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The protective efficacy of volatile inhibitors (VCI) of IFKhAN-A series (A-8, 112, 114, 118) against atmospheric corrosion of carbon steel St3 was studied at room temperature in air in the presence of corrosion stimulants (CS) at specified concentrations: CO2 (0.2–0.6) vol.%, H2S (10–30) mg/m 3 and NH3 (20–60) mg/m 3 . The relative humidity was 100%. Corrosion tests were carried out in sealed containers of 7 liters in volume (desiccators) in two versions. In one version, only one CS was introduced into the air atmosphere. In the other, two or all three used CS were simultaneously injected into the gas phase. To create equilibrium concentrations of the CS in the air atmosphere, a special technique has been developed. The duration of the corrosion tests was 240–528 hours. Potentiodynamic polarization measurements were performed at a potential sweep rate of 0.66 mV/s immediately after immersing the electrodes in the solution and after 24 to 96 hours of their stay in the corrosive medium (in situ). In the presence of CO2 in air atmosphere, the protective efficiency of all the VCIs studied is close to 100%. In the presence of NH3 (20 mg/m 3 ), it is within 74% (IFKhAN-8) to 21% (IFKhAN-118). In the presence of H2S, the protective effect of the VCIs increases again, amounting to 93–97%. In uninhibited systems containing simultaneously two stimulants of corrosion, intense pitting is observed. When CO2 and NH3 are introduced simultaneously, the protective effect of the investigated VCIs is in the range of 76–87%, with CO2+H2S it is 81% (A-112 and 118) to 100% (A114), and with H2S+NH3, it is 67–85%. The most effective is IFKhAN-114, which not only reduces the corrosion rate, but also eliminates pitting (CO2+NH3). Introduction of IFKhAN-114 allows one to achieve the protective effect of 95% in the presence of all three CS simultaneously. The corrosion rate of steel in the uninhibited background solution is limited by the cathodic reaction. In the presence of (NH4)2S as an NH3 and H2S reaction Int. J. Corros. Scale Inhib., 2018, 7, no. 2, 175–184 176 product, the IFKhAN-114 inhibitor effectively inhibits the anodic process. As a result, the corrosion potential of steel is increased by 0.070 V. The protective effect of IFKhAN-114 obtained from the data of potentiodynamic measurements in this medium immediately after immersing the electrode in the solution, is about 50%. This is lower than the value calculated from the results of gravimetric measurements, due to the different duration of steel aging in the corrosive environment. Received: February 2, 2018. Published: May 4, 2018 doi: 10.17675/2305-6894-2018-7-2-5

Protection of carbon steel against atmospheric corrosion by volatile inhibitors of IFKhAN series at high concentrations of CO2, H2S and NH3