Inhibition of corrosive processes in wet atmosphere

Toluylalanine (TALA) is an additive in industrial cleaning baths and an effective temporary inhibitor of the corrosion of steel in neutral and weak alkaline electrolytes as well as in wet atmosphere. In dependence on the relative humidity of the atmosphere and the presence of hygroscopic salts, thin water films condense. The interaction between the metallic surface and the condensed liquid depends strongly on the surface tension. In our case we obtained a hydrophilic effect after the adsorption of the inhibitor. It can be assumed, that the water of the cleaning bath drains off the metal much better than in the case of hydrophobic layers. These effects in the range of monolayers could be studied with the quartz microbalance due to the high sensitivity of this technique. Improving our model, we obtained a lower and homogenous deposition of salt after the dipping in solution with TALA, which causes also a reduced homogenous condensation of water. Thus, corrosive attacks become less probable. The reactions in the cleaning bath and in films of condensed water were investigated by electrochemical methods in bulk electrolytes. In the presence of inhibitor the corrosion potential was shifted into the anodic direction, simultaneously the thickness of the oxide layer was increased in the presence of TALA. The characteristic data of pitting corrosion were obtained from anodic potentiodynamic sweeps. These results show, that pitting is hindered by TALA. Besides the stabilization of the passive layer, the growth of pits is also inhibited and repassivation is accelerated. From the polarization of probes precorroded at wet atmosphere we yielded in solutions with TALA an re-inhibition, too. Additionally we observed in unprotected solutions the sensitivity of this method to active corrosion centers, which cause pitting at lower overvoltages