Dynamics of Protective Layers Formation during Steel Inhibition by Sulfanilamide in Hydrochloric Acid Solutions with Different pH

Using the method of polarization resistance, it has been proved that there are peculiarities in the formation of protective layers during steel inhibition by Sulfanilamide in aqueous solutions of hydrochloric acid with different pH, resulting from the predominance of protonated or deprotonated forms of molecules. At pH <= 2.4 (predominantly protonated form) dense protective films are formed, while at pH >= 2.4 (predominantly deprotonated form) loose layers are formed that do not inhibit diffusion processes. High (> 90 %) and stable efficiency of Sulfanilamide inhibition in acidic media can be provided only by the protective films formed of protonated molecules, which must be considered when using the inhibitor.