In this study, the influence of deaeration on the electrochemical behavior of aluminum was studied by polarization techniques. The advantages of deaeration for the evaluation of localized corrosion on aluminum are discussed. The influence of the corrosive environment with low oxygen contents on the electrochemical response of aluminum was evaluated by anodic and cathodic potentiodynamic polarization curves. The polarization tests were carried out in chloride solutions followed by optical and scanning electron microscopy characterization. It was observed that deaeration of the solution significantly influences the electrochemical behavior of aluminum, as predicted by corrosion kinetics theories. For the cathodic curves, a decrease in the limiting current density for the oxygen reduction reaction (ORR) was observed for low oxygen solutions, while the “apparent” initiation of the hydrogen evolution reaction (HER) was shifted to higher potentials. In the anodic curves, a common passive behavior was not observed in aerated conditions, however, at the corrosion potential, localized pitting was observed indicating that the material was already above the breakdown potential (Ebr). In the low oxygen content solution, however, a passive region with a breakdown potential, was observed on the anodic curves. study techniques discussed curves characterization theories ORR (ORR apparent “apparent HER (HER potentials conditions however Ebr. Ebr . (Ebr) (Ebr

Resumen La corrosión atmosférica es uno de los fenómenos naturales de mayor impacto en la integridad de las infraestructuras metálicas en todo el mundo, y en especial en ambientes tropicales. Sin embargo, la gran mayoría de los estudios de corrosión atmosférica realizados en ambientes naturales no superan los 5 años de exposición, y son más escasos aún los estudios con resultados de l0 o más años. En este estudio se evaluó la cinética de corrosión del acero al carbono y acero galvanizado expuestos en la zona céntrica de Medellín, catalogada como un ambiente de agresividad moderada, con base en resultados obtenidos tras l, 2, 5, 8 y il años de exposición. Para ambos materiales se obtuvo una ecuación cinética de corrosión mediante gráficas Log-Log de la pérdida de masa, de gran utilidad para hacer predicciones a largo plazo del deterioro de estructuras expuestas a la atmósfera. La corrosión del galvanizado fue aproximadamente entre l0 a l7 veces menor que la del acero al carbono.

Abstract Atmospheric corrosion is one of the natural phenomena with the greatest impact on the integrity of metallic infrastructures worldwide and especially in tropical environments. However, most atmospheric corrosion studies carried out in natural environments do not exceed 5 years of exposure, and studies with results of 10 or more years are even fewer. This study evaluates the corrosion kinetics of carbon and galvanized steels exposed in the downtown area of Medellín, classified as a moderate aggressiveness environment, from results obtained at 1, 2, 5, 8 and 11 years. For both materials, a corrosion kinetic equation was obtained from Log-Log plots of mass loss, useful for making long-term predictions of the deterioration of structures exposed to the atmosphere. The corrosion of the galvanized was approximately between 10 to 17 times lower than that of carbon steel.

Fly ash (FA) was used successfully as a carrier for the corrosion inhibitor molybdate and applied as an extender pigment in an epoxy coating. To enhance interaction, molybdate was attached to FA through intercalation in layered double hydroxide (LDH), facilitated by surface modification of FA. Molybdate was incorporated into LDH either via direct synthesis or ion exchange. Directly synthesized LDH significantly increased molybdate storage in FA. The FA-inhibitor combination was tested in three ways: molybdate release kinetics, corrosion of an ultra-low carbono (ULC) steel in chloride solution, protection of ULC steel conferred by particles embedded in an epoxy coating. Short-term molybdate release was favored by ion exchange, long-term release by deglomeration of LDH. ULC steel corrosion inhibition in 0.1 M NaCl reached 89%. Incorporating the material into epoxy coatings mitigated steel corrosion, validated by electrochemical impedance spectroscopy. This study underscores the efficacy of FA-LDH-molybdate systems in corrosion protection. (FA coating interaction LDH, , (LDH) exchange FAinhibitor ways kinetics ultralow ultra low (ULC solution Shortterm Short term longterm long 01 0 1 0. 89 89% spectroscopy FALDHmolybdate (LDH 8

Abstract Mild steel (MS) corrosion inhibition by Terminalia mantaly (TM), in 1.0 M HCl, was studied using weight loss and linear polarization methods, at different reaction conditions. Gas chromatography-mass spectrometry (GC-MS) was used to determine the possible extract components. Fourier transformed infrared spectroscopy (FTIR) and optical microscopy were used to investigate the interaction of the plant extract phytochemicals with the MS surface. The obtained results revealed that the inhibition efficiency percentage (IE%) increased with a decrease in the TM concentration, and decreased with a rise in temperature (T). The IE% also decreased as the hydrochloric acid (HCl) concentration increased. Inhibition occurred through the TM phyto-molecules adsorption onto the MS surface. The corrosion inhibition kinetics followed a zero order reaction, and it was uni-molecular. The linear polarization showed that TM is a mixed-type inhibitor. Gibb’s free energies values confirmed a spontaneous process, while TM adsorption onto the MS surface was found to obey physisorption, aligning with the Langmuir’s and El-Awady’s adsorption isotherm models.

RESUMEN El procesamiento de crudos con alto contenido de ácidos nafténicos causa problemas de corrosión en las unidades de detilación. El Número Total Ácido (TAN) es comunmente usado para evaluar la corrosividad de crudos, y por lo tanto es un parametro usado para la toma de decisiones relacionadas con el control de la corrosión de la refinerías. Sin embargo, el TAN solo representa el número de grupos carboxílicos presentes en el crudo y no considera las características estructurales de los ácidos nafténicos ni su reactividad en las reacciones de corrosión. En este trabajo se desarrolló el fraccionamiento de una mezcla comercial de ácidos nafténicos a partir de la solubilidad de sus respectivas sales. Se determinaron parámetros estructurales característicos de los ácidos nafténicos de cada fracción usando Espectroscopia de Infrarrojo, Cromatografía De Permeación en Gel, Resonancia Magnética Nuclear, Espectroscopia de Masas y Análisis Elemental. Se realizó el estudio cinético de la reacción de corrosión de un acero AISI 1005 expuesto a cada fracción de ácidos nafténicos en el rango de temperatura entre 270 y 350°C. Finalmente, se propuso un modelo de reacciones paralelas para la predicción de la concentración de hierro disuelto debido a la reacción de corrosión, a partir de la concentración molar de cada una de las fracciones que conforman la mezcla de ácidos nafténicos.

ABSTRACT Processing crudes with high naphthenic acid content causes corrosion problems on the crude oil distillation units. The total acid number (TAN) is commonly used to evaluate the corrosivity of crude oils; thus for decision-making related to corrosion mitigation and control in refineries. However, the TAN only represents the number of carboxylic groups present in the crude oil and does not consider the structural characteristics of the naphthenic acids, nor their reactivity, which are highly relevant to corrosion. On the other hand, the study of naphthenic acids as fractions with specific structural characteristics should enable the identification of differences in the corrosivity of crude oil with the same naphthenic acid concentration. In this research work, the fractioning of a commercial mixture of naphthenic acids was performed using the ionic strength of their respective salts. The structural characterization of the obtained fractions was conducted using Fourier-transform infrared and mass spectroscopy, gel permeation chromatography, and nuclear magnetic resonance. Furthermore, the corrosion rate of AISI SAE 1005 steel exposed to each fraction of naphthenic acids in the temperature range between 270 and 350 °C was determined. Based on these results, a kinetic model of parallel reactions for predicting the concentration of dissolved iron in crude oil containing a mixture of naphthenic acids is proposed and validated.

Resumen Integrar conocimientos es la tarea fundamental de la educación química y es en este contexto en el cual la investigación en inhibición de corrosión de acero nos brinda la oportunidad de llevarlo a la práctica. Esto permite integrar conocimientos de cinética electroquímica con química orgánica y química analítica instrumental vía el uso de un potenciostato de fuente abierta de bajo costo y su utilización en el estudio de las propiedades anticorrosivas del 1-fenil-H-tetrazol-5-tiol. Esta experiencia le permitirá al estudiante determinar la velocidad de corrosión de acero al carbono SAE 1020 en agua de mar simulada aireada, esto es una solución de NaCl al 3,0 % en peso saturada de oxígeno O2 en presencia y ausencia de 1-fenil-H-tetrazol-5-tiol en dos concentraciones en una celda electroquímica estándar de 3 electrodos en un rango entre -0,2 a -0,7 V vs. ENH.

Abstract Integrating knowledge is the fundamental task of chemistry education and it is in this context that research in steel corrosion inhibition gives us the opportunity to put it into practice. This allows the integration of knowledge of electrochemical kinetics with organic chemistry and instrumental analytical chemistry via the use of a low-cost open source potentiostat and its use in the study of the anticorrosive properties of 1-phenyl-H-tetrazole-5-thiol. This experience will allow the student to determine the corrosion rate of SAE 1020 carbon steel in aerated simulated seawater, this is a NaCl solution at 3.0% by weight saturated with oxygen O2 in the presence and absence of 1-phenyl-H- Tetrazole-5-thiol in two concentrations in a standard 3-electrode electrochemical cell in a range of -0.2 to -0.7 V vs. ENH.

The electro-oxidation of 4-amino-3-methyl-1,2,4-triazole-5-thione (MTSNH) on a bronze substrate in an alkaline methanol solution produces a homogeneous polymer film. The formation kinetics of the film was investigated using cyclic voltammetry, chronoamperommetry and electrochemical impedance spectroscopy. Cyclic voltammograms indicated that the polymer film (pMTSNH) was formed anodically between -350 and 350 mV/SCE. During the second cycle, the oxidation peak of the monomer disappeared, indicating the formation of the insulating film. We have also shown that the monomer oxidation reaction is essentially irreversible and controlled by a diffusion process. The inhibition efficiency of this polymer was determined by potentiodynamic polarization and electrochemical impedance spectroscopy in a 3.5% NaCl solution.

This work ultimately pays careful consideration to a method that respects the environment, and that can be developed across the accumulation of research to reduce the corrosion of metals in sea water. Extracts of Ziziphus lotus (wild jujube) were tested as a corrosion inhibitor of copper in sea water, using polarization methods and weight loss measurements. We also present by SEM the morphology of copper surface analyzed after immersion in inhibited and uninhibited electrolytes. The inhibition efficiency of Ziziphus lotus extracts was calculated and compared. We note good agreement between these methods. The obtained results revealed that the tested inhibitor significantly reduced the kinetics of the corrosion process of copper. Its efficiency increases with the concentration, and attained 93% at 5 g/L. The effect of temperature on the corrosion behavior of copper in natural sea water was also studied in the range of 293 K and 323 K, to determine thermodynamic data of activation.

Cefixime was investigated as a corrosion inhibitor for mild steel in an hydrochloric acid solution. The results revealed that the order of reaction is 0.427, with activation energy found to be 41.7 kJ/mol. Cefixime was effective in increasing the inhibition efficiency for all inhibition concentrations. The corrosion rate profile was found to be second- order kinetics with respect to corrosion activity.

A corrosão a alta temperatura dos encanamentos utilizados em equipamentos geradores de vapor (caldeiras) tem sido reconhecida como um grave problema que traz o adelgaçamento destas e, por conseguinte, a falha dos equipamentos. Na última década tem se incrementado as pesquisas que envolvem recobrimentos protetores que ajudam de alguma maneira a prolongar a vida útil destes equipamentos. Esta pesquisa determinou o comportamento dos recobrimentos NiCrAlY e NiCrFeNbMoTiAl depositados por projeção térmica assistida por plasma (APS) sobre a liga SA213 - T22 (2¼Cr - 1Mo), em um ambiente corrosivo de 80%V2O5 - 20%K2SO4 a 800°C. Os valores da cinética de corrosão foram determinados mediante resistência à polarização linear (RPL) e espectroscopia de impedância eletroquímica (EIE). Os resultados obtidos mostram uma menor cinética de corrosão no recobrimento NiCrFeNbMoTiAl que a apresentada pelo recobrimento NiCrAlY, corroborado por Microscopia Eletrônica de Varredura (MEV).

La corrosión a alta temperatura de las tuberías utilizadas en equipos generadores de vapor (calderas) ha sido reconocida como un grave problema que trae consigo el adelgazamiento de éstas y, por consiguiente, la falla de los equipos. En la última década se han incrementado las investigaciones que involucran recubrimientos protectores que ayudan de alguna manera a prolongar la vida útil de estos equipos. Esta investigación determinó el comportamiento de los recubrimientos NiCrAlY y NiCrFeNbMoTiAl depositados por proyección térmica asistida por plasma (APS) sobre la aleación SA213 - T22 (2¼Cr - 1Mo), en un ambiente corrosivo de 80%V2O5 - 20%K2SO4 a 800°C. Los valores de la cinética de corrosión fueron determinados mediante resistencia a la polarización lineal (RPL) y espectroscopia de impedancia electroquímica (EIE). Los resultados obtenidos muestran una menor cinética de corrosión en el recubrimiento NiCrFeNbMoTiAl que la presentada por el recubrimiento NiCrAlY, corroborado por Microscopia Electrónica de Barrido (MEB).

The corrosion at high temperature in pipes used in steam generating equipment (boilers), has been recognized as a serious problem, that results in the pipes thinning and therefore the equipments failure. In the last decade there has been a rise in investigations involving protective coatings to help, in some way to extend the useful life of these equipments. This investigation determined the NiCrFeNbMoTiAl and NiCrAlY coatings behavior, deposited by plasma-assisted thermal projection spraying (APS) on the alloy SA213 T22 (2¼Cr -1Mo), in acorrosive environment of 80 % V2O5- 20 % K2SO4 to 800 °C. The kinetics corrosion values were determined by linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS). The results obtained show a lower kinetic corrosion on the NiCrFeNbMoTiAl coating than the NiCrAlY coating, confirmed by the SEM, Scanning Electron Microscopy.

The corrosion inhibition of mild steel in hydrochloric acid by polyvinyl alcohol-gpoly( acrylamide-vinyl sulfonate) has been studied by weight loss and electrochemical methods (AC impedance and DC polarisation) techniques in the temperature range of 303 - 343 K. The inhibitor was found to provide an excellent efficiency of more than 90 %. Various adsorption isotherms have been employed for fitting the obtained results to confirm the mode of adsorption of the grafted terpolymer on mild steel. Thermodynamic parameters of adsorption such as equilibrium constant, Gibbs free energy, adsorption heat and adsorption entropy were evaluated and discussed. Various parameters that determine the kinetics of mild steel dissolution such as activation energy, enthalpy and entropy were also calculated. Results obtained from various techniques were comparable and suggest that the terpolymer follows chemical adsorption mode for inhibition.

En el presente trabajo, se evaluó la influencia del aumento de la temperatura en la velocidad de corrosión de la aleación Pb-Ca-Sn, componente primario de la rejilla negativa de una batería de arranque de automóvil, mediante técnicas electroquímicas: RPL, curvas potenciodinámicas, Tafel y EIS. Mediante microscopia óptica, SEM-EDS y DRX, se caracterizaron los compuestos formados sobre las rejillas durante los ensayos. La capa pasiva formada sobre las rejillas empleadas como cátodo y ánodo en baterías de plomo-ácido, permite el anclaje en la interfase rejilla-PAM (Material Activo Positivo) o NAM (Material Activo Negativo). Un mal proceso de formación de esta capa ocasiona el desprendimiento del PAM/NAM, conduciendo a fallas prematuras. La temperatura influye directamente sobre la cinética de degradación y la termodinámica de las reacciones redox que tienen lugar en el sistema rejilla-PAM/ NAM. Un incremento en la temperatura produce variaciones en la composición química, favoreciendo la formación de mezclas de óxidos y sulfatos en la interfase rejilla-PAM/NAM, cuyo volumen y estructura porosa la hace susceptible a fallas por esfuerzos triaxiales sobre la interfase, produciendo grietas y el desprendimiento del PAM o NAM y disminuyendo el tiempo de vida útil de la batería. Se encontró que las aleaciones Pb-Ca-Sn en solución 0,5M de H2SO4 forman un sistema multicapa comprobándose con base en los resultados obtenidos de EIS y SEM, con los cuales se detectó una capa compacta de PbO2 y una capa porosa de PbSO4. Al incrementar la temperatura se encontró una capa más porosa de PbSO4, lo cual implica una mayor cinética de corrosión de la aleación Pb-Ca-Sn.

In this paper, the influence of increasing temperature on the corrosion rate of Pb-Ca-Sn alloy, the primary component of the negative grid of a starter battery car, was evaluated by electrochemical techniques: RPL, potentiodynamic curves, Tafel and EIS. By optical microscopy, SEM -EDS and XRD, the compounds formed on the grids were characterized during testing. The passive layer formed on the grids used as cathode and anode in lead-acid batteries allows the anchor in grid-PAM interface (Positive Active Material) or NAM (Negative Active Material). A bad process of to form this layer produces the detachment of PAM/NAM, leading to premature failure. The temperature directly affects the kinetics and thermodynamics degradation of the redox reactions taking place in the system grid-PAM/NAM. An increase in temperature causes variations in the chemical composition, favoring the formation of oxides and sulphates mixtures in grid-PAM/NAM interface, its volume and porous structure make it susceptible to failure by tri-axial stress on the interface, producing cracks and detachment of PAM or NAM and reducing the lifetime of the battery. It was found that the Pb-Ca-Sn alloys in 0.5M H2SO4 solution form a multilayer system, verified by the results of EIS and SEM, in which a compact layer of PbO2 and porous layer by PbSO4. Porous layer of PbSO4 was obtained, when the temperature was increased implying greater corrosion kinetics of Pb-Ca-Sn alloy were detected.

Neste trabalho, a influência do aumento da temperatura sobre a taxa de corrosão da liga de Pb-Ca-Sn, o principal componente da grade negativa da bateria de arranque de um carro, foi avaliada por técnicas eletroquímicas: RPL, curvas potenciodinâmica, Tafel e EIS. Por microscopia óptica, SEM- EDS e XRD, os compostos formados nas grades foram caracterizados durante o teste. A camada passiva formada nas grades usadas como cátodo e o ânodo em baterias de chumbo-ácido, permite a âncora na interface de rede-PAM (Material Positivo Ativo) ou NAM (negativo material ativo). Um mau processo de formar esta camada leva ao desenvolvimento de PAM/NAM,conduzindo a falhas prematuras. A temperatura afeta diretamente a cinética de degradação e termodinâmica das reações redox que ocorrem no grade- PAM/NAM sistema. Um aumento da temperatura faz com que as variações na composição química, favorecendo a formação de misturas de óxidos e sulfatos na interface grade-PAM/NAM, o volume e estrutura porosa tornam susceptíveis de falha por stress triaxial na interface, produzindo fissuras e desprendimento do PAM ou NAM e reduzindo o tempo de vida da bateria. Verificou-se que as ligas de Pb-Ca-Sn em solução 0,5M de H2SO4 formar um sistema de múltiplas camadas , a verificação com base nos resultados da EIA e SEM , com as quais foi detectada uma camada compacta de PbO2 e camada porosa PbSO4. Ao aumentar a temperatura de uma camada porosa de PbSO4 foi encontrado, o que implica maiores cinética de corrosão de liga de Pb-Ca-Sn.

El uso de agentes quelantes en procesos de estimulación de pozos de petróleo ha sido propuesto como alternativa al tratamiento ácido cuando el daño de formaciones no permite un ataque químico fuerte. Sin embargo, este procedimiento puede incentivar la corrosión del acero utilizado en la infraestructura de producción de petróleo. En este estudio se evaluó la cinética de corrosión del acero P-110 en fluidos base ácido etildiaminotetraacético (EDTA) en diferentes condiciones. Medidas de polarización lineal fueron realizadas en diferentes regímenes hidrodinámicos y a diferentes temperaturas para evaluar la cinética de corrosión del acero. El electrolito de trabajo consistió en soluciones de EDTA disódico al 10%, y EDTA tetrasódico al 20%. El incremento de la temperatura de 25 a 80°C en ambos electrolitos aumenta la tasa de corrosión del acero en un orden de magnitud, particularmente en soluciones de EDTA-Na2. Las velocidades de corrosión fueron de 0.29x10¹ y 1.67x10² mm·y-1 a 25 y 80°C, respectivamente. El régimen hidrodinámico juega un papel importante solo en la solución disódica, en la cual las velocidades de corrosión se incrementaron a altas velocidades de rotación del electrodo. El efecto de despolarización catódica en la solución de EDTA-Na2es más importante que en la solución de EDTA-Na4, haciéndola más corrosiva.

The use of chelating agents in the oil well stimulation processes has been proposed as an alternative to the acid treatment when the formations damage do not allow the usage of strong chemical attack. However, this procedure can arouse the corrosion of the steel used in the infrastructure of the oil production. In this study, the corrosion kinetics of the P-110 steel in ethylenediaminetetraacetic acid (EDTA) based fluids is assessed under different conditions of evaluation. Linear polarization was performed in different hydrodynamic regimes and at different temperatures, in order to evaluate the kinetic of steel corrosion. The working electrolyte solution comprises 10% disodium EDTA and 20% tetrasodium EDTA. The increase of temperature from 25 to 80°C in both electrolytes increments the corrosion rate of steel in at least one order of magnitude; particularly in EDTA-Na2 solutions. Corrosion rates of 0.29x10¹ and 1.67x10² mm·y-1 were measured at 25 and 80°C, respectively. The hydrodynamic regime plays an important role in the corrosion of steel only in the disodium solution, where corrosion rates were increased at higher rotation speeds of the electrode. The cathodic depolarization effect is more important in the EDTA-Na2 than in the EDTA-Na4solution, making it more corrosive.

O uso de agentes quelantes em processos de estimulação de poços de petróleo foi proposto como alternativa ao tratamento ácido quando o dano de formações não permite um ataque químico forte. Porém, este procedimento pode incentivar a corrosão do aço utilizado na infraestrutura da produção de petróleo. Neste estudo avaliou-se a cinética de corrosão do aço P-110 em fluídos base ácido etilenodiamino tetra-acético (EDTA) em diferentes condições. Medidas de polarização linear foram realizadas em diferentes regimes hidrodinâmicos e a diferentes temperaturas para avaliar a cinética de corrosão do aço. O eletrólito de trabalho consistiu em soluções de EDTA dissódico a 10%, e EDTA tetrassódico a 20%. O aumento da temperatura de 25 a 80°C em ambos os eletrólitos aumenta a taxa de corrosão do aço em uma ordem de magnitude, particularmente em soluções de EDTA-Na2. As velocidades de corrosão foram de 0.29x10¹ e 1.67x10² mm·y-1 a 25 e 80°C, respectivamente. O regime hidrodinâmico joga um papel importante só na solução dissódica, na qual as velocidades de corrosão aumentaram a altas velocidades de rotação do eletrodo. O efeito de despolarização catódica na solução de EDTA-Na2 é mais importante que na solução de EDTA-Na4, fazendo-a mais corrosiva.

The effect of the extract of Lupinus varius l. on corrosion of Al in 1 M NaOH solution using the weight loss technique was investigated. Lupinus varius l. extract inhibited the corrosion of Al in 1 M NaOH solution and the inhibition efficiency increased with increasing the concentration of the extract and decreased with increasing temperature. The adsorption of the inhibitor molecules on Al surface was in accordance with Langmuir and Temkin adsorption isotherms. A first-order kinetic relationship with respect to Al was obtained with and without the extract from the kinetics treatment of the data.

The influence of water-soluble alginates (Alg) and pectates (Pect) anionic polyelectrolytes as natural polymers containing secondary alcoholic groups on the rate of dissolution of aluminum metal in alkaline medium has been investigated by gasometric and weight-loss techniques. The results showed that addition of alginates or pectates to the tested solutions leads to a remarkable decrease in the corrosion rate of Al in NaOH. The magnitude of inhibition efficiency was found to be larger in case of pectates. Factors affecting the corrosion process such as the concentration of the inhibitor and the corrosion medium, structure of the inhibitor and temperature have been examined. The kinetic parameters of corrosion have been evaluated and a suitable mechanism for the inhibition is discussed.