Valeriana officinalis root extract as a green corrosion inhibitor for carbon steel in 1.0 M hydrochloric acid solution

In recent years, a large number of synthetic compounds have been reported as corrosion inhibitors. Although synthetic compounds exhibit good anti-corrosion properties, most of them are very toxic to the environment and human life. The toxic effects of synthetic compounds have led to the replacement of natural products as anti-corrosion materials [1-3]. In this study, the corrosion inhibition characteristics of Valeriana officinalis root extract (VFRE) were investigated on carbon steel immersed in 1 M HCl media. The corrosion inhibition performance of VFRE was evaluated by means of weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods. Weight loss experiments were done as a function of the VFRE concentration and immersion time in 1.0 M HCl solution. The highest inhibition efficiency of 94.7 % was obtained in the presence of 1.0 g L-1 VFRE after about 10 hours of immersion time which shows that this extract is a fairly good inhibitor. Polarization curves indicated that VFRE is a mixed (cathodic/ anodic) type inhibitor. The effect of temperature on the efficiency of VFRE was done by electrochemical polarization method in the range of 35-65°C. Adsorption of VFRE on the surface of carbon steel, in this range of temperature, follows the Langmuir adsorption isotherm. It is guessed that the presence of valrenic acid, valerenol, and valernyl acetate containing extract decreases the corrosion rate of carbon steel in acidic solution. Therefore, theoretical methods such as quantum mechanics (QM) and molecular dynamics simulations (MDS) were used for suggest how the absorption of these molecules on the surface. MDS method evidenced that all major constituents exist in VFRE can be adsorbed to steel surface and form a protective film on the surface of carbon steel.