Recubrimientos sol-gel obtenidos por deposición electroforética (EPD) sobre metales

Abstract

El proceso sol-gel es un método de gran interés para la producción de películas vítreas sobre metales, que actúan como barrera protectora frente a la oxidación y aumentan su resistencia a la corrosión. Se han obtenido recubrimientos inorgánicos e híbridos de distintas composiciones sobre distintos metales usando técnicas como inmersión, centrifugado y pulverización. Aunque estos métodos proporcionan recubrimientos con buenas propiedades los espesores obtenidos son bajos (inferiores a 2 mm), lo que limita sus posibilidades de aplicación. La deposición electroforética (EPD) se perfila como una técnica de gran versatilidad para la obtención de recubrimientos homogéneos de mayor espesor. El objetivo de este trabajo es la preparación de recubrimientos sobre metal por EPD a partir de soluciones híbridas de SiO 2 (TEOS, MTES) y de suspensiones coloidales de SiO 2 en las que las propias soluciones híbridas actúan como medio de dispersión. Tanto las soluciones como las suspensiones se han estudiado mediante medidas de viscosidad, densidad y conductividad. Asimismo, se han estudiado los pará-metros físicos asociados a la EPD, tales como el tiempo de deposición y la densidad de corriente, teniendo en cuenta el efecto adicional de formación de capa por inmersión durante la extracción. Los recubrimientos se han caracterizado mediante perfilometría y microscopía óptica, comparando las capas depositadas por inmersión y las obtenidas por EPD. Palabras Clave: Sol-gel, recubrimientos, inmersión, deposición electroforética, sílice coloidal. Sol-gel coatings obtained from electrophoretic depositions (EPD) on metalsSol-gel process is a suitable method for the production of glass-like coatings onto metals, acting as barrier against oxidation and providing an increased resistance to corrosion. Hybrid and inorganic coatings of different compositions have been used for coating several metals by using techniques like dipping, spin-coating and spraying. Although these methods lead to good properties the final coatings are restricted by the thin thickness (up to 2 µm), thus limiting the application range. Electrophoretic deposition (EPD) is considered a highly versatile technique for producing homogeneous thicker coatings. The aim of this work deals with the preparation of coatings onto metals by EPD from hybrid silica sols (TEOS, MTES) and from colloidal silica suspensions where the hybrid sols constitute the suspending medium. Both the solutions and the suspensions have been studied in terms of viscosity, density and conductivity. Furthermore, the physical parameters associated to EPD, such as deposition time and current density, have been also studied, taking into account the additional contribution to the layer formed by EPD occurring by dipping during withdrawal. The coatings obtained by dipping and by EPD have been characterised by perfilometry and optical microscopy.Key words: Sol-gel, coatings, dipping, electrophoretic deposition, colloidal silica. INTRODUCCIÓNLa exposición de metales a condiciones de pH agresivas, a la presencia ...

Transparent SiO2-GdF3 sol–gel nano-glass ceramics for optical applications

“…The incorporation of other silica precursors as methyl triethoxysilane (MTES) that presents an organic radical that remains in the final structure, improves the process, also enhancing the flexibility and avoiding the appearance of cracks in SG materials. This synthesis has been widely used in sol-gel coatings with the aim to increase the thin films thickness [20,21].…”

Thick Sol-Gel Coatings Produced by Electrophoretic Deposition

“…[4,20] The strong conditions imposed by basic catalysis of TMES/TEOS promotes the development of a particulate structure of nano-sized particles, whose concentration depends on the final dilution. Since the isoelectric point of silica in water typically lies at »pH 2, the particles dispersed at pH 9±10 are expected to be negatively charged at the surface and so they should migrate towards the anode, to produce an anodic deposition.…”

Protection and surface modification of metals with sol–gel coatings

“…ZrO 2 -SiO 2 -Na 2 O sols have been prepared under similar basic conditions to those outlined above, which also generated particulate structures. 25,37 These sols were prepared in two steps, prehydrolysis of MTES and TEOS with NaOH, followed by addition of zirconium alkoxide (zirconium(IV) butoxide) complexed with acetyl acetone (AcAc) and water to complete the hydrolysis reaction. The viscosity and stability of these particulate sols were strongly affected by the H 2 O/ (MTESzTEOS) ratio and the total amount of NaOH.…”

“…Rheological measurements showed that these sols exhibited Newtonian behaviour with a viscosity of 2-4 mPa s, depending on the particle concentration. 41 No critical limit was observed in production of films by dipping, up to thicknesses of 4 mm. SiO 2 -ZrO 2 sols from ZrO 2 colloidal suspensions (Nyacol, 20%ZrO 2 , pH 10, particle size 5-10 nm) were obtained by the same procedure, although these were characterised by lower ZrO 2 concentrations, owing to greater dilution of the colloidal suspension.…”

“…SiO 2 -ZrO 2 sols from ZrO 2 colloidal suspensions (Nyacol, 20%ZrO 2 , pH 10, particle size 5-10 nm) were obtained by the same procedure, although these were characterised by lower ZrO 2 concentrations, owing to greater dilution of the colloidal suspension. 37,42 However, the most important characteristic of these suspensions is their ability to be deposited by EPD. Sols prepared under acidic catalysis from TEOS/MPS and colloidal silica (40-70 wt-%) were stable, despite the high content of water in the final suspension.…”