Adsorption and corrosion inhibition behaviour of acid red on AISI 4130 alloy steel in HCl solution

Abstract

The inhibition behaviour of 2-(N,N-Dimethyl-4-aminophenyl)azobenzenecarboxylic acid (acid red) on the corrosion resistance of AISI 4130 steel in 1 M HCl solution has been studied by potentiodynamic polarization (Tafel), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). Polarization studies indicate that the inhibition efficiency increases with the increase in inhibitor concentration and inhibitor retard both the cathodic and anodic reactions so classified as mixed type inhibitors. EIS data has been analyzed to equivalent circuit model and show that as the inhibitor concentration increased the charge transfer resistance of steel increased whilst double layer capacitance decreased. The effect of temperature on the corrosion behavior of steel in HCl with the addition of the inhibitor was studied in the temperature range from 25-65°C. The experimentally obtained adsorption isotherms follow the Langmuir equation. Activation parameters and thermodynamic adsorption parameters of the corrosion process such as E_a, ΔH, ΔS, K_ads and ΔG°_ads are calculated at different temperatures and using the adsorption isotherm. The morphology of steel surface after its exposure to HCl solution in the absence and presence of inhibitor has been examined by SEM images.