Inhibition of Aluminium Alloy Corrosion by Thiourea and Lithium Ion in 3.5 % NaCl Solution Using Gravimetric, Adsorption and Theoretical Studies

The adsorption and inhibition performance of thiourea and lithium ion on aluminium corrosion in 3.5% NaCl were investigated using gravimetric measurement, scanning electron microscope (SEM) analysis and quantum chemical computational techniques respectively. Gravimetric analysis revealed that thiourea has a good inhibitory efficacy of 82% at 1 mM concentration of thiourea on the corrosion inhibition of aluminum under the conditions studied. Also, poor inhibitory effects were recorded with an increase in the concentration of inhibitor, and improvement in inhibition efficiency was observed with the addition of lithium ion. In addition, the effects of temperature (303–333K) on corrosion inhibition was investigated. The findings showed that the effectiveness of the inhibition rises with temperature. The adsorption of thiourea molecules onto an aluminium surface followed the Temkin adsorption isotherm, while the mixed inhibitor of thiourea and lithium ion followed the Langmuir adsorption isotherm model. SEM results confirmed that the inhibition mechanism is due to the formation of a protective thin film on the aluminium surfaces that prevents corrosion. Quantum chemical calculations based on the density functional theory (DFT) revealed that the presence of sulphur and nitrogen in the structure of thiourea molecules is responsible for the strong inhibitory performance due to possible adsorption with Al atoms on the metal surface. The computed experimental and theoretical parameters in this investigation are in good agreement.