Nile Blue and Indigo Carmine organic dyes as corrosion inhibitor of mild steel in hydrochloric acid

The inhibiting behavior of Nile Blue and Indigo Carmine organic dyes on mild steel corrosion was evaluated in 1 M HCl solution, separately, by weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy techniques. Results show that the inhibition efficiency (%IE) increases with the increasing concentration of Indigo Carmine up to 9.65 × 10⁻⁰⁵ M (%IE ~ 98) and Nile Blue up to 1.08 × 10⁻⁰⁴ (%IE ~ 75–80). Good agreement was found between the results obtained from the different techniques used. Polarization curves indicate that the inhibition of the both inhibitors is of a mixed anodic–cathodic nature, and Langmuir isotherm is found to be an accurate isotherm describing the adsorption behavior. The inhibition mechanism of the inhibitors involves chemisorption interaction between the inhibitor and the mild steel. The inhibition efficiency for both inhibitors decreased by the rising temperature in the range of 25–55 °C, and these results verified the chemisorption behavior of both the inhibitors.