The Effect of Chemiadsorbed Layers of Nitrilotris–Methylenephosphonate Complexes of Lead(II) with Bridging and Chelate Coordination on the Electrochemical Behavior of a Steel 20 Surface. Thermochemical Induction of Secondary Inhibition

Resumo

The effect of the chemiadsorbed layers of two lead(II) complexes of nitrilotris–methylenephosphonic acid, differing from one another in coordination of the Pb(II) atom, on the corrosion-electrochemical behavior of a Steel 20 surface in neutral aqueous medium with natural aeration, after deposition of the adsorption layers of the complexes and their heat treatment in air, was investigated. The adsorption layer of the complex with a bridging structure weakly retards the anodic dissolution of steel, and the heat treatment has almost no effect on the protective effectiveness. The adsorption layer of a complex with a chelate structure at medium temperatures also has a weak effect on the kinetics of anodic process; however, the change of the structure of the surface layer after heat treatment at 300°C results in a sharp decrease in the anode current and to refining of the steady-state corrosion potential. The conclusion was drawn that heat treatment induces chelate decomplexation and results in secondary inhibition of the surface of steel by products of the thermochemical transformation.