一塊金(jin)屬(shu)(shu)，表面(mian)看來(lai)挺光滑，可是(shi)(shi)在顯(xian)微鏡下(xia)就(jiu)會發(fa)現，它的結構很不均(jun)勻，這就(jiu)為(wei)“病(bing)從口入”大開了方便之門，因為(wei)金(jin)屬(shu)(shu)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(pi)”入了。所(suo)以(yi)金(jin)屬(shu)(shu)的常見病(bing)--腐蝕，一般都開始于(yu)“皮(pi)膚病(bing)”。首先是(shi)(shi)金(jin)屬(shu)(shu)“皮(pi)膚潰瘍”，然后逐漸(jian)侵入到內部(bu)。由于(yu)金(jin)屬(shu)(shu)接觸的物質多種(zhong)多樣，“得病(bing)”的條件也各不相(xiang)同，所(suo)以(yi)金(jin)屬(shu)(shu)的常見病(bing)還可以(yi)分為(wei)許多種(zhong)。也就(jiu)是(shi)(shi)說(shuo)，金(jin)屬(shu)(shu)腐蝕可以(yi)分為(wei)許多種(zhong)類。

金屬(shu)(shu)腐(fu)(fu)蝕(shi)分類的(de)方(fang)法很多，常見的(de)一種就是根(gen)據腐(fu)(fu)蝕(shi)過程中是否有電流產生，分為(wei)化(hua)學(xue)腐(fu)(fu)蝕(shi)和(he)(he)電化(hua)學(xue)腐(fu)(fu)蝕(shi)兩類。化(hua)學(xue)腐(fu)(fu)蝕(shi)一般是在干燥和(he)(he)高(gao)溫的(de)環境(jing)下(xia)(xia)發生的(de)，它是金屬(shu)(shu)的(de)“干熱病”；電化(hua)學(xue)腐(fu)(fu)蝕(shi)是在潮濕的(de)環境(jing)下(xia)(xia)發生的(de)，它是金屬(shu)(shu)的(de)“風濕病”。

 化(hua)(hua)(hua)學腐(fu)(fu)(fu)蝕(shi)是金(jin)屬在不導電環境中(zhong)(zhong)的(de)腐(fu)(fu)(fu)蝕(shi)，它(ta)是金(jin)屬與某種物(wu)質直接(jie)接(jie)觸時發生的(de)化(hua)(hua)(hua)學反應(ying)。在化(hua)(hua)(hua)學腐(fu)(fu)(fu)蝕(shi)中(zhong)(zhong)，和(he)金(jin)屬接(jie)觸發生反應(ying)的(de)物(wu)質可以(yi)(yi)是氣體，也(ye)可以(yi)(yi)是液體，所以(yi)(yi)化(hua)(hua)(hua)學腐(fu)(fu)(fu)蝕(shi)又分為氣體腐(fu)(fu)(fu)蝕(shi)和(he)液體腐(fu)(fu)(fu)蝕(shi)兩(liang)種。

 在高(gao)溫下，或(huo)周圍沒有導電物(wu)(wu)質(zhi)的(de)條件下，金(jin)屬與空氣(qi)(qi)或(huo)其(qi)(qi)他其(qi)(qi)他發生(sheng)(sheng)(sheng)反(fan)(fan)應，表面生(sheng)(sheng)(sheng)成氧(yang)化(hua)物(wu)(wu)或(huo)其(qi)(qi)他化(hua)合(he)物(wu)(wu)的(de)現(xian)象，稱(cheng)為氣(qi)(qi)體(ti)腐(fu)蝕。自然界(jie)中，氣(qi)(qi)體(ti)腐(fu)蝕的(de)現(xian)象也是(shi)很多(duo)。例如，鐵在空氣(qi)(qi)中或(huo)氧(yang)氣(qi)(qi)中加熱時，表面會(hui)生(sheng)(sheng)(sheng)成鐵的(de)氧(yang)化(hua)物(wu)(wu)膜(mo)(mo)；鋁(lv)在空氣(qi)(qi)中會(hui)與氧(yang)氣(qi)(qi)反(fan)(fan)應，表面生(sheng)(sheng)(sheng)成一層氧(yang)化(hua)鋁(lv)薄(bo)膜(mo)(mo)。像(xiang)這樣，金(jin)屬與周圍的(de)物(wu)(wu)質(zhi)接(jie)觸發生(sheng)(sheng)(sheng)反(fan)(fan)應生(sheng)(sheng)(sheng)成了(le)化(hua)合(he)物(wu)(wu)，我(wo)們(men)就(jiu)(jiu)說金(jin)屬被腐(fu)蝕了(le)，生(sheng)(sheng)(sheng)成的(de)化(hua)合(he)物(wu)(wu)（膜(mo)(mo)）就(jiu)(jiu)是(shi)腐(fu)蝕的(de)產物(wu)(wu)（常稱(cheng)作(zuo)銹）。

金(jin)屬在不導電(dian)的(de)(de)(de)液(ye)(ye)(ye)體(ti)(ti)里的(de)(de)(de)腐(fu)蝕(shi)也是(shi)一種化(hua)(hua)(hua)學(xue)腐(fu)蝕(shi)，叫做液(ye)(ye)(ye)體(ti)(ti)腐(fu)蝕(shi)。銀可(ke)與(yu)碘(dian)發生(sheng)液(ye)(ye)(ye)體(ti)(ti)腐(fu)蝕(shi)。例如(ru)把(ba)碘(dian)溶(rong)解于乙(yi)醚(mi)中(zhong)，制成碘(dian)的(de)(de)(de)乙(yi)醚(mi)溶(rong)液(ye)(ye)(ye)。乙(yi)醚(mi)是(shi)一種有(you)(you)機物，不能導電(dian)。把(ba)銀塊(kuai)投入溶(rong)液(ye)(ye)(ye)中(zhong)，溶(rong)解了的(de)(de)(de)碘(dian)能夠與(yu)銀反應(ying)，在銀的(de)(de)(de)表面生(sheng)產(chan)碘(dian)化(hua)(hua)(hua)銀膜(mo)。石(shi)油(you)(you)中(zhong)往往含有(you)(you)硫(liu)(liu)、硫(liu)(liu)化(hua)(hua)(hua)氫(qing)(qing)及某些(xie)含硫(liu)(liu)的(de)(de)(de)有(you)(you)機物，石(shi)油(you)(you)中(zhong)還含有(you)(you)少量水(shui)，這少量的(de)(de)(de)水(shui)一般不能與(yu)硫(liu)(liu)的(de)(de)(de)化(hua)(hua)(hua)合物形成導電(dian)溶(rong)液(ye)(ye)(ye)，但它(ta)卻能加(jia)速(su)硫(liu)(liu)的(de)(de)(de)化(hua)(hua)(hua)合物與(yu)金(jin)屬發生(sheng)化(hua)(hua)(hua)學(xue)反應(ying)，成為反應(ying)的(de)(de)(de)催化(hua)(hua)(hua)劑。例如(ru)，硫(liu)(liu)化(hua)(hua)(hua)氫(qing)(qing)可(ke)與(yu)鐵、鉛、銅、汞、銀等(deng)反應(ying)，生(sheng)成這些(xie)金(jin)屬的(de)(de)(de)硫(liu)(liu)化(hua)(hua)(hua)物，單(dan)質硫(liu)(liu)也可(ke)與(yu)銅、汞、銀等(deng)金(jin)屬反應(ying)，所以儲(chu)存(cun)石(shi)油(you)(you)的(de)(de)(de)容器上部或蓋子往往被硫(liu)(liu)化(hua)(hua)(hua)氫(qing)(qing)腐(fu)蝕(shi)。在煉油(you)(you)廠(chang)，常采用耐(nai)硫(liu)(liu)化(hua)(hua)(hua)氫(qing)(qing)腐(fu)蝕(shi)的(de)(de)(de)鋁箔來(lai)保(bao)護這些(xie)容器。

化(hua)(hua)學(xue)腐蝕比較簡(jian)單(dan)，而(er)且只(zhi)在某些(xie)特定條件下才(cai)會發生。在生產和日常生活中普遍(bian)存在的、破壞最嚴重的是(shi)電(dian)化(hua)(hua)學(xue)腐蝕，它(ta)是(shi)金屬(shu)常患的“風濕病”。

電(dian)(dian)(dian)(dian)(dian)(dian)化腐(fu)(fu)蝕是指金(jin)(jin)屬(shu)(shu)(shu)與(yu)電(dian)(dian)(dian)(dian)(dian)(dian)解(jie)(jie)質(zhi)溶(rong)液作(zuo)(zuo)用(yong)所發生的(de)(de)(de)(de)腐(fu)(fu)蝕。它的(de)(de)(de)(de)特點是在腐(fu)(fu)蝕過(guo)程中有(you)電(dian)(dian)(dian)(dian)(dian)(dian)流產(chan)生，這是金(jin)(jin)屬(shu)(shu)(shu)表(biao)面發生腐(fu)(fu)蝕電(dian)(dian)(dian)(dian)(dian)(dian)池作(zuo)(zuo)用(yong)的(de)(de)(de)(de)結果。通(tong)常在電(dian)(dian)(dian)(dian)(dian)(dian)化腐(fu)(fu)蝕中規定，電(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)(wei)較(jiao)低的(de)(de)(de)(de)金(jin)(jin)屬(shu)(shu)(shu)為(wei)陽(yang)(yang)極(ji)，電(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)(wei)較(jiao)高(gao)的(de)(de)(de)(de)金(jin)(jin)屬(shu)(shu)(shu)為(wei)陰極(ji)。當兩種(zhong)電(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)(wei)不(bu)同(tong)的(de)(de)(de)(de)金(jin)(jin)屬(shu)(shu)(shu)相(xiang)接(jie)觸(chu)，或同(tong)種(zhong)金(jin)(jin)屬(shu)(shu)(shu)的(de)(de)(de)(de)不(bu)同(tong)的(de)(de)(de)(de)部位(wei)(wei)(wei)具有(you)不(bu)同(tong)電(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)(wei)時，它們(men)侵入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)解(jie)(jie)質(zhi)溶(rong)液（潮濕(shi)氣(qi)體、海水、酸、堿、鹽的(de)(de)(de)(de)水溶(rong)液或土壤等）后會變形成腐(fu)(fu)蝕電(dian)(dian)(dian)(dian)(dian)(dian)池。結果，作(zuo)(zuo)為(wei)陽(yang)(yang)極(ji)的(de)(de)(de)(de)（電(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)(wei)低的(de)(de)(de)(de)）金(jin)(jin)屬(shu)(shu)(shu)，由(you)于(yu)不(bu)斷失(shi)去電(dian)(dian)(dian)(dian)(dian)(dian)子(zi)并將自(zi)己的(de)(de)(de)(de)離子(zi)投入(ru)溶(rong)液而(er)被腐(fu)(fu)蝕，而(er)作(zuo)(zuo)為(wei)陰極(ji)的(de)(de)(de)(de)（電(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)(wei)高(gao)的(de)(de)(de)(de)）金(jin)(jin)屬(shu)(shu)(shu)由(you)于(yu)僅起著(zhu)傳遞電(dian)(dian)(dian)(dian)(dian)(dian)子(zi)的(de)(de)(de)(de)作(zuo)(zuo)用(yong)，本身沒(mei)有(you)發生腐(fu)(fu)蝕及其他變化。