一塊金(jin)屬(shu)(shu)(shu)(shu)，表面看來(lai)挺光滑，可是(shi)(shi)在顯(xian)微鏡(jing)下(xia)就(jiu)(jiu)會(hui)發(fa)現，它的結(jie)構很不均勻，這就(jiu)(jiu)為“病(bing)(bing)從(cong)口入”大(da)開了方(fang)便之門，因為金(jin)屬(shu)(shu)(shu)(shu)遍體都是(shi)(shi)“口”，準確一點說，不是(shi)(shi)病(bing)(bing)從(cong)口入，而是(shi)(shi)病(bing)(bing)從(cong)“皮”入了。所(suo)以金(jin)屬(shu)(shu)(shu)(shu)的常(chang)見(jian)病(bing)(bing)--腐(fu)蝕(shi)，一般都開始于“皮膚(fu)病(bing)(bing)”。首(shou)先(xian)是(shi)(shi)金(jin)屬(shu)(shu)(shu)(shu)“皮膚(fu)潰(kui)瘍”，然后逐漸侵入到內部。由于金(jin)屬(shu)(shu)(shu)(shu)接(jie)觸的物質(zhi)多種多樣，“得病(bing)(bing)”的條件也各不相(xiang)同，所(suo)以金(jin)屬(shu)(shu)(shu)(shu)的常(chang)見(jian)病(bing)(bing)還可以分為許多種。也就(jiu)(jiu)是(shi)(shi)說，金(jin)屬(shu)(shu)(shu)(shu)腐(fu)蝕(shi)可以分為許多種類。

金屬腐(fu)蝕(shi)(shi)分類(lei)(lei)的(de)方(fang)法很多(duo)，常見的(de)一(yi)種就是(shi)(shi)根據腐(fu)蝕(shi)(shi)過程(cheng)中(zhong)是(shi)(shi)否有電(dian)流產生(sheng)，分為化(hua)學腐(fu)蝕(shi)(shi)和電(dian)化(hua)學腐(fu)蝕(shi)(shi)兩類(lei)(lei)。化(hua)學腐(fu)蝕(shi)(shi)一(yi)般是(shi)(shi)在(zai)干燥和高溫的(de)環(huan)境下(xia)發生(sheng)的(de)，它是(shi)(shi)金屬的(de)“干熱(re)病”；電(dian)化(hua)學腐(fu)蝕(shi)(shi)是(shi)(shi)在(zai)潮濕(shi)的(de)環(huan)境下(xia)發生(sheng)的(de)，它是(shi)(shi)金屬的(de)“風濕(shi)病”。

 化學腐蝕(shi)是(shi)金(jin)屬在不導電環境中的(de)腐蝕(shi)，它是(shi)金(jin)屬與(yu)某種物質直接(jie)接(jie)觸時發生(sheng)(sheng)的(de)化學反(fan)應(ying)。在化學腐蝕(shi)中，和金(jin)屬接(jie)觸發生(sheng)(sheng)反(fan)應(ying)的(de)物質可以(yi)(yi)是(shi)氣體(ti)(ti)，也可以(yi)(yi)是(shi)液體(ti)(ti)，所以(yi)(yi)化學腐蝕(shi)又分為氣體(ti)(ti)腐蝕(shi)和液體(ti)(ti)腐蝕(shi)兩種。

 在(zai)高(gao)溫下(xia)，或(huo)周圍(wei)沒有導電物(wu)(wu)質(zhi)的條件下(xia)，金(jin)屬(shu)(shu)與(yu)(yu)空氣(qi)或(huo)其他其他發生(sheng)(sheng)(sheng)反應，表(biao)(biao)面(mian)生(sheng)(sheng)(sheng)成氧(yang)(yang)(yang)化(hua)(hua)物(wu)(wu)或(huo)其他化(hua)(hua)合物(wu)(wu)的現象(xiang)，稱(cheng)為氣(qi)體腐蝕(shi)。自(zi)然界中(zhong)，氣(qi)體腐蝕(shi)的現象(xiang)也是很(hen)多。例(li)如，鐵在(zai)空氣(qi)中(zhong)或(huo)氧(yang)(yang)(yang)氣(qi)中(zhong)加熱時，表(biao)(biao)面(mian)會生(sheng)(sheng)(sheng)成鐵的氧(yang)(yang)(yang)化(hua)(hua)物(wu)(wu)膜(mo)；鋁(lv)在(zai)空氣(qi)中(zhong)會與(yu)(yu)氧(yang)(yang)(yang)氣(qi)反應，表(biao)(biao)面(mian)生(sheng)(sheng)(sheng)成一層氧(yang)(yang)(yang)化(hua)(hua)鋁(lv)薄膜(mo)。像這樣，金(jin)屬(shu)(shu)與(yu)(yu)周圍(wei)的物(wu)(wu)質(zhi)接觸發生(sheng)(sheng)(sheng)反應生(sheng)(sheng)(sheng)成了化(hua)(hua)合物(wu)(wu)，我們(men)就說(shuo)金(jin)屬(shu)(shu)被(bei)腐蝕(shi)了，生(sheng)(sheng)(sheng)成的化(hua)(hua)合物(wu)(wu)（膜(mo)）就是腐蝕(shi)的產物(wu)(wu)（常稱(cheng)作(zuo)銹）。

金屬(shu)在(zai)不導電的(de)液(ye)體(ti)里(li)的(de)腐蝕(shi)(shi)也是一種化(hua)(hua)學(xue)腐蝕(shi)(shi)，叫(jiao)做液(ye)體(ti)腐蝕(shi)(shi)。銀可(ke)與(yu)碘(dian)發生(sheng)(sheng)液(ye)體(ti)腐蝕(shi)(shi)。例如把(ba)碘(dian)溶(rong)(rong)(rong)解于乙(yi)醚中(zhong)(zhong)，制成碘(dian)的(de)乙(yi)醚溶(rong)(rong)(rong)液(ye)。乙(yi)醚是一種有機物(wu)(wu)，不能(neng)導電。把(ba)銀塊投入溶(rong)(rong)(rong)液(ye)中(zhong)(zhong)，溶(rong)(rong)(rong)解了(le)的(de)碘(dian)能(neng)夠與(yu)銀反(fan)應(ying)，在(zai)銀的(de)表面生(sheng)(sheng)產碘(dian)化(hua)(hua)銀膜(mo)。石油(you)中(zhong)(zhong)往往含(han)(han)(han)有硫(liu)(liu)、硫(liu)(liu)化(hua)(hua)氫(qing)及某(mou)些含(han)(han)(han)硫(liu)(liu)的(de)有機物(wu)(wu)，石油(you)中(zhong)(zhong)還含(han)(han)(han)有少(shao)量水，這少(shao)量的(de)水一般不能(neng)與(yu)硫(liu)(liu)的(de)化(hua)(hua)合物(wu)(wu)形(xing)成導電溶(rong)(rong)(rong)液(ye)，但它卻能(neng)加速硫(liu)(liu)的(de)化(hua)(hua)合物(wu)(wu)與(yu)金屬(shu)發生(sheng)(sheng)化(hua)(hua)學(xue)反(fan)應(ying)，成為反(fan)應(ying)的(de)催化(hua)(hua)劑。例如，硫(liu)(liu)化(hua)(hua)氫(qing)可(ke)與(yu)鐵、鉛、銅(tong)、汞(gong)、銀等反(fan)應(ying)，生(sheng)(sheng)成這些金屬(shu)的(de)硫(liu)(liu)化(hua)(hua)物(wu)(wu)，單質硫(liu)(liu)也可(ke)與(yu)銅(tong)、汞(gong)、銀等金屬(shu)反(fan)應(ying)，所以儲存石油(you)的(de)容(rong)器(qi)(qi)上部或(huo)蓋(gai)子往往被硫(liu)(liu)化(hua)(hua)氫(qing)腐蝕(shi)(shi)。在(zai)煉油(you)廠，常采用耐硫(liu)(liu)化(hua)(hua)氫(qing)腐蝕(shi)(shi)的(de)鋁(lv)箔(bo)來保(bao)護這些容(rong)器(qi)(qi)。

化(hua)學腐蝕比較簡單，而且只在(zai)某(mou)些特(te)定(ding)條件(jian)下才會發生(sheng)。在(zai)生(sheng)產和日常生(sheng)活(huo)中普遍存在(zai)的(de)(de)、破壞(huai)最(zui)嚴重(zhong)的(de)(de)是(shi)電(dian)化(hua)學腐蝕，它是(shi)金屬常患的(de)(de)“風濕病”。

電(dian)(dian)(dian)(dian)(dian)化腐蝕是指金(jin)屬(shu)(shu)與電(dian)(dian)(dian)(dian)(dian)解(jie)質(zhi)溶(rong)液(ye)作用(yong)所發生的(de)(de)(de)腐蝕。它的(de)(de)(de)特點(dian)是在(zai)腐蝕過(guo)程中(zhong)有電(dian)(dian)(dian)(dian)(dian)流(liu)產生，這是金(jin)屬(shu)(shu)表面發生腐蝕電(dian)(dian)(dian)(dian)(dian)池作用(yong)的(de)(de)(de)結果(guo)。通常在(zai)電(dian)(dian)(dian)(dian)(dian)化腐蝕中(zhong)規定，電(dian)(dian)(dian)(dian)(dian)極電(dian)(dian)(dian)(dian)(dian)位(wei)較低的(de)(de)(de)金(jin)屬(shu)(shu)為(wei)(wei)陽極，電(dian)(dian)(dian)(dian)(dian)極電(dian)(dian)(dian)(dian)(dian)位(wei)較高的(de)(de)(de)金(jin)屬(shu)(shu)為(wei)(wei)陰極。當兩種電(dian)(dian)(dian)(dian)(dian)極電(dian)(dian)(dian)(dian)(dian)位(wei)不(bu)(bu)同(tong)的(de)(de)(de)金(jin)屬(shu)(shu)相接(jie)觸，或同(tong)種金(jin)屬(shu)(shu)的(de)(de)(de)不(bu)(bu)同(tong)的(de)(de)(de)部位(wei)具有不(bu)(bu)同(tong)電(dian)(dian)(dian)(dian)(dian)極電(dian)(dian)(dian)(dian)(dian)位(wei)時，它們(men)侵入電(dian)(dian)(dian)(dian)(dian)解(jie)質(zhi)溶(rong)液(ye)（潮濕(shi)氣(qi)體、海水、酸、堿、鹽的(de)(de)(de)水溶(rong)液(ye)或土壤等）后會變(bian)形成腐蝕電(dian)(dian)(dian)(dian)(dian)池。結果(guo)，作為(wei)(wei)陽極的(de)(de)(de)（電(dian)(dian)(dian)(dian)(dian)極電(dian)(dian)(dian)(dian)(dian)位(wei)低的(de)(de)(de)）金(jin)屬(shu)(shu)，由于(yu)不(bu)(bu)斷失去電(dian)(dian)(dian)(dian)(dian)子并(bing)將自(zi)己的(de)(de)(de)離(li)子投入溶(rong)液(ye)而被腐蝕，而作為(wei)(wei)陰極的(de)(de)(de)（電(dian)(dian)(dian)(dian)(dian)極電(dian)(dian)(dian)(dian)(dian)位(wei)高的(de)(de)(de)）金(jin)屬(shu)(shu)由于(yu)僅起著傳遞電(dian)(dian)(dian)(dian)(dian)子的(de)(de)(de)作用(yong)，本身(shen)沒有發生腐蝕及其他(ta)變(bian)化。