| Popis: |
Optical and scanning electron microscopy of ion‐implanted aluminum after polarization above the pitting potential in have shown that corrosion pits are associated with the formation and rupture of blisters caused by gas evolution. The sequence of events involves: (i) the formation or existence of a primary crack or pore in the oxide film that allows solution contact with the metal, (ii) metal dissolution and hydrogen production at the oxide/metal interface, (iii) formation of a hydrogen pocket (bubble) that stresses the oxide film and causes the nucleation and growth of secondary cracks at the primary crack/pore, (iv) and the eventual rupture of the blister caused by the increasing hydrogen pressure. Griffith‐type calculations show that the internal hydrogen pressure required to rupture a typical blister is of the order of 103 atm, whereas thermodynamic data indicate that the internal hydrogen pressure generated within localized corrosion cells on aluminum is about 104 atm. |
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