Morphological evolution of tunnel tips for aluminum foils during DC etching

Abstract

The morphologies of tunnel tips in different stages for aluminum foils during DC etching in 1.5 mol/L HCl solution at 90°C were observed by field emission scanning electron microscopy (FE-SEM). A novel model was proposed to describe the morphological evolution of tunnel tips throughout the growth processes. In the pit nucleation stage, the pits vary from the hemispherical to half-cubic shapes due to the activation of pit tips from the center to the edge. During the tunnel growth stage, the pits dissolve toward the depth direction and develop into the tunnels, and their tips remain flat. In the tip passivation stage, as the passivation of tunnel tips speeds up from the edge to the center, the tunnel tips change from flat shapes to three-dimensional protrusions. The mechanism may be attributed to the order of activation or passivation on the tunnel tips changed in different stages.

Keywords

aluminum / corrosion / pitting / polarization / etching / electrolytic capacitors

References

[1] Alwitt RS, Uchi H, Beck TR, Alkire RC. Electrochemical tunnel etching of aluminum. J. Electrochem. Soc., 1984, 131(1): 13.

[2] Hebert K, Alkire R. Growth rates of aluminum etch tunnels. J. Electrochem. Soc., 1988, 135(10): 2447.

[3] Makino E, Yajima T, Shibata T, Ikeda M, Tanno Y, Suganuma E. In situ observations of growing pits during tunnel etching of aluminum. Mater. Trans. JIM, 1993, 34(9): 796

[4] Szklarska-Smialowska Z. Pitting corrosion of aluminum. Corros. Sci., 1999, 41(9): 1743.

[5] Osawa N, Fukuoka K. Pit nucleation behavior of aluminium foil for electrolytic capacitors during early stage of DC etching. Corros. Sci., 2000, 42(3): 585.

[6] McCafferty E. Sequence of steps in the pitting of aluminum by chloride ions. Corros. Sci., 2003, 45(7): 1421.

[7] Xiao RG, Yan KP, Yan JX, Wang JZ. Electrochemical etching model in aluminum foil for capacitor. Corros. Sci., 2008, 50(6): 1576.

[8] Ono S, Habazaki H. Effect of sulfuric acid on pit propagation behaviour of aluminium under AC etch process. Corros. Sci., 2009, 51(10): 2364.

[9] Ono S, Habazaki H. Pit growth behaviour of aluminium under galvanostatic control. Corros. Sci., 2011, 53(11): 3521.

[10] Sheng H, Dong CF, Xiao K, Li XG, Lu L. Anodic dissolution of a crack tip at AA2024-T351 in 3.5wt% NaCl solution. Int. J. Miner. Metall. Mater., 2012, 19(10): 939.

[11] Liang LB, He YD, Song HZ, Yang XF, Cai XY, Xiong CY, Li YR. Effect of hydration pretreatment on tunnel etching behaviour of aluminium foil. Corros. Sci., 2013, 70, 180.

[12] Beck TR. Salt film formation during corrosion of aluminum. Electrochim. Acta, 1984, 29(4): 485.

[13] Muthukrishnan K, Hebert KR. Kinetic model for aluminum dissolution in corrosion pits. J. Electrochem. Soc., 2004, 151(2): B45.

[14] Hebert K, Alkire R. Growth and passivation of aluminum etch tunnels. J. Electrochem. Soc., 1988, 135(9): 2146.

[15] Wiersma BJ, Hebert KR. Observations of the early stages of the pitting corrosion of aluminum. J. Electrochem. Soc., 1991, 138(1): 48.

[16] Ono S, Makino T, Alwitt RS. Crystallographic pit growth on aluminum (100). J. Electrochem. Soc., 2005, 152(2): B39.

[17] Tak Y, Sinha N, Hebert KR. Metal dissolution kinetics in aluminum etch tunnels. J. Electrochem. Soc., 2000, 147(11): 4103.

[18] Makino T. Growth of crystallographic pits and tunnels on (100) aluminum. J. Surf. Finish. Soc. Jpn., 2005, 56(11): 636.

[19] Xiao RG, Yan KP. Tunnel morphology of aluminum foil etched by a two-step DC etching method. Corros. Sci., 2008, 50(11): 3256.

[20] Jeong JH, Choi CH, Lee DN. A model for the ¿ crystallographic tunnel etching of aluminium. J. Mater. Sci., 1996, 31(21): 5811.

[21] Wiersma BJ, Tak Y, Hebert KR. Passivation of surfaces within aluminum etch tunnels. J. Electrochem. Soc., 1991, 138(2): 371.