Publication: Diseño y utilización de electrolitos gel para estudios electroquímicos de corrosión en superficies metálicas de geometría compleja
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2018-12
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2018-12-21
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Abstract
La corrosión en uno de los problemas que mayor interés suscita en ingeniería a nivel mundial, y el estudio del comportamiento a corrosión de los materiales durante su vida útil no siempre es una tarea fácil. Los dispositivos que existen comúnmente en el mercado, diseñados para evaluar el comportamiento a corrosión de los materiales emplean electrolitos líquidos, por lo que suelen generar dificultades durante el montaje experimental cuando se intenta delimitar la superficie de ensayo, ya que existe la probabilidad de crear resquicios. Estas zonas son más vulnerables a la aparición de la corrosión y pueden enmascarar los resultados del ensayo. Unido a esta posible interferencia, se encuentran algunas otras dificultades, como el estudio de superficies irregulares, uniones o ángulos poco accesibles, pues los dispositivos usados hasta el momento generalmente están diseñados para el estudio de muestras planas o mecanizables.
En la presente tesis doctoral, se ha desarrollado un electrolito gel a base de agar y glicerol, como alternativa a los electrolitos líquidos utilizados habitualmente en los ensayos electroquímicos, para evaluar el comportamiento a corrosión de los materiales y especialmente en superficies de geometría compleja. El precedente de esta investigación es una novedosa celda portátil con gel de agar como electrolito, diseñada para estudios del patrimonio cultural. A partir de esta propuesta, se decidió mejorar la adaptabilidad del electrolito mediante adiciones de plastificante.
Con el objetivo de determinar la composición óptima del electrolito gel se ha realizado una caracterización de las propiedades físicas variando las concentraciones de agar y glicerol (plastificante). Una vez determinados los porcentajes de estos reactivos que conferían adaptabilidades óptimas al gel, se realizaron ensayos electroquímicos empleando diferentes técnicas y se compararon los resultados con los obtenidos para electrolitos líquidos con las mismas concentraciones de sal e iones despasivantes (Cl¯). Para comprender cómo el empleo de electrolitos gel podía afectar a los mecanismos mediante los cuales transcurre la pasivación y la corrosión, se estudiaron materiales con diferente comportamiento a corrosión, tales como el acero inoxidable, acero al carbono y galvanizado. El uso del electrolito gel también se validó en piezas con geometrías complejas y en diferentes aplicaciones de interés industrial. Además, se profundizó en la influencia de ciertos factores que podían afectar la resistencia a la corrosión acuosa de los materiales tales como la laminación en frío, la formación previa de óxidos a alta temperatura y la radiación γ.
El resultado más relevante de la investigación realizada es la obtención de un electrolito gel con elevada capacidad de deformación sobre superficies metálicas de geometría compleja, con una conductividad similar a la que presentan los electrolitos líquidos tradicionales y que permite obtener resultados comparables y fiables sobre el comportamiento a corrosión de los materiales estudiados. El menor contenido de oxígeno disuelto y la menor difusividad de los cationes metálicos en el gel en comparación con el electrolito líquido parecen afectar moderadamente las reacciones catódica y anódica, disminuyendo la velocidad de corrosión, fundamentalmente en metales activos. Sin embargo, el gel permite obtener información relevante sobre el estado de actividad/pasividad de los metales. Además, el nuevo electrolito gel brinda la posibilidad de monitorizar in situ piezas y estructuras de componentes industriales en servicio.
Corrosion in one of the greatest interest problems in engineering worldwide and to study the corrosion behaviour of materials during their useful life is not an easy task. Commercial devices used to evaluate the corrosion resistance of materials employ liquid electrolytes. However, different difficulties are found during the experimental cell assembly where the surface of the working electrode is delimited, since crevice generation can occur. These areas are more vulnerable to the appearance of corrosion and can mask the results of the test. In addition, these devices only allow studying flat samples, so there are some limitations to study irregular surfaces, joints and not easy accessible angles. In this doctoral thesis a gel electrolyte based on agar and glycerol was developed to evaluate the corrosion behaviour of several materials, especially on surfaces with complex geometry. The precedent of this research was a novel portable cell with agar gel, which was designed to study cultural heritage. Then, it was decided to improve the adaptability of this electrolyte through additions of plasticizer. In order to determine the optimal composition of gel electrolyte, a characterization of physical properties was carried out varying the concentrations of agar and glycerol (plasticizer). Then, electrochemical tests were performed using different techniques and gel electrolytes with the optimal adaptability. The results were compared with those obtained for liquid electrolytes with the same salt concentrations and aggressive ions (Cl¯). Moreover, materials with different corrosion behaviour such as stainless steel, carbon steel and galvanized steel were tested with the aim to understand the corrosion mechanisms in different systems. The use of gel electrolyte was also validated in pieces with complex geometries and in different applications of industrial interest. In addition, the influence of certain factors that can affect the resistance of materials such as cold rolling and oxidation at high temperature and γ radiation were investigated. The most relevant result of this research was to obtain a gel electrolyte with high deformation capacity on metal surfaces with complex geometry. The ionic conductivity of the gel electrolyte is similar to the ionic conductivity of traditional liquid electrolytes. Moreover, comparable and reliable results in terms of corrosion behaviour of the studied materials were reached. The lower content of dissolved oxygen and the lower diffusivity of the metal cations in the gel compared to liquid electrolyte seem to affect moderately the cathodic and anodic reactions mainly in active metals, which also decrease the corrosion rate. However, the gel electrolyte allows obtaining relevant information about the activity/passivity state of metals. In addition, the new gel electrolyte offers the possibility of monitoring in situ parts and structures of industrial components in service.
Corrosion in one of the greatest interest problems in engineering worldwide and to study the corrosion behaviour of materials during their useful life is not an easy task. Commercial devices used to evaluate the corrosion resistance of materials employ liquid electrolytes. However, different difficulties are found during the experimental cell assembly where the surface of the working electrode is delimited, since crevice generation can occur. These areas are more vulnerable to the appearance of corrosion and can mask the results of the test. In addition, these devices only allow studying flat samples, so there are some limitations to study irregular surfaces, joints and not easy accessible angles. In this doctoral thesis a gel electrolyte based on agar and glycerol was developed to evaluate the corrosion behaviour of several materials, especially on surfaces with complex geometry. The precedent of this research was a novel portable cell with agar gel, which was designed to study cultural heritage. Then, it was decided to improve the adaptability of this electrolyte through additions of plasticizer. In order to determine the optimal composition of gel electrolyte, a characterization of physical properties was carried out varying the concentrations of agar and glycerol (plasticizer). Then, electrochemical tests were performed using different techniques and gel electrolytes with the optimal adaptability. The results were compared with those obtained for liquid electrolytes with the same salt concentrations and aggressive ions (Cl¯). Moreover, materials with different corrosion behaviour such as stainless steel, carbon steel and galvanized steel were tested with the aim to understand the corrosion mechanisms in different systems. The use of gel electrolyte was also validated in pieces with complex geometries and in different applications of industrial interest. In addition, the influence of certain factors that can affect the resistance of materials such as cold rolling and oxidation at high temperature and γ radiation were investigated. The most relevant result of this research was to obtain a gel electrolyte with high deformation capacity on metal surfaces with complex geometry. The ionic conductivity of the gel electrolyte is similar to the ionic conductivity of traditional liquid electrolytes. Moreover, comparable and reliable results in terms of corrosion behaviour of the studied materials were reached. The lower content of dissolved oxygen and the lower diffusivity of the metal cations in the gel compared to liquid electrolyte seem to affect moderately the cathodic and anodic reactions mainly in active metals, which also decrease the corrosion rate. However, the gel electrolyte allows obtaining relevant information about the activity/passivity state of metals. In addition, the new gel electrolyte offers the possibility of monitoring in situ parts and structures of industrial components in service.
Description
Mención Internacional en el título de doctor
Keywords
Corrosión, Electrolitos gel, Metales, Análisis termogravimétrico, Electroquímica