Abstract
This work investigates the role of the structure of a zirconium complex (ZC) on the condensation and anticorrosion properties of an organosilane sol-gel coating. The structure and reactivity of the ZC were modified by varying the content of methacrylic acid employed as a chelating agent. The structures of the developed materials were characterised by Dynamic Light Scattering, Fourier Transform Infrared Spectroscopy, Differential Scanning Calorimetry and Scanning Electron Microscopy. The passive anticorrosion properties were evaluated by Electrochemical Impedance Spectroscopy of the sol-gel coatings deposited on AA2024-T3 substrates. It was highlighted, that a competition in the condensation process of the silicate (Si-O-Si) and silicon-ZC oxides (Si-O-Zr) species can be tailored by the structure of the ZC, with the least chelated ZC exhibiting the highest content of Si-O-Zr bonds. At the same time, it was also found that the coatings containing the highest content of Si-O-Zr groups exhibited the best anticorrosion barrier performances amongst all sol-gel coatings investigated here, therefore presenting the highest condensation degree. This suggested that Si-O-Zr bonds were the essential chemical species responsible for the formation of condensed coatings. A direct correlation between the structure of the coatings and their anticorrosion performances is proposed.
Highlights
As all coatings were prepared after 1 day of ageing, it was useful to get a picture of the particle size of all material systems on day 1 to identify if this parameter can be correlated to the subsequent structural properties and the coatings’ anticorrosion properties
This work aimed at identifying the effect of the chelating agent on the structure and anticorrosion properties of hybrid sol-gel materials composed of both silicon and zirconium alkoxides
The formation of covalent silicon-zirconium oxides (Si-O-Zr) bonds is found to be favoured by the decrease of chelation, essentially due to the increase of reactive zirconium groups
Summary
These processes include anodization, passivation, chemical conversion, ion implantation, cathodic electrodeposition and sol-gel coatings They are based on the use of individual chemistries such as trivalent chromium, phosphate, zinc phosphate, permanganate, rare earth metals, vanadium or combinations of these different compounds. Mercaptosilanes have been used to functionalise glass surfaces for the immobilisation of biological species [8], epoxysilanes have been employed to improve the adhesion properties of organic coatings [9] and acryloxysilanes have been used to provide photoreactivity for the fabrication of miniature devices [10] and microstructuring of optical devices [11] These organosilane sol-gel matrices are capable of hosting organic and inorganic doping elements to further provide desirable characteristics for specific applications. Network modifiers such as transition metal alkoxides or ionic liquids have been incorporated within silicate-based materials to adjust the optical [16] [17], electrical [18] or surface morphology of inorganic surfaces [19]
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