Protection of zinc, galvanized steel and “galvanic zinc–steel” contact couples by chamber corrosion inhibitors. Authors’ review

The review summarizes the authors’ studies on the chamber protection of zinc, galvanized steel, and “galvanic zinc–steel” contact couples. It was found that effective chamber protection of zinc is provided by α-branched carboxylic acids such as ethylhexanoic acid (EHA) and neodecanoic acid (NDA). Zinc and galvanized steel have a similar but not identical corrosion-electrochemical behavior. Nevertheless, the optimum temperature and duration of chamber treatment of these materials with EHA and NDA are the same. Nano-sized polymolecular adsorption films are formed on the metal surface under optimal conditions of chamber treatment of zinc and galvanized steel in EHA and NDA vapors. They passivate the metals and stabilize their passive state in chloride-containing media. These films inhibit the thermal oxidation of zinc and are capable of structuring on exposure of electrodes in the air during one day after chamber treatment. This structuring is accompanied by a growth in zinc protection efficiency. It has been found that the basic salt C4H9–CH(C2H5)–COO–Zn–OH is formed on the metal in the course of chamber treatment. Dehydrogenation of the salt takes place upon exposure in the air with formation of the compound C4H9–CH(C2H5)–COO–Zn–O–Zn–OOС–CH(C2H5)–C4H9, which provides zinc protection. The protection of zinc and galvanized steel from corrosion by EHA and NDA occurs by a blocking mechanism. Protective films formed during chamber treatment of zinc with EHA and NDA have the self-healing ability in the case of mechanical damage to their integrity. Effective simultaneous protection of zinc and carbon steel is provided by mixtures of EHA with urotropine or octadecylamine. Treatment of samples with EHA and NDA vapors can be used for temporary protection of zinc and galvanized steel products. It is expedient to use mixtures of EHA with octadecylamine or urotropine for temporary protection of “galvanic zinc–steel” contact couples.