The corrosion of mild steel and cast iron in cleaning solutions with different inhibitors (aliphatic and aromatic acids) was studied by measurements of corrosion potentials, i-U curves and the geometric shape of the pits. The industrial conditions were simulated by tap water (TW) with 50 mM borate (pH 9.4, 70°C) and a wet or dry atmosphere of 298 K. The most effective inhibition was obtained in solutions with the passivating Toluylalanine (TALA). This inhibitor yielded the strongest anodic shift of the pitting potential and an inhibition of pit growth even after the anodic initiation in diluted solutions. Ex situ investigations by a light microscope yielded the number, depth and lateral radii of the pits. The enrichment of salt and the formation of concentrated electrolytes during the dry/wet cycles was simulated in bulk electrolytes with increasing chloride concentrations. TALA gives a protection even at higher chloride concentrations. A Scanning-Kelvin-Probe was applied to map the varying activity of the protected and unprotected surface. This proves the anodic shift of the potential and the stabilization of the oxide film. © 1994.
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