一塊(kuai)金(jin)(jin)屬，表(biao)面看來(lai)挺光滑，可是(shi)(shi)在顯微鏡下就(jiu)會發現，它的(de)(de)結構很不均勻，這就(jiu)為“病(bing)從口入”大開(kai)了(le)方(fang)便之門，因為金(jin)(jin)屬遍體都是(shi)(shi)“口”，準確一點說(shuo)，不是(shi)(shi)病(bing)從口入，而是(shi)(shi)病(bing)從“皮”入了(le)。所(suo)以金(jin)(jin)屬的(de)(de)常見病(bing)--腐(fu)蝕(shi)，一般(ban)都開(kai)始于“皮膚(fu)病(bing)”。首先(xian)是(shi)(shi)金(jin)(jin)屬“皮膚(fu)潰瘍(yang)”，然(ran)后逐漸侵入到內(nei)部。由(you)于金(jin)(jin)屬接觸的(de)(de)物(wu)質多(duo)種多(duo)樣，“得病(bing)”的(de)(de)條(tiao)件也各不相(xiang)同，所(suo)以金(jin)(jin)屬的(de)(de)常見病(bing)還可以分(fen)為許多(duo)種。也就(jiu)是(shi)(shi)說(shuo)，金(jin)(jin)屬腐(fu)蝕(shi)可以分(fen)為許多(duo)種類。

金屬腐蝕分(fen)類的(de)方(fang)法很(hen)多，常見的(de)一種就是(shi)根據腐蝕過(guo)程中是(shi)否有電(dian)流產生(sheng)，分(fen)為(wei)化(hua)學(xue)腐蝕和電(dian)化(hua)學(xue)腐蝕兩類。化(hua)學(xue)腐蝕一般是(shi)在(zai)干(gan)燥(zao)和高(gao)溫(wen)的(de)環境(jing)下(xia)發生(sheng)的(de)，它是(shi)金屬的(de)“干(gan)熱病”；電(dian)化(hua)學(xue)腐蝕是(shi)在(zai)潮濕的(de)環境(jing)下(xia)發生(sheng)的(de)，它是(shi)金屬的(de)“風(feng)濕病”。

 化學(xue)腐(fu)(fu)蝕(shi)是(shi)金(jin)屬(shu)(shu)在不導(dao)電環境中的(de)腐(fu)(fu)蝕(shi)，它是(shi)金(jin)屬(shu)(shu)與(yu)某(mou)種物(wu)質直接接觸(chu)時(shi)發(fa)生的(de)化學(xue)反(fan)應。在化學(xue)腐(fu)(fu)蝕(shi)中，和(he)(he)金(jin)屬(shu)(shu)接觸(chu)發(fa)生反(fan)應的(de)物(wu)質可以是(shi)氣體，也可以是(shi)液(ye)體，所以化學(xue)腐(fu)(fu)蝕(shi)又分為氣體腐(fu)(fu)蝕(shi)和(he)(he)液(ye)體腐(fu)(fu)蝕(shi)兩種。

 在高溫下(xia)，或(huo)周(zhou)圍(wei)沒有導電物質的(de)(de)條件下(xia)，金屬與空(kong)氣(qi)(qi)或(huo)其(qi)(qi)他其(qi)(qi)他發生(sheng)反應，表(biao)面生(sheng)成氧化物或(huo)其(qi)(qi)他化合物的(de)(de)現象(xiang)，稱為氣(qi)(qi)體腐(fu)蝕。自然界中(zhong)(zhong)(zhong)，氣(qi)(qi)體腐(fu)蝕的(de)(de)現象(xiang)也(ye)是很(hen)多。例(li)如，鐵在空(kong)氣(qi)(qi)中(zhong)(zhong)(zhong)或(huo)氧氣(qi)(qi)中(zhong)(zhong)(zhong)加熱(re)時，表(biao)面會(hui)生(sheng)成鐵的(de)(de)氧化物膜；鋁在空(kong)氣(qi)(qi)中(zhong)(zhong)(zhong)會(hui)與氧氣(qi)(qi)反應，表(biao)面生(sheng)成一層氧化鋁薄膜。像這樣(yang)，金屬與周(zhou)圍(wei)的(de)(de)物質接觸發生(sheng)反應生(sheng)成了(le)化合物，我(wo)們(men)就說金屬被腐(fu)蝕了(le)，生(sheng)成的(de)(de)化合物（膜）就是腐(fu)蝕的(de)(de)產物（常稱作銹）。

金(jin)屬在(zai)不導(dao)電(dian)的(de)液(ye)體(ti)里(li)的(de)腐蝕(shi)也(ye)是一種(zhong)化(hua)(hua)學腐蝕(shi)，叫做液(ye)體(ti)腐蝕(shi)。銀可與(yu)碘(dian)發(fa)生液(ye)體(ti)腐蝕(shi)。例如(ru)把(ba)碘(dian)溶解于乙(yi)醚(mi)中(zhong)，制成(cheng)碘(dian)的(de)乙(yi)醚(mi)溶液(ye)。乙(yi)醚(mi)是一種(zhong)有(you)機(ji)(ji)物(wu)(wu)，不能導(dao)電(dian)。把(ba)銀塊投(tou)入溶液(ye)中(zhong)，溶解了的(de)碘(dian)能夠與(yu)銀反應(ying)(ying)，在(zai)銀的(de)表(biao)面生產碘(dian)化(hua)(hua)銀膜。石(shi)(shi)油(you)中(zhong)往往含有(you)硫(liu)(liu)(liu)、硫(liu)(liu)(liu)化(hua)(hua)氫及某些(xie)(xie)含硫(liu)(liu)(liu)的(de)有(you)機(ji)(ji)物(wu)(wu)，石(shi)(shi)油(you)中(zhong)還(huan)含有(you)少(shao)量水，這少(shao)量的(de)水一般不能與(yu)硫(liu)(liu)(liu)的(de)化(hua)(hua)合物(wu)(wu)形成(cheng)導(dao)電(dian)溶液(ye)，但它卻能加速硫(liu)(liu)(liu)的(de)化(hua)(hua)合物(wu)(wu)與(yu)金(jin)屬發(fa)生化(hua)(hua)學反應(ying)(ying)，成(cheng)為反應(ying)(ying)的(de)催(cui)化(hua)(hua)劑。例如(ru)，硫(liu)(liu)(liu)化(hua)(hua)氫可與(yu)鐵、鉛、銅、汞(gong)、銀等反應(ying)(ying)，生成(cheng)這些(xie)(xie)金(jin)屬的(de)硫(liu)(liu)(liu)化(hua)(hua)物(wu)(wu)，單質硫(liu)(liu)(liu)也(ye)可與(yu)銅、汞(gong)、銀等金(jin)屬反應(ying)(ying)，所以儲(chu)存石(shi)(shi)油(you)的(de)容(rong)器(qi)上(shang)部(bu)或蓋子往往被硫(liu)(liu)(liu)化(hua)(hua)氫腐蝕(shi)。在(zai)煉油(you)廠，常采(cai)用耐硫(liu)(liu)(liu)化(hua)(hua)氫腐蝕(shi)的(de)鋁箔來保護這些(xie)(xie)容(rong)器(qi)。

化學腐蝕(shi)比較簡單，而且只在(zai)某些特(te)定條件下才會發(fa)生。在(zai)生產和日常生活中(zhong)普遍存在(zai)的(de)、破壞最嚴重的(de)是電化學腐蝕(shi)，它是金(jin)屬(shu)常患的(de)“風濕(shi)病”。

電(dian)(dian)(dian)(dian)(dian)(dian)(dian)化腐(fu)蝕(shi)是指金(jin)屬(shu)與電(dian)(dian)(dian)(dian)(dian)(dian)(dian)解質溶液(ye)作(zuo)用所(suo)發(fa)生(sheng)的(de)(de)(de)腐(fu)蝕(shi)。它(ta)(ta)的(de)(de)(de)特點是在(zai)腐(fu)蝕(shi)過程中有(you)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流產生(sheng)，這是金(jin)屬(shu)表面發(fa)生(sheng)腐(fu)蝕(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池作(zuo)用的(de)(de)(de)結果。通(tong)常在(zai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)化腐(fu)蝕(shi)中規定，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)較(jiao)(jiao)低的(de)(de)(de)金(jin)屬(shu)為(wei)陽(yang)極(ji)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)較(jiao)(jiao)高(gao)的(de)(de)(de)金(jin)屬(shu)為(wei)陰極(ji)。當兩(liang)種(zhong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)不(bu)同的(de)(de)(de)金(jin)屬(shu)相接觸(chu)，或同種(zhong)金(jin)屬(shu)的(de)(de)(de)不(bu)同的(de)(de)(de)部位(wei)(wei)具有(you)不(bu)同電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)時(shi)，它(ta)(ta)們侵入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)解質溶液(ye)（潮濕氣體、海(hai)水(shui)、酸(suan)、堿、鹽(yan)的(de)(de)(de)水(shui)溶液(ye)或土壤等）后會變(bian)形成腐(fu)蝕(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池。結果，作(zuo)為(wei)陽(yang)極(ji)的(de)(de)(de)（電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)低的(de)(de)(de)）金(jin)屬(shu)，由(you)于(yu)(yu)不(bu)斷失去電(dian)(dian)(dian)(dian)(dian)(dian)(dian)子并將自己的(de)(de)(de)離子投(tou)入溶液(ye)而被腐(fu)蝕(shi)，而作(zuo)為(wei)陰極(ji)的(de)(de)(de)（電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)高(gao)的(de)(de)(de)）金(jin)屬(shu)由(you)于(yu)(yu)僅起著傳遞電(dian)(dian)(dian)(dian)(dian)(dian)(dian)子的(de)(de)(de)作(zuo)用，本身沒有(you)發(fa)生(sheng)腐(fu)蝕(shi)及(ji)其他變(bian)化。