145 research outputs found
Crossover of interface growth dynamics during corrosion and passivation
We study a model of corrosion and passivation of a metalic surface in contact
with a solution using scaling arguments and simulation. The passive layer is
porous so that the metal surface is in contact with the solution. The volume
excess of the products may suppress the access of the solution to the metal
surface, but it is then restored by a diffusion mechanism. A metalic site in
contact with the solution or with the porous layer can be passivated with rate
p and volume excess diffuses with rate D. At small times, the corrosion front
linearly grows in time, but the growth velocity shows a t^{-1/2} decrease after
a crossover time of order t_c ~ D/p^2, where the average front height is of
order h_c ~ D/p. A universal scaling relation between h/h_c and t/t_c is
proposed and confirmed by simulation for 0.00005 <= p <= 0.5 in square
lattices. The roughness of the corrosion front shows a crossover from
Kardar-Parisi-Zhang scaling to Laplacian growth (diffusion-limited erosion -
DLE) at t_c. The amplitudes of roughness scaling are obtained by the same kind
of arguments as previously applied to other competitive growth models. The
simulation results confirm their validity. Since the proposed model captures
the essential ingredients of different corrosion processes, we also expect
these universal features to appear in real systems.Comment: 17 pages, including 7 figures; submitted articl
Corrosion behavior of friction stir welded lap joints of AA6061-T6 aluminum alloy
In this work, the corrosion behaviors of friction-stir lap welding of 6061-T6 Al-alloy are studied. The friction-stir lap welding was performed under different welding conditions (rotation speed and welding speed). The corrosion behavior of the parent alloy, the weld nugget zone (WNZ), and the heat affected zone (HAZ) of each welded sample working as an electrode, were investigated by the Tafel polarization test in 3.5 wt. (%) NaCl at ambient temperature. The morphology of the corroded surface of each region was analyzed by scanning electron microscopy together with energy dispersive spectroscopy (SEM-EDS). The results showed that the corrosion resistance of the parent alloy was better than the WNZ and the HAZ in both welding conditions. Localized pit dissolution and intergranular corrosion were the dominant corrosion types observed in the parent alloy, WNZ, and HAZ. The parent alloy, WNZ, and HAZ exhibited similar corrosion potentials (Ecorr) after T6 heat treatment. This treatment had a better effect on the corrosion resistance of the welded regions than the parent alloy
Galvanic replacement reaction: A simple and powerful route to hollow and porous metal nanostructures
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