Organic-Inorganic Hybrid Coatings for Corrosion Protection of Metallic Surfaces

Abstract

A variety of organic-inorganic hybrids have been designed to act as anticorrosive coatings of metallic substrates. Among them, epoxy-silica and poly(methyl methacrylate) (PMMA)-silica hybrids, prepared by the sol-gel process and deposited onto steel or aluminum alloys, have demonstrated high anticorrosive efficiency combined with high thermal and mechanical resistance. Lignin, carbon nanotubes, and graphene oxide have been incorporated into PMMA-silica hybrids as reinforcement agents, and cerium (IV) as corrosion inhibitor. Both hybrids were characterized in terms of their structural and thermal characteristics using different pectroscopies, microscopies and thermogravimetric analysis. Both hybrids present homogeneous nanostructure composed of highly condensed silica nanodomains covalently bonded to the polymeric phase. The transparent coatings with a thickness of 2-7 μm have low surface roughness, high adhesion to metallic substrates, elevated thermal stability, and excellent barrier behavior. Electrochemical impedance spectroscopy showed for coated samples a high corrosion resistance of up to 50 GΩ cm2 and durability >18 months in saline solution. Further improvement of corrosion resistance, thermal and mechanical stability was achieved by incorporation of lignin, carbon nanotubes, and graphene oxide into PMMA-silica matrix, and a self-healing effect was observed after Ce(IV) addition. The results are compared and discussed with those recently reported for a variety of hybrid coatings.

Sacrificial Thermally Sprayed Aluminium Coatings for Marine Environments: A Review

“…Protective coatings can be divided into: inorganic (for example ceramic (e.g., alumina) or carbon coatings), organic (such as epoxy and polyurethane), organic-inorganic hybrids (also known as smart or functionalised coatings), and metallic coatings [4]. Depending on the electrode potential with respect to the substrate metal (usually steel), metallic coatings can be formed either anodic (e.g., aluminium and zinc) or cathodic (e.g., nickel and copper).…”

Organic-Inorganic Hybrid Coatings for Active and Passive Corrosion Protection

“…The development of efficient production techniques of metallic alloys in the late twentieth century formed the basis for the boom of construction, transportation, energy, packaging, and electronic industries [1,2]. Although extensively used, unprotected alloys are subject to a constant oxidation process, either in contact with humid atmosphere, aqueous, or soil systems, turning them into natural ore [1,3]. One common approach to prevent or at least delay metallic corrosion is the application of organic coatings as a physical diffusion barrier.…”

“…One promising class of coating systems, developed in the last decade, which fulfill the cited criteria, is organic-inorganic nanocomposites based on conventional acrylic, epoxy, and polyurethane materials combined with ceramic nanofillers, such as silica, ceria, zirconia, etc. These hybrid materials have demonstrated excellent barrier property, providing long-term protection for steel and aluminum alloys [3,[8][9][10]. The superiority of hybrid systems compared to purely polymeric phases comes from a tailored nanostructure achieved by proper amounts of inorganic nanofillers within the organic matrix and the careful tuning of synthesis conditions, resulting in a dense and homogeneous nanocomposite that acts as an efficient diffusion barrier, limiting the water uptake and diffusion of ionic species to a very low rate [11].…”

“…The inorganic nodes have the important role to densify the structure by anchoring covalently the polymeric chain segments through a cross-linking agent and to improve the adhesion at the coating/metal interface through covalent bonding [12][13][14]. The function of the polymeric phase is to provide minimum internal stress and porosity of the hybrid network, hermetically sealing the structure [3,11,12]. Hence, the key factor for the stability of the material under adverse conditions is the covalent conjugation between the two phases through the coupling molecule that has functional similarity to both parts.…”

“…Several approaches have been developed in the search for chromium-free organic coatings using organic and inorganic additives for extrinsic self-healing strategies. These types of coatings are able to respond after local damage through reactions triggered by variations in pH, temperature, presence of water, mechanical damage, and UV [3,4,19].…”