Experimental and theoretical investigations for some spiropyrazoles derivatives as corrosion inhibitors for copper in 2 M HNO3 solutions

Abstract

Rates of corrosion for copper were monitored in aerated stagnant 2 M HNO3 solutions at different temperatures (25-55 °C) using Tafel extrapolation method, electrochemical impedance spectroscopy technique, non-destructive electrochemical frequency modulation (EFM) technique and weight-loss method, accompanied by EDX examinations, molecular docking, molecular dynamics, and quantum chemical calculations. Some spiropyrazoles derivatives were introduced as corrosion-safe inhibitors. Compound (1) has the best inhibition activity (89.9% at 11 × 10−6M). Tafel plots indicated that these compounds acted mainly as mixed-type inhibitors. The inhibition process was ascribed to the formation of an adsorbed film on the copper surface that protects the metal against corrosive agents. EDX examinations of the electrode surface confirmed the existence of such adsorbed film. The inhibition efficiency increased by increasing the concentration of spiropyrazoles compounds, while it decreased by increasing the temperature, this expresses on the physical adsorption. Activation energy has been calculated in the existence and nonexistence of a number of concentrations from spiropyrazoles derivatives by measuring the corrosion rate obtained from the weight loss method at different temperatures. It was found that the activation energy in the presence of spiropyrazoles derivatives is higher than that in 2 M HNO3 solution alone. The adsorptive behavior of spiropyrazoles compounds followed Freundlich -type isotherm.