Evaluation of the protective efficiency of a volatile corrosion inhibitor of atmospheric corrosion of metals in the presence of aggressive micro impurities of air by impedance spectroscopy method

The protective efficiency of the volatile IFHAN-114 corrosion inhibitor (VCI) was determined by impedance spectroscopy under atmospheric corrosion of St3 steel and copper in livestock buildings containing trace amounts of carbon dioxide, ammonia and hydrogen sulfide in the regulatory allowable concentrations. A 0.1 M NaCl solution was used as the background electrolyte. The effect of the combined presence of NH3 and CO2 corrosion stimulants of metals in the air was modeled by introducing (NH4)2CO3 in concentrations of 10 and 100 mg/L into the background solution. To simulate the combined presence of NH3 and H2S in air, equivalent amounts of Na2S and NH4Cl were introduced into the background electrolyte solution to obtain (NH4)2S (10 and 100 mg/L) at specified concentrations. This resulted in the hydrolysis of NH4 + and S2- ions to form NH4OH and H2S, which are stable in the surface phase film. According to impedance spectroscopy, (NH4)2CO3 at a concentration of 10 mg/L acts as an corrosion inhibitor of steel in a 0.1 M NaCl solution, and IFKHAN-114 (nonequivalent mixture of polyaniline with benzoic acid), introduced into the solution along with this amount of ammonium carbonate, plays the role of a corrosion stimulator. However, with an increase in the concentration of ammonium carbonate, its inhibitory effect is decreased, and for IFKHAN-114, introduced along with the salt, on the contrary, is appeared. A similar pattern is observed for the copper electrode. In the presence of (NH4)2S, almost the same effect of salt and VCI is observed for steel and copper, but with some variation. A comparison of the data obtained by gravimetric tests and impedance measurements showed that in the latter case only qualitative results can be obtained, although they undoubtedly confirm the presence of the inhibitory ability of IFKHAN-114 in a chloride neutral solution.

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