鍍鋅鋼板之腐蝕與電化學行為

Corrosion and electrochemical behavior of coating zinc sheet steel

呂振嘉(Chen-chia Lu)

指導教授 ： 李雄

國立中央大學/工學院/機械工程學系/碩士(2008年)

摘要

本研究探討熱浸鍍鋅鋼板(SGCC)、電鍍鋅鋼板(SECC)、55%鋁鋅鋼板(SGLC)在不同pH值之3% NaCl溶液中的電化學行為，利用浸泡腐蝕和開路電位量測、Tafel極化和循環極化來評估鍍鋅鋼板的腐蝕與電化學現象。
比較開路電位與重量損失，SGLC在大氣中表面會生成氧化鋁層且具有保護作用，使得在重量損失量較少且開路電位量測偏向貴重，但在pH=11溶液下，此氧化層容易被破壞而導致腐蝕訊速提升。SGCC與SECC在酸性下表面生成之氧化層為不穩定狀態，容易分解，使得重量損失量隨著pH值降低而增加、開路電位隨著pH值降低而區傾向活性，但在鹼性下時表面會會逐漸生成具有保護的氫氧化鋅層而保護鍍層。
從Tafel極化結果中，在不同pH值之3% NaCl溶液中，除了在pH=11以外，其抗腐蝕能力由大而小依序為: SECC＞SGLC＞SGCC；然而在pH=11時，SGLC腐蝕速率忽然提高，所以在此環境下其抗腐蝕能力由大而小依序為:SECC＞SGCC＞SGLC。
在循環極化曲線中，SGLC只有在pH=11下才有鈍態特徵的出現且以負磁滯曲線呈現，而SGCC皆有明顯的鈍態特徵但保護能能力不佳，使的鈍態區無法完整呈現並造成局部腐蝕，SECC有完整的鈍態膜，但容易受到不同的pH值的影響而造成的孔蝕產生且嚴重的破壞到基材上。

關鍵字

鍍鋅鋼板 ； 電化學行為 ； Tafel極化 ； 循環極化

並列摘要

Hot-dip zinc、electroplating zinc and 55%Al-Zn coating were investigated for comparison of their corrosion resistance, electrochemical behavior in 3% NaCl of varying with pH value solution. The assessment corrosion and electrochemical phenomenon of coating zinc sheet steel were employed with immersed corrosion, opening circuit potential, Tafel polarization, cyclic polarization.
Compared with the OCP and weight loss, SGLC surface is covered by aluminum oxide layer which protects the function. The result is that its weight lost less and OCP towards to the noble potential. But in pH=11, this oxide layer is easier destroyed to cause the corrosion rate rise. However, the surface of SGCC and SECC is formed the oxide layer with unstable in acidic environment, and it is easy to decompose, to cause weight loss increase with the pH decreases and the OCP decrease with the pH decreases. But in the alkalinity environment is covered by the oxide layer which transformed from the degrees of Zinc hydroxide to protect coating.
From Tafel polarization, 3% NaCl of varying with pH value solution except pH=11, its corrosion resistant ability decreases for SECC＞SGLC＞SGCC. In pH=11, SGLC corrosion rate are enhanced in the short time. Therefore, the corrosion resistance which is under this environment decreases in order to SECC＞SGCC＞SGLC.
In cyclic polarization, SGLC only has the passive state characteristic appearance also presents by the negative hysteresis curve in pH=11. SGCC has obviously passive state characteristic, but its protected ability is not good enough. The result of the passive state area is unable to do the completely display, and to create the localized corrosion. SECC has entirely passive membrane, but it is easy to different pH value accessibly. Above of all will cause pitting formation which will also make the serious destruction to the substrate on.

並列關鍵字

coating zinc sheet steel ； electrochemical behavior ； cyclic polarization ； Tafel polarization

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