The inhibition effect of castor bark powder obtained from Ricinus communis on AISI 1020 carbon steel in acidic media (HCl 0.5 mol.L -1 ) has been studied by electrochemical impedance spectroscopy (EIS), polarization curves, scanning vibrating electrode technique (SVET) and weight loss measurements. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were employed as characterization techniques. The EIS and gravimetric results showed that the inhibitory efficiency increases with inhibitor concentration achieving 83%. Polarization curves indicated that the castor bark powder acts as mixed inhibitor. The adsorption of the powder components on the metal surface follows the Langmuir isotherm. The FTIR analyses indicate the presence of C, N and O heteroatoms, incorporated in functional groups mainly related to the presence of carboxylic acids as ricinoleic acid, which could be responsible for the inhibitory properties of the powder. SEM analyses showed that the corrosion process was retarded in the presence of inhibitor in the electrolyte, which was confirmed by SVET measurements. Therefore, the results indicate that castor bark powder has potential to be a corrosion inhibitor for carbon steel in acidic media.

The malt bagasse is a solid residue, highly produced in the brewing industry. The presence of high levels of antioxidants in its composition makes this residue an attractive possibility as a corrosion inhibitor, besides being a sustainable and low cost alternative to the inorganic procedures currently used to prevent corrosion. In this sense, this work evaluated the efficiency of the malt bagasse powder as a corrosion inhibitor on the surface of AISI 1020 carbon steel, in different concentrations, in acidic medium 0.5 mol.L -1 HCl. The resistance to corrosion was tested by electrochemical techniques, such as electrochemical impedance spectroscopy (EIS) and anodic and cathodic polarization curves. The efficiency of the corrosion inhibitor was evaluated by weight loss tests. Fourier transform infrared spectroscopy (FTIR) and optical microscope surface image analysis were respectively used as chemical and morphological characterization techniques, respectively. From the EIS results, it can be said that the powder has its efficiency increased once the concentration is higher. On the other hand, the polarization curves shows the malt bagasse powder as an inhibitor presents both anodic and cathodic behavior. The weight loss results confirmed the electrochemical results, showing 92.5% efficiency for the 1.77 g.L-1 concentration. The adsorption isotherm on the steel surface follows Languimir's Isotherm. The FTIR analysis indicates the presence of heteroatoms such as C, N, O, incorporated in functional groups that could be responsible for the inhibitory properties found in the powder. The images obtained from the optical microscope, showed that the corrosion process, in the presence of the inhibitor in the electrolyte, is retarded. Therefore, the results indicate that the malt bagasse powder has the potential to be a corrosion inhibitor for steel in acidic medium, adding value in the beer production chain.

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This work investigates the use of (Allium sativum L.) garlic peel extract, and (Theobroma L) cacao peel, as well as their synergy as a corrosion inhibitor for carbon steel in 0.5 mol.L-1 hydrochloric acid solution. The comparative study was performed in 1.11 g.L-1 of extract. The investigation was carried out using Fourier transform infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS), gravimetric techniques and scanning electron microscopy (SEM) as chemical, electrochemical and morphological characterization techniques, respectively.  Gravimetric tests results showed a reduction in the corrosion rate of the extracts, with 90.7% efficiency for garlic extract and 89% for cacao extract, however, the mixture of the compounds presented an inhibition superior to 98%, showing the great synergism between the studied species. While the EIS results showed a higher impedance module value for cacao extract compared to garlic extract. Chemical analysis for extracts of garlic and cacao obtained by FTIR showed the presence of compounds based on sulfur and nitrogen, which are responsible for corrosion inhibiting effect. The SEM images obtained showed the formation of a film which reduces the evaluation of the corrosive process. Then, it is possible to conclude, that the carbon steel surface immersed in 0.5 mol.L-1 HCl solution with garlic peel extracts or cacao peel extracts or both, presents a corrosion inhibiting effect.