The role of the hydrolysis and zirconium concentration on the structure and anticorrosion performances of a hybrid silicate sol-gel coating

Abstract

In sol-gel chemistry, hydrolysis is the key step in the formation of the reactive hydroxide groups that are responsible for the formation of inorganic networks via the occurrence of condensation reactions. Though previous studies have investigated the effect of the hydrolysis conditions on the structure of organically modified silicates (ormosils), no study, to our knowledge, has investigated this variable on the structure of hybrid materials prepared by combinations of an ormosil and a transition metal (TM). Here, we propose to investigate this effect in a hybrid material composed of 3-trimethoxysilylpropylmethacrylate and a zirconium complex. To also highlight the effects of the precursor's concentrations on the hydrolysis and condensation reactions of the hybrid materials, their relative content was altered along with the hydrolysis degree. The anticorrosion barrier properties were identified by characterisation of coatings deposited on AA2024-T3 substrates and correlation between the structure and the anticorrosion properties of the coatings were performed based on results obtained from structural characterisations (DLS, FTIR, 29 Si-NMR, DSC, AFM and SEM) and corrosion testing (EIS and NSS). It is demonstrated that competition in the formation of siloxane and Si-O-Zr bonds takes place and can be controlled by the degree of hydrolysis and the concentration of the zirconium complex. This effect was found to dramatically alter the morphology of the coatings and their subsequent anticorrosion performances. At shortterm exposure times, it is found that the most condensed materials exhibited a higher corrosion resistance while over longer periods the performances were found to level. This article highlighted the critical impact of the hydrolysis degree and zirconium concentration on the connectivity of hybrid sol-gel coatings and the impact this has on corrosion performances.

Abrasion and Cavitation Erosion Resistance of Multi-Layer Dip Coated Sol-Gel Coatings on AA2024-T3

“…Films were prepared with the dip-coating process by withdrawal of substrates from the sol at a controlled speed in the range 100 mm/min. Coated substrates were dried in a hot air oven at 120 • C for 1 h [36]. Substrates were coated using one, two and three dip steps, using the same curing conditions.…”

Characterisation of Holographic Recording in Environmentally Stable Photopolymerisable Glass

“…The sol-gel process employed for PHSG development (as described in Section 2.1) enables the fabrication of nanoparticles from small hybrid molecules. In this process, all small molecules reacted via hydrolysis and condensation reactions to form oligomeric microporous silicate-based nanoparticle systems, as demonstrated by Si-NMR spectroscopy in closely related material systems [24]. Therefore, as a result of thermal curing, the PHSG can be represented as an interconnected network of microporous hybrid silicate and zirconium oxide nanoparticles, where photoinitiator molecules would be able to diffuse and further enable photoreaction processes.…”

Influence of Physical and Mechanical Parameters on Cavitation Erosion and Antifouling Behaviour of Multilayer Silica-Based Hybrid Sol–Gel Coatings on Aluminium Alloys

“…The most commonly used sol-gel formulations for the preparation of hybrid coatings for corrosion protection are derived from the hydrolysis and condensation of semimetal alkoxides, which contain functional groups such as epoxy and methacrylic connected to the central atom by a stable Si-C bond. The formulations involved in the preparations of hybrid coatings to protect the metal substrate from damage are based on the methacrylic group in MAPTMS [32][33][34]. Furthermore, the chemical resistance of these hybrid coatings can be improved by adding more reactive, non-silane alkoxide precursors.…”

“…Physicochemical properties such as morphology and mechanical and surface features that rely on the interactions between TM and silicate precursors are exhibited by the sol-gels prepared from such materials. In addition, the physicochemical properties depend on various factors such as the preparation conditions, pH, rate of hydrolysis, and stabilisation temperature [32].…”