Effectiveness of one-to-one phosphate to chloride molar ratio at different chloride and hydroxide concentrations for corrosion inhibition of carbon steel

Abstract

In this work, the impact of pH on the corrosion inhibition of carbon steel by phosphate ions in solutions<br>with different contaminations of chloride ions (1, 10, and 100 mmol L1) with 1:1 phosphate to chloride<br>molar ratio was investigated using electrochemical methods including potentiodynamic polarization and<br>electrochemical impedance spectroscopy (EIS). Moreover, the electrochemical results were complemented<br>using surface analysis methods, including scanning electron microscopy (SEM), energy dispersive<br>spectroscopy (EDS), Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. The<br>obtained results showed that at the passivation pH (pHp), the corrosion state changes from active to passive.The value of pHp decreases with an increase in the concentration of phosphate ions and the protection against both uniform and pitting corrosion in the long term was improved. The phosphate inhibition on the carbon steel surface processed through the formation of a duplex layer, including iron (hydro)oxides (inner part) and iron phosphate complexes (outer part).