一(yi)塊金(jin)屬(shu)(shu)，表面看來(lai)挺光滑，可(ke)是(shi)在(zai)顯微鏡下就(jiu)會(hui)發現(xian)，它(ta)的(de)(de)結構很不均(jun)勻，這(zhe)就(jiu)為(wei)“病(bing)(bing)從(cong)口(kou)入(ru)(ru)”大(da)開了方(fang)便之門(men)，因(yin)為(wei)金(jin)屬(shu)(shu)遍體都(dou)是(shi)“口(kou)”，準確一(yi)點說，不是(shi)病(bing)(bing)從(cong)口(kou)入(ru)(ru)，而是(shi)病(bing)(bing)從(cong)“皮(pi)”入(ru)(ru)了。所(suo)以金(jin)屬(shu)(shu)的(de)(de)常見(jian)病(bing)(bing)--腐(fu)蝕，一(yi)般都(dou)開始(shi)于“皮(pi)膚病(bing)(bing)”。首(shou)先(xian)是(shi)金(jin)屬(shu)(shu)“皮(pi)膚潰瘍”，然后逐漸侵入(ru)(ru)到內(nei)部。由于金(jin)屬(shu)(shu)接觸的(de)(de)物質多種(zhong)多樣，“得病(bing)(bing)”的(de)(de)條件也各(ge)不相同，所(suo)以金(jin)屬(shu)(shu)的(de)(de)常見(jian)病(bing)(bing)還可(ke)以分為(wei)許(xu)多種(zhong)。也就(jiu)是(shi)說，金(jin)屬(shu)(shu)腐(fu)蝕可(ke)以分為(wei)許(xu)多種(zhong)類。

金(jin)屬腐(fu)蝕(shi)(shi)分(fen)類的(de)(de)(de)方(fang)法很(hen)多，常見(jian)的(de)(de)(de)一(yi)種就是根據腐(fu)蝕(shi)(shi)過程中是否(fou)有電(dian)流產生，分(fen)為化(hua)學(xue)腐(fu)蝕(shi)(shi)和電(dian)化(hua)學(xue)腐(fu)蝕(shi)(shi)兩類。化(hua)學(xue)腐(fu)蝕(shi)(shi)一(yi)般是在干燥(zao)和高溫(wen)的(de)(de)(de)環境下(xia)發生的(de)(de)(de)，它是金(jin)屬的(de)(de)(de)“干熱病”；電(dian)化(hua)學(xue)腐(fu)蝕(shi)(shi)是在潮(chao)濕的(de)(de)(de)環境下(xia)發生的(de)(de)(de)，它是金(jin)屬的(de)(de)(de)“風(feng)濕病”。

 化(hua)學(xue)(xue)腐(fu)蝕是(shi)金(jin)屬(shu)在不導電環境中的腐(fu)蝕，它是(shi)金(jin)屬(shu)與某種物質(zhi)直接(jie)接(jie)觸(chu)時發(fa)生的化(hua)學(xue)(xue)反(fan)應。在化(hua)學(xue)(xue)腐(fu)蝕中，和金(jin)屬(shu)接(jie)觸(chu)發(fa)生反(fan)應的物質(zhi)可(ke)以是(shi)氣體，也可(ke)以是(shi)液體，所(suo)以化(hua)學(xue)(xue)腐(fu)蝕又分(fen)為氣體腐(fu)蝕和液體腐(fu)蝕兩種。

 在(zai)(zai)高溫下(xia)(xia)，或(huo)周(zhou)圍(wei)沒(mei)有(you)導(dao)電物(wu)質(zhi)的(de)(de)條(tiao)件下(xia)(xia)，金(jin)屬(shu)與空氣(qi)或(huo)其他(ta)其他(ta)發(fa)生(sheng)(sheng)反應(ying)，表(biao)面(mian)生(sheng)(sheng)成(cheng)氧化(hua)(hua)(hua)物(wu)或(huo)其他(ta)化(hua)(hua)(hua)合物(wu)的(de)(de)現象，稱為氣(qi)體(ti)腐(fu)蝕。自(zi)然界中(zhong)，氣(qi)體(ti)腐(fu)蝕的(de)(de)現象也是(shi)很(hen)多(duo)。例如，鐵在(zai)(zai)空氣(qi)中(zhong)或(huo)氧氣(qi)中(zhong)加熱時，表(biao)面(mian)會生(sheng)(sheng)成(cheng)鐵的(de)(de)氧化(hua)(hua)(hua)物(wu)膜(mo)；鋁(lv)在(zai)(zai)空氣(qi)中(zhong)會與氧氣(qi)反應(ying)，表(biao)面(mian)生(sheng)(sheng)成(cheng)一層(ceng)氧化(hua)(hua)(hua)鋁(lv)薄膜(mo)。像這樣(yang)，金(jin)屬(shu)與周(zhou)圍(wei)的(de)(de)物(wu)質(zhi)接(jie)觸發(fa)生(sheng)(sheng)反應(ying)生(sheng)(sheng)成(cheng)了(le)化(hua)(hua)(hua)合物(wu)，我們就(jiu)說金(jin)屬(shu)被腐(fu)蝕了(le)，生(sheng)(sheng)成(cheng)的(de)(de)化(hua)(hua)(hua)合物(wu)（膜(mo)）就(jiu)是(shi)腐(fu)蝕的(de)(de)產(chan)物(wu)（常稱作銹）。

金(jin)屬(shu)在(zai)不導電(dian)的(de)液(ye)(ye)體(ti)里的(de)腐(fu)(fu)蝕(shi)(shi)也(ye)(ye)是一(yi)種化(hua)(hua)學腐(fu)(fu)蝕(shi)(shi)，叫做液(ye)(ye)體(ti)腐(fu)(fu)蝕(shi)(shi)。銀可與(yu)碘發生液(ye)(ye)體(ti)腐(fu)(fu)蝕(shi)(shi)。例如(ru)把(ba)碘溶解于(yu)乙(yi)(yi)醚中(zhong)，制成(cheng)(cheng)(cheng)碘的(de)乙(yi)(yi)醚溶液(ye)(ye)。乙(yi)(yi)醚是一(yi)種有(you)機(ji)物(wu)，不能(neng)導電(dian)。把(ba)銀塊投入溶液(ye)(ye)中(zhong)，溶解了的(de)碘能(neng)夠與(yu)銀反應(ying)，在(zai)銀的(de)表面生產(chan)碘化(hua)(hua)銀膜(mo)。石(shi)油(you)中(zhong)往往含(han)有(you)硫(liu)、硫(liu)化(hua)(hua)氫及某些(xie)含(han)硫(liu)的(de)有(you)機(ji)物(wu)，石(shi)油(you)中(zhong)還含(han)有(you)少量水，這少量的(de)水一(yi)般不能(neng)與(yu)硫(liu)的(de)化(hua)(hua)合物(wu)形成(cheng)(cheng)(cheng)導電(dian)溶液(ye)(ye)，但它卻能(neng)加(jia)速(su)硫(liu)的(de)化(hua)(hua)合物(wu)與(yu)金(jin)屬(shu)發生化(hua)(hua)學反應(ying)，成(cheng)(cheng)(cheng)為反應(ying)的(de)催化(hua)(hua)劑。例如(ru)，硫(liu)化(hua)(hua)氫可與(yu)鐵(tie)、鉛、銅、汞、銀等反應(ying)，生成(cheng)(cheng)(cheng)這些(xie)金(jin)屬(shu)的(de)硫(liu)化(hua)(hua)物(wu)，單質硫(liu)也(ye)(ye)可與(yu)銅、汞、銀等金(jin)屬(shu)反應(ying)，所以儲存(cun)石(shi)油(you)的(de)容(rong)(rong)器上部(bu)或蓋子往往被硫(liu)化(hua)(hua)氫腐(fu)(fu)蝕(shi)(shi)。在(zai)煉(lian)油(you)廠，常(chang)采(cai)用耐硫(liu)化(hua)(hua)氫腐(fu)(fu)蝕(shi)(shi)的(de)鋁箔來保護這些(xie)容(rong)(rong)器。

化學腐蝕(shi)比較簡(jian)單，而且只在某些特(te)定條件(jian)下才(cai)會發(fa)生(sheng)。在生(sheng)產和日常(chang)生(sheng)活(huo)中普遍存在的、破壞最嚴重的是電化學腐蝕(shi)，它是金屬常(chang)患的“風濕病”。

電(dian)(dian)(dian)(dian)(dian)(dian)(dian)化(hua)腐(fu)(fu)(fu)蝕(shi)是(shi)指金屬(shu)(shu)(shu)(shu)與(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)解(jie)質溶(rong)液(ye)作(zuo)用(yong)所發(fa)生的(de)(de)(de)(de)腐(fu)(fu)(fu)蝕(shi)。它的(de)(de)(de)(de)特點是(shi)在(zai)(zai)腐(fu)(fu)(fu)蝕(shi)過(guo)程中有(you)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流產生，這是(shi)金屬(shu)(shu)(shu)(shu)表面發(fa)生腐(fu)(fu)(fu)蝕(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)作(zuo)用(yong)的(de)(de)(de)(de)結果。通常在(zai)(zai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)化(hua)腐(fu)(fu)(fu)蝕(shi)中規定(ding)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)較(jiao)(jiao)低的(de)(de)(de)(de)金屬(shu)(shu)(shu)(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)較(jiao)(jiao)高的(de)(de)(de)(de)金屬(shu)(shu)(shu)(shu)為(wei)陰極(ji)。當兩種電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)不同(tong)的(de)(de)(de)(de)金屬(shu)(shu)(shu)(shu)相接觸，或同(tong)種金屬(shu)(shu)(shu)(shu)的(de)(de)(de)(de)不同(tong)的(de)(de)(de)(de)部位(wei)具有(you)不同(tong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)時，它們(men)侵入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)解(jie)質溶(rong)液(ye)（潮濕氣體、海水、酸、堿、鹽的(de)(de)(de)(de)水溶(rong)液(ye)或土壤等(deng)）后會變形成腐(fu)(fu)(fu)蝕(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)。結果，作(zuo)為(wei)陽(yang)極(ji)的(de)(de)(de)(de)（電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)低的(de)(de)(de)(de)）金屬(shu)(shu)(shu)(shu)，由(you)(you)于(yu)不斷失去(qu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)子(zi)(zi)并將自(zi)己的(de)(de)(de)(de)離子(zi)(zi)投入溶(rong)液(ye)而(er)被腐(fu)(fu)(fu)蝕(shi)，而(er)作(zuo)為(wei)陰極(ji)的(de)(de)(de)(de)（電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)高的(de)(de)(de)(de)）金屬(shu)(shu)(shu)(shu)由(you)(you)于(yu)僅起著傳遞電(dian)(dian)(dian)(dian)(dian)(dian)(dian)子(zi)(zi)的(de)(de)(de)(de)作(zuo)用(yong)，本身沒有(you)發(fa)生腐(fu)(fu)(fu)蝕(shi)及其他變化(hua)。