一(yi)塊金(jin)(jin)(jin)屬(shu)，表面看來挺光滑(hua)，可(ke)(ke)是(shi)(shi)在顯微鏡下(xia)就(jiu)(jiu)會(hui)發現，它的結構很不均勻，這(zhe)就(jiu)(jiu)為“病(bing)(bing)從(cong)口(kou)入(ru)(ru)(ru)”大(da)開了方(fang)便(bian)之門，因為金(jin)(jin)(jin)屬(shu)遍體都是(shi)(shi)“口(kou)”，準確一(yi)點說，不是(shi)(shi)病(bing)(bing)從(cong)口(kou)入(ru)(ru)(ru)，而是(shi)(shi)病(bing)(bing)從(cong)“皮(pi)”入(ru)(ru)(ru)了。所(suo)以(yi)金(jin)(jin)(jin)屬(shu)的常見病(bing)(bing)--腐(fu)蝕(shi)，一(yi)般都開始于(yu)“皮(pi)膚病(bing)(bing)”。首先是(shi)(shi)金(jin)(jin)(jin)屬(shu)“皮(pi)膚潰瘍”，然后(hou)逐(zhu)漸侵入(ru)(ru)(ru)到(dao)內部。由(you)于(yu)金(jin)(jin)(jin)屬(shu)接觸(chu)的物質多(duo)種(zhong)多(duo)樣，“得病(bing)(bing)”的條件也(ye)各不相同，所(suo)以(yi)金(jin)(jin)(jin)屬(shu)的常見病(bing)(bing)還可(ke)(ke)以(yi)分為許多(duo)種(zhong)。也(ye)就(jiu)(jiu)是(shi)(shi)說，金(jin)(jin)(jin)屬(shu)腐(fu)蝕(shi)可(ke)(ke)以(yi)分為許多(duo)種(zhong)類。

金(jin)屬(shu)(shu)腐(fu)蝕(shi)(shi)(shi)(shi)分類的(de)方(fang)法很(hen)多，常見的(de)一種就是(shi)(shi)(shi)根據腐(fu)蝕(shi)(shi)(shi)(shi)過程中是(shi)(shi)(shi)否有電(dian)流(liu)產生(sheng)，分為化(hua)學(xue)(xue)腐(fu)蝕(shi)(shi)(shi)(shi)和(he)電(dian)化(hua)學(xue)(xue)腐(fu)蝕(shi)(shi)(shi)(shi)兩(liang)類。化(hua)學(xue)(xue)腐(fu)蝕(shi)(shi)(shi)(shi)一般是(shi)(shi)(shi)在(zai)(zai)干燥和(he)高溫的(de)環(huan)境下(xia)發生(sheng)的(de)，它是(shi)(shi)(shi)金(jin)屬(shu)(shu)的(de)“干熱(re)病”；電(dian)化(hua)學(xue)(xue)腐(fu)蝕(shi)(shi)(shi)(shi)是(shi)(shi)(shi)在(zai)(zai)潮濕(shi)的(de)環(huan)境下(xia)發生(sheng)的(de)，它是(shi)(shi)(shi)金(jin)屬(shu)(shu)的(de)“風濕(shi)病”。

 化學(xue)腐蝕(shi)是(shi)(shi)金(jin)屬(shu)在不導電環境中的(de)腐蝕(shi)，它是(shi)(shi)金(jin)屬(shu)與某種(zhong)物質(zhi)直接接觸(chu)時發生(sheng)的(de)化學(xue)反(fan)應。在化學(xue)腐蝕(shi)中，和金(jin)屬(shu)接觸(chu)發生(sheng)反(fan)應的(de)物質(zhi)可(ke)(ke)以是(shi)(shi)氣體，也(ye)可(ke)(ke)以是(shi)(shi)液體，所以化學(xue)腐蝕(shi)又分(fen)為氣體腐蝕(shi)和液體腐蝕(shi)兩種(zhong)。

 在(zai)(zai)高溫下(xia)，或(huo)周圍(wei)沒(mei)有導電(dian)物(wu)(wu)質(zhi)的(de)條件下(xia)，金(jin)屬(shu)(shu)與(yu)(yu)空氣(qi)或(huo)其(qi)他(ta)(ta)其(qi)他(ta)(ta)發(fa)生反應，表面生成(cheng)氧(yang)(yang)化物(wu)(wu)或(huo)其(qi)他(ta)(ta)化合(he)(he)物(wu)(wu)的(de)現(xian)象(xiang)，稱為氣(qi)體腐(fu)蝕(shi)。自然界中，氣(qi)體腐(fu)蝕(shi)的(de)現(xian)象(xiang)也是很多(duo)。例如，鐵在(zai)(zai)空氣(qi)中或(huo)氧(yang)(yang)氣(qi)中加熱時，表面會(hui)(hui)生成(cheng)鐵的(de)氧(yang)(yang)化物(wu)(wu)膜；鋁(lv)在(zai)(zai)空氣(qi)中會(hui)(hui)與(yu)(yu)氧(yang)(yang)氣(qi)反應，表面生成(cheng)一層氧(yang)(yang)化鋁(lv)薄(bo)膜。像這樣，金(jin)屬(shu)(shu)與(yu)(yu)周圍(wei)的(de)物(wu)(wu)質(zhi)接觸發(fa)生反應生成(cheng)了(le)化合(he)(he)物(wu)(wu)，我們就(jiu)說(shuo)金(jin)屬(shu)(shu)被腐(fu)蝕(shi)了(le)，生成(cheng)的(de)化合(he)(he)物(wu)(wu)（膜）就(jiu)是腐(fu)蝕(shi)的(de)產物(wu)(wu)（常稱作銹）。

金屬在(zai)(zai)不(bu)導電的(de)液(ye)(ye)體里的(de)腐蝕也是(shi)(shi)一種化(hua)(hua)(hua)學(xue)腐蝕，叫做液(ye)(ye)體腐蝕。銀(yin)(yin)可(ke)與(yu)碘發(fa)生(sheng)(sheng)液(ye)(ye)體腐蝕。例(li)如把碘溶解于乙(yi)醚中，制成碘的(de)乙(yi)醚溶液(ye)(ye)。乙(yi)醚是(shi)(shi)一種有機(ji)物(wu)(wu)，不(bu)能導電。把銀(yin)(yin)塊投入溶液(ye)(ye)中，溶解了的(de)碘能夠與(yu)銀(yin)(yin)反應(ying)，在(zai)(zai)銀(yin)(yin)的(de)表面生(sheng)(sheng)產碘化(hua)(hua)(hua)銀(yin)(yin)膜。石(shi)(shi)油中往(wang)往(wang)含(han)有硫(liu)、硫(liu)化(hua)(hua)(hua)氫(qing)及某些(xie)含(han)硫(liu)的(de)有機(ji)物(wu)(wu)，石(shi)(shi)油中還含(han)有少量(liang)水(shui)(shui)，這少量(liang)的(de)水(shui)(shui)一般不(bu)能與(yu)硫(liu)的(de)化(hua)(hua)(hua)合(he)物(wu)(wu)形(xing)成導電溶液(ye)(ye)，但(dan)它卻能加速硫(liu)的(de)化(hua)(hua)(hua)合(he)物(wu)(wu)與(yu)金屬發(fa)生(sheng)(sheng)化(hua)(hua)(hua)學(xue)反應(ying)，成為反應(ying)的(de)催化(hua)(hua)(hua)劑。例(li)如，硫(liu)化(hua)(hua)(hua)氫(qing)可(ke)與(yu)鐵、鉛、銅(tong)、汞、銀(yin)(yin)等反應(ying)，生(sheng)(sheng)成這些(xie)金屬的(de)硫(liu)化(hua)(hua)(hua)物(wu)(wu)，單(dan)質硫(liu)也可(ke)與(yu)銅(tong)、汞、銀(yin)(yin)等金屬反應(ying)，所以儲(chu)存(cun)石(shi)(shi)油的(de)容(rong)器(qi)上部或蓋子(zi)往(wang)往(wang)被(bei)硫(liu)化(hua)(hua)(hua)氫(qing)腐蝕。在(zai)(zai)煉油廠，常采用耐硫(liu)化(hua)(hua)(hua)氫(qing)腐蝕的(de)鋁箔(bo)來保護這些(xie)容(rong)器(qi)。

化學腐蝕(shi)(shi)比較簡單(dan)，而且只在(zai)(zai)某些(xie)特定條件下(xia)才會(hui)發生(sheng)。在(zai)(zai)生(sheng)產和(he)日常(chang)生(sheng)活中普遍(bian)存(cun)在(zai)(zai)的、破壞最嚴重的是電化學腐蝕(shi)(shi)，它是金(jin)屬常(chang)患的“風濕病”。

電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)化腐(fu)蝕(shi)是指金(jin)(jin)屬(shu)與電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)解質溶(rong)液(ye)作(zuo)(zuo)用所發生的(de)腐(fu)蝕(shi)。它(ta)的(de)特點是在(zai)腐(fu)蝕(shi)過程中(zhong)有電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流產生，這是金(jin)(jin)屬(shu)表面發生腐(fu)蝕(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池作(zuo)(zuo)用的(de)結果。通常(chang)在(zai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)化腐(fu)蝕(shi)中(zhong)規定，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)較(jiao)低的(de)金(jin)(jin)屬(shu)為陽(yang)(yang)極(ji)(ji)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)較(jiao)高的(de)金(jin)(jin)屬(shu)為陰(yin)極(ji)(ji)。當兩種電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)不(bu)同的(de)金(jin)(jin)屬(shu)相接觸，或同種金(jin)(jin)屬(shu)的(de)不(bu)同的(de)部位(wei)(wei)具(ju)有不(bu)同電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)時(shi)，它(ta)們侵入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)解質溶(rong)液(ye)（潮濕氣體、海(hai)水、酸(suan)、堿、鹽的(de)水溶(rong)液(ye)或土壤(rang)等）后會變(bian)形成(cheng)腐(fu)蝕(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池。結果，作(zuo)(zuo)為陽(yang)(yang)極(ji)(ji)的(de)（電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)低的(de)）金(jin)(jin)屬(shu)，由于(yu)不(bu)斷失去電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)子(zi)并將(jiang)自(zi)己的(de)離(li)子(zi)投(tou)入溶(rong)液(ye)而(er)(er)被腐(fu)蝕(shi)，而(er)(er)作(zuo)(zuo)為陰(yin)極(ji)(ji)的(de)（電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)(wei)高的(de)）金(jin)(jin)屬(shu)由于(yu)僅(jin)起著傳遞電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)子(zi)的(de)作(zuo)(zuo)用，本身沒有發生腐(fu)蝕(shi)及其他變(bian)化。