The inhibition effect of the cocoa bean shell powder (CBSP) on SAE 1008 carbon steel was studied in acidic medium (HCl 0.5 mol L -1 ) by electrochemical techniques and gravimetric measurements. Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) were used to the chemical and morphological characterization. The gravimetric and EIS results showed that the corrosion rate decreases with increasing inhibitor concentration, reaching the maximum value of 97.92% in 1.77 g L -1 inhibitor (highest concentration studied). Even at the lowest concentration (0.44 g L -1 ) good corrosion inhibition efficiency (96.03%) was observed. The polarization curves indicated that the CBSP acts as a mixed type inhibitor. The inhibitory molecules adsorption followed the Langmuir isotherm model. The inhibitor economic evaluation showed that the use of CBSP is 48-616 times cheaper than traditional inhibitors. The results showed that CBSP is an efficient corrosion inhibitor for carbon steel and its production is financially attractive.

Carbon steel is used in various applications because of its excellent weldability, good mechanical resistance and low cost. However, its application becomes restricted due to its low corrosion resistance in neutral and acidic media, and it is necessary to use processes to retard the corrosive mechanism, such as the use of inhibitors. Many of the effective synthetic inhibitors used are associated with high cost and some have a high toxicity. In recent years, studies of corrosion inhibitors obtained from natural products have been increasing because they are environmentally sustainable and presents low-cost. Therefore, in the present study, different concentrations of the cocoa shell powder (Theobroma cacao) and hydroalcoholic extract were evaluated as a corrosion inhibitors of SAE 1008 carbon steel in 0.5 mol.L -1 sodium chloride solution. The inhibitory action of the cocoa residue was studied through gravimetric technique and electrochemical impedance spectroscopy (EIS). For the chemical characterization of the inhibitor, the Fourier Transform Infrared Spectroscopy (FTIR) was used. The EIS results showed that the corrosion inhibition efficiency of the steel decreased with the inhibitor concentration, reaching maximum values of 55.97% and 72.93%, for cocoa shell powder and hydroalcoholic extract, respectively. The gravimetric data confirmed the electrochemical results and through the study of the adsorption mechanism it was verified that the adsorbed inhibitor molecules follow the Flory-Huggins isotherm model, for both forms of the inhibitor. For all the concentrations evaluated, the cocoa shell powder did not represent an efficient corrosion inhibitor. In contrast, for the hydroalcoholic extract, at the concentration of 0.44 g.L -1 , a good performance was verified as a corrosion inhibitor of SAE 1008 carbon steel in 0.5 mol.L -1 sodium chloride solution.

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.