Publication: Nuevos recubrimientos híbridos SOL-GEL libres de cromatos con altas prestaciones anticorrosivas
Loading...
Identifiers
Publication date
2020-05
Defense date
2020-05-14
Authors
Advisors
Tutors
Journal Title
Journal ISSN
Volume Title
Publisher
Impact
Export
Abstract
La protección de los materiales metálicos frente a su degradación, por efecto de la corrosión, es uno de los principales objetivos en el campo de ingeniería de materiales a nivel industrial. Tradicionalmente, los cromatos hexavalentes se han empleado como anticorrosivos debido a su buena relación coste/efectividad. Sin embargo, la alta toxicidad asociada a estos compuestos implica considerables riesgos para el medio ambiente y la salud de los trabajadores. Como consecuencia, las políticas de restricción que limitan el empleo de los cromatos hexavalentes han aumentado, llegando en muchos sectores a prohibir su uso por completo.
Esta situación ha suscitado la aparición de un nuevo campo de investigación centrado en fomentar alternativas más ecológicas, para la protección de sustratos metálicos frente al proceso de corrosión. Una posible solución podría basarse en los recubrimientos híbridos organo-inorgánicos sintetizados a través de la tecnología sol-gel. En esta Tesis Doctoral se han diseñado y desarrollado recubrimientos sol-gel con propiedades anticorrosivas como imprimación para sustratos de acero al carbono. La funcionalización de estos materiales se ha llevado a cabo modificando la síntesis mediante la adición de compuestos, inhibidores del proceso de corrosión, de forma directa o bien encapsulados en la estructura de sílices mesoporosas. Los inhibidores encapsulados, insertados en los recubrimientos, tienen como objetivo aumentar su tiempo de vida mediante la liberación controlada al medio.
Para llevar a cabo este proyecto, en primer lugar, se ha optimizado el proceso sol-gel con el fin de obtener una matriz control con unas propiedades adecuadas para formar un film homogéneo, libre de grietas y con buena adherencia al sustrato. La segunda parte del proyecto se ha centrado en la funcionalización del material control, mediante la adición de inhibidores de la corrosión atrapados en la red intermolecular del recubrimiento. Se han evaluado tres porcentajes de inhibidores y uno de ellos ha sido seleccionado como óptimo para una adecuada protección. De forma paralela se ha llevado a cabo la inserción de iones de cerio (III), (conocidos por su inhibición catódica), en el espacio interlaminar de la estructura de un filosilicato denominado montmorillonita (MMT) empleando el método de intercambio iónico. Por último, la matriz sol-gel control se ha funcionalizado añadiendo partículas de arcilla dopadas con cerio y partículas de arcilla sin dopar en dos concentraciones distintas.
Finalmente, se obtiene la evaluación de los recubrimientos a través de una caracterización fisicoquímica, la cual se complementa con un profundo estudio electroquímico mediante el empleo de técnicas tanto generales como locales. Como resultado destaca la mejora de las propiedades barrera del sol-gel dopado con cerio, así como su protección contra la corrosión.
The protection of metallic materials against degradation, due to corrosion effect, is one of the main objectives on the field of materials engineering at the industrial scale. Traditionally, hexavalent chromates have been used as anticorrosive agent as a result of the optimal cost-effective relation. However, the high toxicity associated to these compounds implies considerable risks for the environment and workers´ health. As a consequence, the restriction policies that limit the use of hexavalent chromates have increased, causing many sectors to ban their use. This situation has led to the rise of a new research field, focused on promoting greener alternatives for the protection of metal substrates against corrosion process. Organo-inorganic hybrid coatings synthesized through sol-gel technology are one of the most promising materials. In this Doctoral Thesis, sol-gel coatings with anticorrosive properties have been designed and developed as a primer for carbon steel substrates. The functionalization of these materials has been carried out by modifying the synthesis process through the addition of compounds with inhibitory properties. This compound can be added directly, or can be encapsulated in the structure of mesoporous silicas. The aim of this last strategy is focused on the life time inhibitors increase by controlling the release into the medium. To perform this project, the sol-gel process has been optimized. In first place by obtaining a control matrix with suitable properties (homogeneous, crack-free film with proper adhesion to the substrate). Then, the project has been focused on the functionalization of the control material by adding corrosion inhibitors trapped in the intermolecular network coating. Three percentages of inhibitors have been evaluated and one of them has been selected as optimal for adequate protection. In parallel, the insertion of cerium (III) ions, (cationic inhibition), has been carried out in the interlaminar space of the structure of a phyllosilicate called montmorillonite (MMT) using the ion exchange method. Finally, the sol-gel control matrix has been functionalized by adding doped cerium-clay particles and undoped clay particles in two different concentrations. Eventually, the evaluation of the selected coatings is obtained through a physicochemical characterization, which is complemented by a deep electrochemical study through the use of general and local techniques. As a result, cerium doped sol-gel improves the barrier proprieties as well as its protection against corrosion.
The protection of metallic materials against degradation, due to corrosion effect, is one of the main objectives on the field of materials engineering at the industrial scale. Traditionally, hexavalent chromates have been used as anticorrosive agent as a result of the optimal cost-effective relation. However, the high toxicity associated to these compounds implies considerable risks for the environment and workers´ health. As a consequence, the restriction policies that limit the use of hexavalent chromates have increased, causing many sectors to ban their use. This situation has led to the rise of a new research field, focused on promoting greener alternatives for the protection of metal substrates against corrosion process. Organo-inorganic hybrid coatings synthesized through sol-gel technology are one of the most promising materials. In this Doctoral Thesis, sol-gel coatings with anticorrosive properties have been designed and developed as a primer for carbon steel substrates. The functionalization of these materials has been carried out by modifying the synthesis process through the addition of compounds with inhibitory properties. This compound can be added directly, or can be encapsulated in the structure of mesoporous silicas. The aim of this last strategy is focused on the life time inhibitors increase by controlling the release into the medium. To perform this project, the sol-gel process has been optimized. In first place by obtaining a control matrix with suitable properties (homogeneous, crack-free film with proper adhesion to the substrate). Then, the project has been focused on the functionalization of the control material by adding corrosion inhibitors trapped in the intermolecular network coating. Three percentages of inhibitors have been evaluated and one of them has been selected as optimal for adequate protection. In parallel, the insertion of cerium (III) ions, (cationic inhibition), has been carried out in the interlaminar space of the structure of a phyllosilicate called montmorillonite (MMT) using the ion exchange method. Finally, the sol-gel control matrix has been functionalized by adding doped cerium-clay particles and undoped clay particles in two different concentrations. Eventually, the evaluation of the selected coatings is obtained through a physicochemical characterization, which is complemented by a deep electrochemical study through the use of general and local techniques. As a result, cerium doped sol-gel improves the barrier proprieties as well as its protection against corrosion.
Description
Mención Internacional en el título de doctor
Keywords
Metales, Materiales de recubrimiento, Corrosión, Sol-gel, Coatings, Steel