一塊金(jin)(jin)屬(shu)(shu)，表面看來挺光(guang)滑(hua)，可(ke)是在(zai)顯(xian)微鏡下就會發現，它(ta)的(de)(de)(de)結構很不均勻，這就為(wei)“病從(cong)口入”大(da)開了(le)方便(bian)之門，因為(wei)金(jin)(jin)屬(shu)(shu)遍(bian)體都是“口”，準確(que)一點說(shuo)，不是病從(cong)口入，而是病從(cong)“皮”入了(le)。所(suo)以金(jin)(jin)屬(shu)(shu)的(de)(de)(de)常(chang)見病--腐蝕，一般都開始于“皮膚病”。首先(xian)是金(jin)(jin)屬(shu)(shu)“皮膚潰瘍”，然后逐漸侵(qin)入到內部。由于金(jin)(jin)屬(shu)(shu)接觸的(de)(de)(de)物質多(duo)種多(duo)樣，“得病”的(de)(de)(de)條(tiao)件也(ye)各不相同，所(suo)以金(jin)(jin)屬(shu)(shu)的(de)(de)(de)常(chang)見病還可(ke)以分為(wei)許(xu)多(duo)種。也(ye)就是說(shuo)，金(jin)(jin)屬(shu)(shu)腐蝕可(ke)以分為(wei)許(xu)多(duo)種類。

金(jin)屬腐蝕(shi)(shi)分(fen)類的(de)方法(fa)很多，常見的(de)一種就是(shi)(shi)根據腐蝕(shi)(shi)過程中是(shi)(shi)否有電(dian)流產(chan)生，分(fen)為化學(xue)腐蝕(shi)(shi)和電(dian)化學(xue)腐蝕(shi)(shi)兩(liang)類。化學(xue)腐蝕(shi)(shi)一般(ban)是(shi)(shi)在干燥和高溫的(de)環(huan)境下(xia)發生的(de)，它是(shi)(shi)金(jin)屬的(de)“干熱病”；電(dian)化學(xue)腐蝕(shi)(shi)是(shi)(shi)在潮(chao)濕的(de)環(huan)境下(xia)發生的(de)，它是(shi)(shi)金(jin)屬的(de)“風濕病”。

 化(hua)(hua)學腐蝕(shi)(shi)是金屬(shu)(shu)在不導電環境(jing)中的腐蝕(shi)(shi)，它是金屬(shu)(shu)與某種(zhong)(zhong)物質直(zhi)接接觸時(shi)發生的化(hua)(hua)學反(fan)應。在化(hua)(hua)學腐蝕(shi)(shi)中，和(he)金屬(shu)(shu)接觸發生反(fan)應的物質可(ke)以(yi)是氣體(ti)，也可(ke)以(yi)是液(ye)體(ti)，所以(yi)化(hua)(hua)學腐蝕(shi)(shi)又分為(wei)氣體(ti)腐蝕(shi)(shi)和(he)液(ye)體(ti)腐蝕(shi)(shi)兩(liang)種(zhong)(zhong)。

 在(zai)(zai)高(gao)溫下，或(huo)周圍沒有導電(dian)物質(zhi)的(de)(de)條件(jian)下，金(jin)(jin)屬(shu)與空(kong)氣(qi)或(huo)其(qi)他其(qi)他發生(sheng)(sheng)反應，表面生(sheng)(sheng)成(cheng)氧(yang)(yang)化物或(huo)其(qi)他化合物的(de)(de)現(xian)象(xiang)，稱為氣(qi)體腐蝕(shi)(shi)。自然界中，氣(qi)體腐蝕(shi)(shi)的(de)(de)現(xian)象(xiang)也是很多(duo)。例(li)如，鐵在(zai)(zai)空(kong)氣(qi)中或(huo)氧(yang)(yang)氣(qi)中加熱時，表面會(hui)生(sheng)(sheng)成(cheng)鐵的(de)(de)氧(yang)(yang)化物膜；鋁在(zai)(zai)空(kong)氣(qi)中會(hui)與氧(yang)(yang)氣(qi)反應，表面生(sheng)(sheng)成(cheng)一層(ceng)氧(yang)(yang)化鋁薄(bo)膜。像這樣，金(jin)(jin)屬(shu)與周圍的(de)(de)物質(zhi)接觸(chu)發生(sheng)(sheng)反應生(sheng)(sheng)成(cheng)了(le)(le)化合物，我(wo)們就說金(jin)(jin)屬(shu)被腐蝕(shi)(shi)了(le)(le)，生(sheng)(sheng)成(cheng)的(de)(de)化合物（膜）就是腐蝕(shi)(shi)的(de)(de)產物（常稱作銹(xiu)）。

金屬在(zai)不導(dao)電(dian)的(de)(de)(de)液(ye)(ye)體里的(de)(de)(de)腐(fu)(fu)蝕(shi)(shi)也是一種(zhong)化(hua)學腐(fu)(fu)蝕(shi)(shi)，叫做液(ye)(ye)體腐(fu)(fu)蝕(shi)(shi)。銀(yin)可(ke)與(yu)(yu)(yu)碘發(fa)生(sheng)液(ye)(ye)體腐(fu)(fu)蝕(shi)(shi)。例(li)如(ru)把碘溶(rong)解于乙醚(mi)(mi)中(zhong)，制成(cheng)碘的(de)(de)(de)乙醚(mi)(mi)溶(rong)液(ye)(ye)。乙醚(mi)(mi)是一種(zhong)有機物(wu)(wu)，不能(neng)(neng)導(dao)電(dian)。把銀(yin)塊(kuai)投入溶(rong)液(ye)(ye)中(zhong)，溶(rong)解了(le)的(de)(de)(de)碘能(neng)(neng)夠與(yu)(yu)(yu)銀(yin)反應(ying)(ying)，在(zai)銀(yin)的(de)(de)(de)表(biao)面生(sheng)產碘化(hua)銀(yin)膜。石(shi)油(you)中(zhong)往往含(han)有硫、硫化(hua)氫(qing)及(ji)某(mou)些含(han)硫的(de)(de)(de)有機物(wu)(wu)，石(shi)油(you)中(zhong)還含(han)有少量水，這(zhe)(zhe)少量的(de)(de)(de)水一般不能(neng)(neng)與(yu)(yu)(yu)硫的(de)(de)(de)化(hua)合(he)(he)物(wu)(wu)形(xing)成(cheng)導(dao)電(dian)溶(rong)液(ye)(ye)，但它卻(que)能(neng)(neng)加(jia)速(su)硫的(de)(de)(de)化(hua)合(he)(he)物(wu)(wu)與(yu)(yu)(yu)金屬發(fa)生(sheng)化(hua)學反應(ying)(ying)，成(cheng)為(wei)反應(ying)(ying)的(de)(de)(de)催化(hua)劑。例(li)如(ru)，硫化(hua)氫(qing)可(ke)與(yu)(yu)(yu)鐵、鉛、銅、汞、銀(yin)等反應(ying)(ying)，生(sheng)成(cheng)這(zhe)(zhe)些金屬的(de)(de)(de)硫化(hua)物(wu)(wu)，單質硫也可(ke)與(yu)(yu)(yu)銅、汞、銀(yin)等金屬反應(ying)(ying)，所(suo)以儲存(cun)石(shi)油(you)的(de)(de)(de)容器上(shang)部或蓋子(zi)往往被硫化(hua)氫(qing)腐(fu)(fu)蝕(shi)(shi)。在(zai)煉(lian)油(you)廠，常采用耐硫化(hua)氫(qing)腐(fu)(fu)蝕(shi)(shi)的(de)(de)(de)鋁箔來保護這(zhe)(zhe)些容器。

化(hua)學(xue)腐蝕比較簡(jian)單，而且(qie)只在(zai)某些特定(ding)條件下(xia)才會發生。在(zai)生產和日常(chang)生活(huo)中普(pu)遍(bian)存在(zai)的(de)、破壞最嚴重的(de)是(shi)電化(hua)學(xue)腐蝕，它是(shi)金屬常(chang)患的(de)“風濕病”。

電(dian)(dian)(dian)(dian)(dian)化(hua)腐(fu)蝕(shi)是指金(jin)(jin)屬(shu)(shu)與電(dian)(dian)(dian)(dian)(dian)解質溶(rong)液(ye)作(zuo)(zuo)用(yong)所發生(sheng)的(de)(de)(de)(de)(de)腐(fu)蝕(shi)。它(ta)的(de)(de)(de)(de)(de)特點是在(zai)腐(fu)蝕(shi)過(guo)程中有(you)(you)電(dian)(dian)(dian)(dian)(dian)流產生(sheng)，這是金(jin)(jin)屬(shu)(shu)表面發生(sheng)腐(fu)蝕(shi)電(dian)(dian)(dian)(dian)(dian)池作(zuo)(zuo)用(yong)的(de)(de)(de)(de)(de)結果。通常在(zai)電(dian)(dian)(dian)(dian)(dian)化(hua)腐(fu)蝕(shi)中規定，電(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)位較(jiao)低(di)的(de)(de)(de)(de)(de)金(jin)(jin)屬(shu)(shu)為(wei)陽(yang)極(ji)，電(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)位較(jiao)高的(de)(de)(de)(de)(de)金(jin)(jin)屬(shu)(shu)為(wei)陰極(ji)。當兩種(zhong)電(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)位不同(tong)的(de)(de)(de)(de)(de)金(jin)(jin)屬(shu)(shu)相接觸(chu)，或同(tong)種(zhong)金(jin)(jin)屬(shu)(shu)的(de)(de)(de)(de)(de)不同(tong)的(de)(de)(de)(de)(de)部位具有(you)(you)不同(tong)電(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)位時，它(ta)們侵入(ru)電(dian)(dian)(dian)(dian)(dian)解質溶(rong)液(ye)（潮濕氣(qi)體、海水、酸、堿、鹽的(de)(de)(de)(de)(de)水溶(rong)液(ye)或土壤等）后會變形(xing)成腐(fu)蝕(shi)電(dian)(dian)(dian)(dian)(dian)池。結果，作(zuo)(zuo)為(wei)陽(yang)極(ji)的(de)(de)(de)(de)(de)（電(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)位低(di)的(de)(de)(de)(de)(de)）金(jin)(jin)屬(shu)(shu)，由于不斷(duan)失去電(dian)(dian)(dian)(dian)(dian)子(zi)(zi)(zi)并將自己的(de)(de)(de)(de)(de)離(li)子(zi)(zi)(zi)投入(ru)溶(rong)液(ye)而被腐(fu)蝕(shi)，而作(zuo)(zuo)為(wei)陰極(ji)的(de)(de)(de)(de)(de)（電(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)位高的(de)(de)(de)(de)(de)）金(jin)(jin)屬(shu)(shu)由于僅起(qi)著傳(chuan)遞電(dian)(dian)(dian)(dian)(dian)子(zi)(zi)(zi)的(de)(de)(de)(de)(de)作(zuo)(zuo)用(yong)，本身沒(mei)有(you)(you)發生(sheng)腐(fu)蝕(shi)及(ji)其他變化(hua)。