Comparative study of natural corrosion inhibitors for carbon steel in acidic medium

摘要

The deterioration of the metallic material originated from its interaction with the environment is called corrosion. In this way, corrosion is one of the main reasons for economic losses in the industrial sector. Carbon steel, due to its mechanical resistance, deformation ability and low cost is widely used in the industry in different applications. However, this metal has low corrosion resistance, which reduces its performance and service life. Corrosion protection methods include cathodic and anodic protection, metal coatings and corrosion inhibitors. As synthetic corrosion inhibitors commonly used are toxic and expensive, it is necessary to replace them with other corrosion inhibitors that are also efficient and environmentally friendly. The use of corrosion inhibitors extracted from plants due to the complexity and wide variety of chemical species in their composition arouses the scientific interest because as a promising alternative to protect against corrosion. Corrosion natural inhibitors are renewable, non-toxic, readily available, and economically viable and do not contain heavy metals. The objective of this work is to evaluate the extract obtained from avocado seed and palm kernel cake as natural corrosion inhibitors for ASTM 1020 carbon steel in acidic medium (0.5 mol.L~(-1) HCl). The alcoholic extracts were obtained by the Soxhlet method from the vegetable waste in the powder form The characterization of corrosion behavior was performed by weight loss measurements according to ASTM Glstandard and polarization curves. Fourier transform infrared spectroscopy (FTIR) was employed for prior chemical characterization of the compounds present in the extracts. Other techniques were performed to characterize extracts as natural corrosion inhibitors such as CG-MS, electrochemical impedance and SEM. The results of corrosion current densities obtained from the polarization curves showed inhibition efficiency of 90% and 81% for the alcoholic extract of avocado seed and palm kernel cake, respectively, in the concentration of 2.2 g.L~(-1). In addition, the polarization curves indicated that both extracts act as corrosion natural inhibitors of mixed type. The weight loss measurements also showed the reduction of corrosion rate. The chemical characterization of alcoholic extracts by FTIR suggests the presence of functional groups such as N-H, O-H, C = O, as well as C = C vibrations and aromatic rings, characteristic of phenolic compounds as flavonoids and other compounds with antioxidant effect, which can be responsible for the inhibitory properties. The results suggest that the molecules present in the studied plant extracts adsorb on the metallic surface, reducing the contact area between the metal and the corrosive medium, being these residues promising for corrosion inhibitors with greater inhibition efficiency for avocado seed.