Continuous Studies on Using Camel’s Urine as Nontoxic Corrosion Inhibitor–Corrosion Inhibition of Al–Cu Alloy in Alkaline Solutions

Abstract

The corrosion inhibition of Al–Cu alloy in 0.5 M NaOH using various concentrations of camel urine (CU) was investigated using hydrogen evolution, weight loss, electrochemical impedance spectroscopy and potentiodynamic polarization measurements. Analysis of impedance spectra revealed that CU inhibits the corrosion of the studied alloy effectively through the formation of a protective film on its surface with a resistance increasing with increasing CU concentration. Polarization studies indicated that CU was a mixed-type inhibitor except for CU concentrations > 3 mL% where it behaves predominantly as an anodic inhibitor. Hydrogen evolution plots were analyzed using shrinking core models for solid–liquid heterogeneous systems. The resultant data revealed that after certain induction period, hydrogen evolution occurs by fast reaction followed by slow reaction and the latter is controlled by diffusion. The values of IE% obtained from hydrogen evolution and weight loss measurements were temperature dependent. Generally, the inhibitor performance decreased at relatively high temperature (60 $$^{\circ }$$ C) except for low CU concentrations (< 3 mL%) the inhibition efficiency improved with temperature increase. The apparent activation energy for Al–Cu alloy corrosion in the inhibited solutions was calculated and compared with that in the uninhibited solution. El-Awady and Temkin adsorption isotherms fit well the adsorption data obtained from weight loss at 30 $$^{\circ }$$ C and 60 $$^{\circ }$$ C. Based on El-Awady and Temkin isotherms, multilayer film formation with repulsive forces between the adsorbed molecules was suggested. Various thermodynamic parameters for the adsorption process were calculated and discussed. Thermodynamic data indicated comprehensive adsorption (chemisorptions and physical adsorption). Good assessment to correlate the inhibition mechanism with the CU composition was obtained.