Electrochemical investigation on effect of sodium thiosulfate (Na2S2O3) and ammonium chloride (NH4Cl) on carbon steel corrosion

Abstract

The effect of sodium thiosulfate (Na2S2O3) concentrations (0.01, 0.1 and 1M) on carbon steel corrosion behavior in 3.75M ammonium chloride (NH4Cl) solution was investigated. The potentiodynamic polarization results show that the icorr increases from 8.7×10−6Acm−2 to 7.2×10−4Acm−2 when thiosulfate (S2O32−) concentration increases from 0 to 1M. Electrochemical impedance spectroscopy measurements also mimic the same trend. However, it is also observed that the icorr value starts decreasing when S2O32− concentration equals or exceeds the NH4Cl concentration (Cl−:S2O32−≥1:1) in the electrolyte solution. The polarization behavior and field-emission scanning electron microscopy images reveal that the carbon steel undergoes general corrosion at lower concentrations (0.01M S2O32− and 0.1M S2O32−) and, both pitting and general corrosion at higher concentration (1M S2O32−). Based on the experimental results, the mechanistic reaction pathway, which involves two dissolution paths for carbon steel dissolution is suggested.