For many years, the goal of transitioning from conventional to renewable fuels (bioethanol and biodiesel) has been encouraged by government entities. However, due to the hygroscopicity of ethanol, ethanol/biodiesel blends can accelerate corrosion in metallurgy. Therefore, inhibitors can be added to mitigate corrosion. This research studied the effect of adding ethanol to diesel/biodiesel blends and measured the rate of corrosion on various metals (aluminum, copper, and 304 stainless steel) by the electrochemical impedance spectroscopy (EIS) method. The results indicated the corrosion rate increased with increasing the percentage of ethanol in the blends, and the corrosion inhibition efficiency of tert-butylhydroquinone (TBHQ) decreased upon the addition of ethanol. TBHQ was most effective as a corrosion inhibitor in the B15E5 blend. The inhibition efficiency of TBHQ decrease with the increase of the temperature. The adsorption process and the electrochemical parameters were calculated and discussed.

Bitter orange, Citrus Aurantium (CA), extract and one of its chemical constituents, Linalool, have been evaluated as a corrosion inhibitor for mild steel in 0.5 mol L-1 hydrochloric acid (HCl) solution using potentiodynamic polarization, electrochemical impedance, Fourier transform infrared spectroscopy (FTIR), and atomic force spectroscopy (AFM) techniques. Functional groups of CA and Linalool were identified by FTIR spectroscopy. The Potentiodynamic polarization and electrochemical impedance studies showed that CA and Linalool act as mixed type inhibitors. The activation parameters showed that the corrosion inhibition takes place by spontaneous physical adsorption on the mild steel surface. Thermodynamic-kinetic model and Flory-Huggins isotherms were used to investigate the adsorption characteristics of CA and Linalool. The surface morphologies of mild steel specimens were studied using AFM, in which the surface roughness of the metal specimens on a micro scale was characterized.