RESUMO
The concentration effect of Tradescantia spathacea (T. spathacea) as corrosion inhibitor of API 5L X52 steel in 0.5 M of H2SO4 was studied here through electrochemical and gravimetric techniques. To achieve it, samples of the material were prepared to be submitted to each of the tests. Results from electrochemical impedance spectroscopy (EIS) showed that there was an optimum concentration of the inhibitor in which is reached the maximum inhibition efficiency, displaying the best inhibition characteristics for this system with a maximum inhibition of 89% by using 400 ppm. However, the efficiency decreased until 40% when the temperature was increased to 60°C. Potentiodynamic polarization curves (PDP) revealed that some of the present compounds of T. spathacea may affect anodic and cathodic process, so it can be classified as a mix-type corrosion inhibitor for API 5L X52 in sulfuric acid. Also, this compound followed an adsorption mechanism; this can be described through a Frumkin isotherm with an adsorption standard free energy difference (ΔG°) of -56.59 kJmol-1. Metal surface was studied through scanning electron microscope, results revealed that by adding inhibitor, the metal surface is protected; also, they evidenced low damages compared with the surface with no inhibitor. Finally, Tradescantia spathacea inhibited the corrosion process with 82% efficiency.
RESUMO
In this paper, the influence of a nickel binder metal and molybdenum carbide as an additional alloying element on the microstructure and corrosion behavior of WC-based cemented carbides, processed by conventional powder metallurgy, was studied, and a comparison with conventional cemented carbide (WC-Co) was carried out. The sintered alloys were characterized, before and after corrosive tests, by analyses using optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. The corrosion resistance of the cemented carbides was investigated by open circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy in a 3.5 wt.% NaCl solution. The WC-NiMo cemented carbides showed microstructures similar to those of WC-Co; however, pores and binder islands were observed in the microstructures. The corrosion tests showed promising results, the WC-NiMo cemented carbide showed superior corrosion resistance and higher passivation capacity than the WC-Co cemented carbide. The WC-NiMo alloy showed a higher EOC ≈-0.18 V vs. Ag|AgCl|KCl3mol/L than the WC-Co (EOC≈-0.45 V vs. Ag|AgCl|KCl3mol/L). The potentiodynamic polarization curves showed lower current density values throughout the potential range for the WC-NiMo alloy, and it was observed that Ecorr was less negative (≈-0.416 V vs. Ag|AgCl|KCl3mol/L) than for WC-Co (≈-0.543 V vs. V vs. Ag|AgCl|KCl3mol/L). The EIS analysis confirmed low rate corrosion of WC-NiMo associated with the formation of a passive thin layer. This alloy showed a higher Rct (1970.70 Ω).
RESUMO
El presente trabajo pretende hacer un aporte al conocimiento del comportamiento electroquímico de recipientes de hojalata en medio del ion citrato, y al papel que juega la concentración de dicho ion en la estabilidad de los recipientes. Todo ello, a través del estudio electroquímico individual de los materiales con los cuales son fabricados los recipientes de hojalata, acero y estaño. El estudio se llevó acabo mediante medidas de polarización potenciodinámica e impedancia electroquímica sobre electrodos fabricados con ambos materiales e inmersos en soluciones de diferentes concentraciones de citrato a un valor de pH de 3,0. Se evidencia que a este valor de pH, el ion citrato ejerce un notable efecto de despolarización anódica sobre el estaño, por la formación de complejos solubles y estables. Esto hace que el estaño se torne anódico respecto al acero pudiendo otorgar una protección anticorrosiva al sustrato de acero de los recipientes de hojalata.
The present work tries to do a contribution to the knowledge of the electrochemical behavior of tinplate containers in citrate ion medium and the role that citrate ion concentration plays on the stability of the containers; all that, through the individual electrochemical study of the materials of which the tinplate is made, steel and tin. The study was done by potentiodynamic polarization and electrochemical impedance on electrodes made with both materials, immersed in solutions of different citrate concentrations at pH 3,0. It was evidenced that the citrate ion has a remarkable effect of anodic depolarization on tin with the formation of soluble and stable complexes. This causes that tin becomes anodic with respect to the steel being able to grant an anticorrosive protection to the steel substrate of the tinplate containers.
O presente trabalho tem como objetivo contribuir com o conhecimento do comportamento eletroquímico da folha de flandes em meios contendo íons citrato, bem como o papel que a concentração de íon citrato desempenha na estabilidade dos recipientes. Os estudos eletroquímicos foram conduzidos a partir dos materiais individuais que constituem o ferro estanhado, ou seja, o aço e o estanho. Os experimentos foram realizados utilizando- se técnicas de polarização potenciodinâmica e de impedância eletroquímica em eletrodos formados, separadamente, por aço e estanho que permaneceram imersos em soluções de citrato, a pH 3,0 com diferentes concentrações. Foi evidenciado que o íon citrato apresenta um efeito notável de depolarização anódica no estanho pela formação de complexos estáveis e solúveis. Consequentemente, o estanho se torna anódico em relação ao aço e oferece uma proteção anticorrosiva aos substratos de aço que constituem os recipientes de ferro estanhado.