交流電蝕時孔蝕行為之研究

Pitting Behaviors of Aluminum foils during AC Electrolytic etching

李偉任(Wei-Jen Li)

指導教授 ： 林招松

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2004年)

https://doi.org/10.6342/NTU.2004.00767

摘要

本研究於鹽酸溶液中探討電源波形、氯離子濃度、pH值，以及硫酸根對低壓陽極鋁箔交流電蝕之孔蝕行為的影響。利用動態循環伏安法(GVP)量測試片表面反應電壓對應電流和週期數的關係，並以掃描式電子顯微鏡(SEM)觀察鋁箔表面形貌，以及穿透式電子顯微鏡(TEM)觀察橫截面蝕孔深度、連結情形，和腐蝕生成物組成結構及厚度。
結果顯示方波為電蝕較有效率之波形，電蝕後穿蝕深度最深、表面蝕孔較大、溶蝕量較多、表面腐蝕生成物較厚等特點。由電化學量測可得知其單一電量和累積電量比三角波和正弦波多。鹽酸電解液中添加適量硫酸根導致蝕孔穿蝕深度變小，使蝕孔細緻均勻，減少表層未具蝕孔鋁掉落的機率，且在動態循環伏安曲線上發現電流同相峰增高和蝕孔再鈍化行為。在0.8M鹽酸電蝕液中添加1.6M氯離子造成破孔電位下降、電流同相峰下降、初期蝕孔發孔數量以及溶蝕量有顯著增加，氯離子增加有利於孔蝕初期蝕孔誘發。而將電蝕液pH調整較低時，導致負半週期過電位隨之減少，不利腐蝕生成物沈積，氯離子因而容易穿透較薄之腐蝕膜，致使發孔數量明顯增加，表面蝕孔細緻且連結嚴重。針對添加硫酸根、氯離子和pH值利用動態循環伏安法量測、無膠橫截面TEM觀察，並對腐蝕生成物影響及蝕孔形貌提出合理機制。

關鍵字

動態循環伏安法 ； 腐蝕生成物 ； 孔蝕 ； 破孔電位 ； 交流電蝕

並列摘要

Aluminum foils used as the anode of low-voltage capacitors were etched in hydrochloric acid using an ac current to investigate how the current waveforms and the concentration of Cl-, H+ as well as SO42- affect the pitting behavior of the foils. The voltage/current relationship at a specific cycle was measured via a galvanostatic voltammetry polarization (GVP) method. The surface morphology of etched foils of which the etch films had been removed was observed using SEM. Finally, cross-sectional TEM was employed to characterize the coalescence and propagation of the pits, as well as the microstructure and thickness of the etch film.
When etched using the square current waveform, the foils suffered the greatest amount in weight loss and consisted of the largest and deepest pits that were covered with relatively thick etch films. Meanwhile, GVP shows that during each cycle the total charges expended in the dissolution of the foil were larger for the square waveform than that of the triangular and sinusoidal waveforms. Adding SO42- in hydrochloric acid resulted in finer pits with less penetration depth, thereby effectively preventing the loss of aluminum due to undermining of the pits. Furthermore, following initial dissolution, the foil was passivated in the presence of SO42-, as illustrated by the in-phase I/V shown in the GVP curve. Chloride ions in 0.8 M hydrochloric acid caused a decrease in the breakdown voltage and in-phase peak voltage, while resulted in an increase in initial nucleation of the pits and the weight loss. Finally, less etch films precipitated in the solution with lower pH. Since Cl- could easily penetrate through the thinner etch films, more finer pits nucleated and tended to merge together with each other.
Based on microstructural characterizations and GVP measurements, possible mechanisms regarding the nucleation, growth, coalescence and propagation of the pits are discussed in details and include the effect of H+, Cl- and SO42- in hydrochloric acid.

並列關鍵字

Galvanostatic Volt ； AC Electrolytic etching,pitting

參考文獻

5. C. S. Lin and C. C. Chiou, “Etch Pit Nucleation and Growth Film Formation of the AC Electrograined Aluminum Plates,” 第三屆海峽兩岸材料腐蝕與防護研討會論文集, pp.57-62.

1. C. K. Dyer and R. S. Alwitt, “Surface Changes during A.C. Etching of Aluminum,” J. Elctrochem. Soc., Vol.123, 1981, pp.300-305.

2. B. J. Wiersma and K. R. Hebert, “Observations of the Early Stages of the Pitting Corrosion of Aluminum,” J. Electrochem. Soc., Vol.138, 1991 pp.48-54.

3. H. Uchi, T. Kanno and R. S. Alwitt, “Structural Features of Crystalline Anodic Alumina Films,” J. Electrochem. Soc., Vol.148, No.1, 2001, pp.B17-B23.

7. M. Baumgartner and H. Kaeche, “Microtunnelling during localized attack of Passive Aluminum: The case of Salt Films vs Oxide Films,” Corrosion Science Vol.29, No.2/3, 1989, pp.363-378.