Assessment of the protective effectiveness of a volatile inhibitor in atmospheric corrosion of steel under conditions of increased concentrations of carbon dioxide, ammonia and hydrogen sulfide by electrochemical methods

The effect of the combined presence of atmospheric corrosion stimulants NH3 and CO2 was modeled by introducing (NH4)(2)CO3 salt into the solution. And the presence of NH3 and H2S was modeled by introducing the corresponding amounts of NH4OH and H2S into the solution. The presence of these corrosion stimulants in the air is characteristic for livestock buildings. The influence of the concentration of (NH4)(2)CO3 and (NH4)(2)S salts (10-500 mg/L) and the IFKHAN-114 volatile inhibitor (100 mg/L) during the corrosion of St3 steel in a 0.1 M NaCl solution was studied using methods of potentiodynamic polarization and spectroscopy of electrochemical impedance. Potentiodynamic measurements at a potential sweep rate of 0.66 mV/s were carried out in a three-electrode electrochemical cell made of Pyrex glass with a platinum auxiliary electrode and silver-silver chloride reference electrode using an IPC-Pro MF potentiostat. It was shown that in the absence of IFKHAN-114, the products of the hydrolysis of both salts as a result of their almost complete conversion to ammonium hydroxide and the corresponding weak acids cause intensive inhibition of corrosion of St3 carbon steel in 0.1 M NaCl solution. The protective effect reaches 90-96%. Introduction of IFKHAN-114 (100 mg/L) at low concentrations of (NH4)(2)CO3 (10 mg/L) has a stimulating effect on St3 steel, but starting with 20 mg/L of the salt this effect is replaced by an inhibitory one. Its value increases with increasing salt concentration, reaching 67% with a formal content of 100 mg/L ammonium carbonate in the solution. In the presence of ammonium sulfide, the protective effect is maximum at a low salt content (10 mg/L) and significantly decreases with increasing salt concentration, more precisely the products of its complete hydrolysis. The impedance measurements confirm the results obtained by the method of potentiodynamic polarization.