以(yi)分為許多(duo)(duo)種(zhong)類。

金屬腐(fu)(fu)(fu)蝕(shi)分類的方法很多，常見的一種就(jiu)是(shi)根據(ju)腐(fu)(fu)(fu)蝕(shi)過(guo)程中是(shi)否有電(dian)流產生(sheng)，分為化(hua)學腐(fu)(fu)(fu)蝕(shi)和(he)(he)電(dian)化(hua)學腐(fu)(fu)(fu)蝕(shi)兩類。化(hua)學腐(fu)(fu)(fu)蝕(shi)一般是(shi)在干(gan)燥和(he)(he)高(gao)溫的環(huan)(huan)境(jing)下發(fa)生(sheng)的，它是(shi)金屬的“干(gan)熱病”；電(dian)化(hua)學腐(fu)(fu)(fu)蝕(shi)是(shi)在潮濕的環(huan)(huan)境(jing)下發(fa)生(sheng)的，它是(shi)金屬的“風(feng)濕病”。

 化(hua)(hua)學(xue)腐蝕(shi)(shi)是金(jin)(jin)屬(shu)在不導電(dian)環境中的腐蝕(shi)(shi)，它是金(jin)(jin)屬(shu)與(yu)某種(zhong)物質直接接觸時(shi)發(fa)生的化(hua)(hua)學(xue)反應(ying)。在化(hua)(hua)學(xue)腐蝕(shi)(shi)中，和金(jin)(jin)屬(shu)接觸發(fa)生反應(ying)的物質可以(yi)是氣(qi)體(ti)，也可以(yi)是液體(ti)，所以(yi)化(hua)(hua)學(xue)腐蝕(shi)(shi)又(you)分(fen)為氣(qi)體(ti)腐蝕(shi)(shi)和液體(ti)腐蝕(shi)(shi)兩種(zhong)。

 在(zai)(zai)高溫下，或周圍(wei)沒有導電物(wu)質的(de)(de)條件下，金(jin)屬與(yu)空(kong)(kong)氣(qi)(qi)(qi)或其(qi)他(ta)其(qi)他(ta)發生(sheng)(sheng)反(fan)應，表面(mian)生(sheng)(sheng)成(cheng)氧(yang)(yang)化物(wu)或其(qi)他(ta)化合(he)物(wu)的(de)(de)現象(xiang)，稱(cheng)為氣(qi)(qi)(qi)體腐(fu)(fu)蝕。自(zi)然界中，氣(qi)(qi)(qi)體腐(fu)(fu)蝕的(de)(de)現象(xiang)也是很多。例(li)如，鐵在(zai)(zai)空(kong)(kong)氣(qi)(qi)(qi)中或氧(yang)(yang)氣(qi)(qi)(qi)中加熱時，表面(mian)會生(sheng)(sheng)成(cheng)鐵的(de)(de)氧(yang)(yang)化物(wu)膜(mo)；鋁在(zai)(zai)空(kong)(kong)氣(qi)(qi)(qi)中會與(yu)氧(yang)(yang)氣(qi)(qi)(qi)反(fan)應，表面(mian)生(sheng)(sheng)成(cheng)一層氧(yang)(yang)化鋁薄膜(mo)。像這樣，金(jin)屬與(yu)周圍(wei)的(de)(de)物(wu)質接觸(chu)發生(sheng)(sheng)反(fan)應生(sheng)(sheng)成(cheng)了化合(he)物(wu)，我們就說金(jin)屬被腐(fu)(fu)蝕了，生(sheng)(sheng)成(cheng)的(de)(de)化合(he)物(wu)（膜(mo)）就是腐(fu)(fu)蝕的(de)(de)產(chan)物(wu)（常(chang)稱(cheng)作銹）。

金(jin)(jin)屬(shu)在(zai)(zai)(zai)不(bu)(bu)導電的(de)(de)(de)(de)液(ye)體里的(de)(de)(de)(de)腐蝕(shi)也(ye)是一種化(hua)學(xue)腐蝕(shi)，叫做(zuo)液(ye)體腐蝕(shi)。銀(yin)(yin)可與(yu)(yu)碘發生(sheng)(sheng)液(ye)體腐蝕(shi)。例如(ru)把(ba)碘溶解(jie)于乙(yi)(yi)醚(mi)(mi)中，制成碘的(de)(de)(de)(de)乙(yi)(yi)醚(mi)(mi)溶液(ye)。乙(yi)(yi)醚(mi)(mi)是一種有(you)(you)機(ji)物，不(bu)(bu)能(neng)(neng)導電。把(ba)銀(yin)(yin)塊投入溶液(ye)中，溶解(jie)了(le)的(de)(de)(de)(de)碘能(neng)(neng)夠與(yu)(yu)銀(yin)(yin)反應(ying)，在(zai)(zai)(zai)銀(yin)(yin)的(de)(de)(de)(de)表面生(sheng)(sheng)產(chan)碘化(hua)銀(yin)(yin)膜。石油(you)中往往含(han)有(you)(you)硫(liu)(liu)、硫(liu)(liu)化(hua)氫及(ji)某(mou)些(xie)(xie)含(han)硫(liu)(liu)的(de)(de)(de)(de)有(you)(you)機(ji)物，石油(you)中還含(han)有(you)(you)少量水，這(zhe)少量的(de)(de)(de)(de)水一般(ban)不(bu)(bu)能(neng)(neng)與(yu)(yu)硫(liu)(liu)的(de)(de)(de)(de)化(hua)合物形成導電溶液(ye)，但它卻能(neng)(neng)加(jia)速硫(liu)(liu)的(de)(de)(de)(de)化(hua)合物與(yu)(yu)金(jin)(jin)屬(shu)發生(sheng)(sheng)化(hua)學(xue)反應(ying)，成為反應(ying)的(de)(de)(de)(de)催化(hua)劑。例如(ru)，硫(liu)(liu)化(hua)氫可與(yu)(yu)鐵、鉛、銅、汞(gong)、銀(yin)(yin)等反應(ying)，生(sheng)(sheng)成這(zhe)些(xie)(xie)金(jin)(jin)屬(shu)的(de)(de)(de)(de)硫(liu)(liu)化(hua)物，單質硫(liu)(liu)也(ye)可與(yu)(yu)銅、汞(gong)、銀(yin)(yin)等金(jin)(jin)屬(shu)反應(ying)，所以儲存(cun)石油(you)的(de)(de)(de)(de)容器上(shang)部或(huo)蓋(gai)子(zi)往往被硫(liu)(liu)化(hua)氫腐蝕(shi)。在(zai)(zai)(zai)煉(lian)油(you)廠，常采(cai)用(yong)耐硫(liu)(liu)化(hua)氫腐蝕(shi)的(de)(de)(de)(de)鋁箔來保護這(zhe)些(xie)(xie)容器。

化(hua)學(xue)腐蝕(shi)比(bi)較簡單，而且只在某些特定條件下才會發生。在生產和日常(chang)生活(huo)中(zhong)普遍存(cun)在的、破壞(huai)最嚴重(zhong)的是電(dian)化(hua)學(xue)腐蝕(shi)，它是金屬常(chang)患(huan)的“風(feng)濕病(bing)”。

電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)化(hua)腐(fu)(fu)(fu)蝕(shi)(shi)是(shi)指金(jin)(jin)屬(shu)(shu)與電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)解質溶液作(zuo)(zuo)用所發生的(de)(de)腐(fu)(fu)(fu)蝕(shi)(shi)。它的(de)(de)特點是(shi)在(zai)腐(fu)(fu)(fu)蝕(shi)(shi)過程中(zhong)有(you)(you)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流產生，這是(shi)金(jin)(jin)屬(shu)(shu)表面發生腐(fu)(fu)(fu)蝕(shi)(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池作(zuo)(zuo)用的(de)(de)結果。通常在(zai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)化(hua)腐(fu)(fu)(fu)蝕(shi)(shi)中(zhong)規定(ding)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)較(jiao)低(di)的(de)(de)金(jin)(jin)屬(shu)(shu)為(wei)陽極(ji)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)較(jiao)高(gao)的(de)(de)金(jin)(jin)屬(shu)(shu)為(wei)陰極(ji)。當兩種電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)不(bu)同的(de)(de)金(jin)(jin)屬(shu)(shu)相接觸，或同種金(jin)(jin)屬(shu)(shu)的(de)(de)不(bu)同的(de)(de)部(bu)位(wei)(wei)具(ju)有(you)(you)不(bu)同電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)時，它們侵入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)解質溶液（潮濕氣體、海水、酸、堿、鹽(yan)的(de)(de)水溶液或土壤等）后會變形(xing)成腐(fu)(fu)(fu)蝕(shi)(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池。結果，作(zuo)(zuo)為(wei)陽極(ji)的(de)(de)（電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)低(di)的(de)(de)）金(jin)(jin)屬(shu)(shu)，由(you)(you)于不(bu)斷失(shi)去(qu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)子并將自己的(de)(de)離(li)子投入(ru)(ru)溶液而(er)被腐(fu)(fu)(fu)蝕(shi)(shi)，而(er)作(zuo)(zuo)為(wei)陰極(ji)的(de)(de)（電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)高(gao)的(de)(de)）金(jin)(jin)屬(shu)(shu)由(you)(you)于僅起著傳遞電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)子的(de)(de)作(zuo)(zuo)用，本身沒有(you)(you)發生腐(fu)(fu)(fu)蝕(shi)(shi)及其他(ta)變化(hua)。