ABSTRACT 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.

RESUMO A hidroxiapatita tem se destacado entre os materiais cerâmicos devido a sua versatilidade estrutural, pois permite a substituição do Ca2+ ou do PO43-da sua estrutura possibilitando diversas aplicações. A utilização da hidroxiapatita como suporte e, ou catalisador tem recebido destaque como tema de pesquisa. Com isso, o objetivo deste trabalho foi a síntese, modificação e caracterização da hidroxiapatita para aplicação como catalisador em reação de esterificação. A hidroxiapatita foi obtida pelo método de precipitação e modificada por troca iônica no estado sólido, utilizando Zn(NO3)2 como precursor. As cerâmicas resultantes foram caracterizadas por análise térmica, espectrometria na região do Infravermelho por transformada de Fourier, difração de Raios-X e teste de acidez de Bronsted. Os catalisadores preparados, o HAP e o Zn-HAP foram avaliados frente à reação de esterificação do ácido oléico com metanol com as seguintes condições reacionais: razão metanol : ácido oléico (20:1), 10% m/m de catalisador e 3 h de reação a 150 °C apresentando conversões de 16,9% e 37,0%, respectivamente. Estes resultados são interessantes, principalmente do ponto de vista econômico, por se tratar de materiais de baixo custo utilizados como suporte para catalisadores heterogêneos.

ABSTRACT Hydroxyapatite has stood out among the ceramic materials due to their structural versatility as it allows the replacement of Ca2 + or PO43-its structure enabling various applications. One area that is gaining prominence is the application of hydroxyapatite as support and or catalyst. Thus, the objective of this work was the synthesis, modification and characterization of hydroxyapatite for use as a catalyst in esterification reaction. The hydroxyapatite was obtained by the precipitation method and was modified by solid state ion-exchange method using Zn(NO3)2 as precursor. The resulting ceramics were characterized by thermal analysis, Fourier Transform Infrared Spectroscopy, X-ray diffraction and Bronsted acidity test. The catalysts HAP and Zn-HAP prepared were evaluated against the esterification reaction of oleic acid with methanol under the following reaction conditions: ratio methanol: oleic acid (20:1), 10% m/m of catalyst and 3h reaction at 150 °C showing conversions of 16.9% and 37.0%, respectively. These results are interesting, mainly from the economical point of view, since they are low cost materials used as support for heterogeneous catalysts.

Corrosion represents high losses to the economy, therefore, researches on the minimization of its damages in materials, mainly the metallic ones, are necessary. Among the various alternatives of protection against corrosion, there is the application of corrosion inhibitors that can minimize or even stop the corrosive process of metallic materials. However, at present, substances usually used as corrosion inhibitors present high toxicity, being considered harmful components to the environment and to human health. Therefore, there is an urgent need for studies on viable corrosion inhibitors, by considering not only economic but also environmental costs. The present work studied the use of cocoa bark extract (Theobrama cacao L), for possible replacement of benzotriazole (BTAH) in the corrosion inhibition of ASTM 1020 carbon steel (CS- ASTM 1020) in 18.23 g.L-1 hydrochloric acid media. Weight loss measurements, anodic and cathodic potentiodynamic polarization curves and electrochemical impedance experiments were carried out. The results showed that the addition of the extract to the electrolyte effectively hinder the corrosion process and indicated its adsorption on the electrode surface. In addition, the inhibiting efficiency of the cocoa bark extract was only slightly inferior to BTAH, showing that it can be an environmentally friendly option to toxic inhibitors.