以電化學原子力顯微鏡進行420不銹鋼於氯化鈉水溶液之即時腐蝕行為研究

The in-situ Corrosion Study of the AISI 420 SS in the Sodium Chloride Aqueous Solution by Electrochemical AFM

原子力顯微鏡（AFM）可應用於各種材料表面，並在真空、大氣或水溶液的環境中使用，是分析與觀察材料表面奈米結構的利器，結合恆電位／電流儀與原子力顯微鏡的電化學原子力顯微鏡（ECAFM）可即時提供材料表面於電化學反應過程之奈米尺度的結構變化，是發展奈米科技的重要儀器。
本研究以電化學原子力顯微鏡直接觀察420不銹鋼（以下簡稱420SS）於0.001 M氯化鈉水溶液中的常溫即時腐蝕行為，並搭配傳統之腐蝕電位儀實驗結果，進行定電位電化學腐蝕研究。由即時擷取之不銹鋼表面形貌影像發現，試片表面之平均粗糙度隨著浸泡腐蝕時間增加而變大；試片表面之鈍化膜亦被侵蝕破裂，試片表面之各種大小形態蝕孔亦能完整觀察，蝕孔之深度自數十奈米至數百奈米不等。420SS於長時間浸泡腐蝕之後，表面生成直徑約200至300奈米之顆粒狀腐蝕生成物。本研究並結合掃描式電子顯微鏡分析420SS表面之腐蝕生成物的形態，以做為電化學原子力顯微鏡分析觀察之佐證。

Atomic force microscope (AFM) is a powerful tool to examine and analysis the surface morphologies and structures on nano scale. It can be applied in the vacuum, air and liquid environments and suitable for almost all kinds of materials. The electrochemical atomic force microscope combines the potentiostat with AFM together to provide the surface structure information during electrochemical reaction.
In situ nano scale pitting corrosion images of 420SS in 0.001 M NaCl aqueous solution has been investigated by the electrochemical atomic force microscope in this study. Granular corrosion products, surface corrosion pits, cracked and spalled passivation films are observed. The size of the corrosion pits is around several tens to several hundred nm in depth. After long testing time, lots of granular corrosion products ranging 200 to 300 nm in diameter are observed on the surface. It is concluded that the ECAFM is a useful tool to study the in situ corrosion phenomena on stainless steels.