Ammonium phosphate as inhibitor to mitigate the corrosion of steel rebar in chloride contaminated concrete pore solution

In the present study, different amounts, i.e., 1–3 v/v% of 1 M ammonium phosphate monobasic, were used as an eco-friendly corrosion inhibitor to mitigate the corrosion of steel rebar exposed to simulated concrete pore (SCP) + 3.5 wt% NaCl solution at a prolonged duration. Potentiodynamic polarization results show that as the amount of inhibitor is increased, the corrosion resistance of steel rebar is increased. The steel rebar exposed to 3% inhibitor-containing SCP + 3.5 wt% NaCl solution exhibited nobler corrosion potential (E_corr), the lowest corrosion current density (i_corr), and 97.62% corrosion inhibition efficiency after 1 h of exposure. The steel rebars exposed to 3% inhibitor-containing SCP + 3.5 wt% NaCl solution revealed higher polarization resistance (R_p) and film resistance (R_o) with exposure periods compared to other samples owing to the formation of passive film. The scanning electron microscopy (SEM) of steel rebar exposed to 3% inhibitor-containing SCP + 3.5 wt% NaCl solution showed homogenous and uniform dendritic passive film which covers all over the surface, whereas, bare, i.e., SCP + 3.5 wt% NaCl solution exposed samples exhibited pitting and irregular morphology. Raman spectroscopy results confirm the formation of goethite (α-FeOOH), maghemite (γ-Fe₂O₃), and iron phosphate (FePO₄) as a passive film onto the steel rebar surface exposed to 3% inhibitor-containing SCP + 3.5 wt% NaCl solution. These phases are responsible for the corrosion mitigation of steel rebar which are very protective, adherent, and sparingly soluble.