Improved mechanical and anticorrosion properties of metal oxide-loaded hybrid sol–gel coatings for mild steel in a saline medium

Abstract

A hybrid organic–inorganic sol–gel coating was successfully prepared and subsequently functionalized individually with five different metal oxide additives. The effect of the incorporated oxides on the corrosion protection performance and scratch-resistance properties of the hybrid base coating on mild steel substrates was investigated using electrochemical techniques, namely electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) as well as mechanical testing. The steel-coated specimens were immersed in 3.5?wt.% NaCl corrosive medium for two weeks and the results reveal an excellent corrosion protection performance by all coating formulations with a significant high corrosion-resistance property for the sample loaded with molybdenum oxide. Scanning electron microscopy (SEM) images proved the absence of corrosion signs, defects, micro cracks, or delamination on the surface of the coated samples. Compared with the pure hybrid coating, all the metal oxide-embedded coatings (except for the sample loaded with yttrium(III) oxide) show comparable aqueous contact angle values as well as enhanced hardness and adherence properties. No noticeable dependence was observed for the surface roughness parameters as a function of the type of incorporated metal oxide within the sol–gel matrix. Overall, the results of this study demonstrate that metal oxides can be advantageous to the desired properties of hybrid sol–gel coatings applied to steel surfaces.     

Hybrid organosiloxane coatings containing epoxide precursors for protecting mild steel against corrosion in a saline medium

Hybrid organic–inorganic materials made from sol–gel precursors can be used as anticorrosion barriers on metal substrates. The modification of epoxy resins with silicones is an interesting approach toward the synthesis of hybrid materials that combine the advantages offered by epoxy resins with those of silicones. In this study, novel hybrid epoxy‐silicon materials were synthesized using sol–gel chemistry and subsequently functionalized with 4,4′‐methylenebis(phenyl isocyanate), incorporating urethane functionality into the final polymer. The study screened five different epoxide precursors for use in the synthesis of the new hybrid materials and optimizing their anticorrosion properties. Spectral characterization confirms the proposed chemical structures of the newly synthesized polymers. The newly developed polymers were painted on mild steel panels, thermally cured, and their thermal, surface morphological, adhesion, and anticorrosion properties were fully characterized. The new coatings were found to have excellent thermal stability and adherence properties to steel surface. The results of corrosion testing on coated steel panels following long‐term immersion in a 3.5 wt % aqueous NaCl medium revealed that the polymer prepared using the epoxide precursor bisphenol A diglycidyl ether provided the best anticorrosion protection property among the synthesized polymers. This could be attributed to the excellent integrity and crosslink density properties in addition to the lack of microdefects in the surface of this coated sample as confirmed by scanning electron microscopy analyses. The newly prepared hybrid coatings reported in this study are very promising as an alternative to toxic chromate‐based coatings. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43947.     

UV‐curable sol–gel based protective hybrid coatings

UV‐curable, novel, fluorinated polyether ether ketone urethane acrylate oligomer (FPEEKUA) has been synthesized and used as corrosion‐protector in sol–gel hybrid coatings for metallic substrates. Incorporation of FPEEKUA and sol–gel in the formulations improved coatings’ physical properties such as gel content, hardness, adhesion, gloss, flexibility, and contact angle. Due to strong interaction between acrylate and highly crosslinked structures, mechanical properties improved drastically with homogenously dispersed structures throughout the organic matrix, while water uptake values decreased and thermal stability and char yields increased. Highest contact angle values were measured up to 94° with shinny coatings. The results are important for two reasons. First, polyether ether ketone (PEEK) immiscibility problem are overcome by using reactive oligomer and benefitted from high performance properties of poly(arylene ether ketones) (PAEK)s in hybride coating applications. Second, Coatings combine the advantages of sol–gel with poly(arylene ether ketone urethane acrylate) (PAEKUA) oligomer and they can be used as barrier coatings in metal corrosion protection. Performance tests in corrosive mediums at room temperature of chlorine solution (bleach) for 24 h and also in a 10 wt% HCl solution for 92 h produced promising results for use in corrosion mitigation applications in highly corrosive downstream oil and gas industry. POLYM. ENG. SCI., 59:E146–E154, 2019. © 2018 Society of Plastics Engineers     

Electrochemical investigations on the corrosion protection effect of poly(vinyl carbazole)‐silica hybrid sol–gel materials

A series of sol–gel derived organic–inorganic hybrid coatings consisting of organic poly (vinyl carbazole) (PVK) and inorganic silica (SiO₂), with 3‐(trimethoxysilyl)propyl methacrylate (MSMA) as coupling agent, were successfully synthesized. First of all, vinyl carbazole (VCz) monomers are copolymerized with MSMA by performing free‐radical polymerization reactions with AIBN as initiator. Subsequently, as‐prepared copolymer (i.e., sol–gel precursor) was further reacted with various feeding content of tetraethyl orthosilicate (TEOS) through organic acid (CSA)‐catalyzed sol–gel reaction to form a series of PVK‐silica hybrid (PSH) sol–gel materials. The as‐synthesized hybrid materials were subsequently characterized by Fourier‐Transformation infrared (FTIR) spectroscopy and solid‐state ²⁹Si NMR. It should be noted that the PVK‐SiO₂ hybrid (PSH) coating on cold‐rolled steel (CRS) electrode with low silica loading (e.g., 10 phr) was found to be superior in anticorrosion property over those of neat PVK based on a series of electrochemical measurements such as corrosion potential, polarization resistance, corrosion current, and electrochemical impedance spectroscopy in 3.5 wt% NaCl electrolyte. The better anticorrosion performance of PSH coatings as compared to that of neat polymer may probably be attributed to the stronger adhesion strength of PSH coatings on CRS electrode, which was further evidenced by Scotch tape test evaluation. Increase of adhesion strength of PSH coatings on CRS electrode may be associated with the formation of Fe–O–Si covalent bonds at the interface of PSH coating and CRS electrode based on the FTIR–RAS (reflection absorption spectroscopy) studies. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Anticorrosive behavior study by localized electrochemical techniques of sol–gel coatings loaded with smart nanocontainers

In the present work, sodium phosphomolybdate, an environmentally friendly corrosion inhibitor with good anticorrosive behavior when applied on steel substrates, has been loaded and encapsulated in mesoporous silica nanoparticles without and with a hollow core in order to produce different smart nanocontainers. These nanocontainers have been designed to allow controlled release of the inhibitor in response to an external stimulus, thereby achieving more efficient and more economical use of the active substance. Corrosion activity leads to local changes in pH, and this work considers such changes as a signal of great interest. The nanocontainers respond to a pH of 10 or higher by increasing the release rate of the encapsulated active material. The smart nanocontainers have been incorporated into hybrid organic–inorganic sol–gel coatings and applied on carbon steel substrates. Mechanical defects have been made in the organic coating, reaching through to the metallic substrate, in order to study anticorrosive behavior in the affected area. A characterization study has been carried out at the defects and in their surroundings by means of two different localized electrochemical techniques: Scanning Kelvin Probe and Localized Electrochemical Impedance Spectroscopy. The results have shown significant improvement in the anticorrosive behavior of sol–gel coatings when formulated with smart nanocontainers loaded with sodium phosphomolybdate compared to a reference sol–gel coating.     

Enhancement of corrosion protection of mild steel by chitosan/ZnO nanoparticle composite membranes

The development of active corrosion protection systems for metallic substrates is an issue of prime importance for many industrial applications. Nanostructured chitosan/ZnO nanoparticle films were coated on mild steel by sol–gel process, dip coating technique. Sol–gel protective coatings have shown excellent chemical stability, oxidation control and enhanced corrosion resistance for metal substrates. Further, the sol–gel method is an environmentally friendly technique of surface protection which has traditionally been used for increasing corrosion resistance of metals. Films so formed were characterized by UV–vis absorption spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray fluorescence spectrometry (EDX). Corrosion protection behavior of these coated mild steel substrates in 0.1 N HCl solutions was evaluated by potentiodynamic polarisation studies (Tafel), linear polarisation studies (LPR), electrochemical impedance spectroscopy studies (EIS).     

Corrosion protection of aluminum alloy substrate with nano-silica reinforced organic–inorganic hybrid coatings

Organic–inorganic hybrid (OIH) thin films derived from the sol–gel process have emerged as sustainable metal pretreatment alternatives to toxic heavy metal-based systems. In recent years, such OIH systems based on Si, Zr, and Ti have been successfully developed and commercialized for pretreatment of aluminum alloys, galvanized steel, cold-rolled steel, and many other metals and alloys, for improving adhesion and corrosion resistance performance. A variety of approaches are being used to further enhance performance of such OIH systems to match or surpass that obtained from chromate-based systems. In the present study, a novel bis-silane compound has been synthesized and used as a primary sol–gel precursor for OIH coatings. In order to further improve their mechanical and corrosion resistance performance, colloidal nanoparticles have been incorporated. The microstructure of the deposited films as a function of their composition and formation of Si–O–Si structural network has been studied by Confocal Raman spectroscopic technique. The chemical structure of the OIH films has been characterized by FTIR analysis. Electrochemical impedance spectroscopy, DC polarization measurements, and accelerated neutral salt-fog test (ASTM B117) have been used to evaluate corrosion resistance performance of coatings on industrial aluminum alloy AA 3003 H14. Nano-indentation tests of these OIH films have been performed to study the effect of colloidal nanoparticles on coating micro/nano structure and their mechanical properties. The study reveals that colloidal nanoparticles improve the corrosion resistance of OIH coatings by formation of a protective barrier to diffusion of corrosive species to the metal surface. The optimum content of colloidal nanoparticles that can provide best corrosion protection has been determined. Electrochemical study provides useful insight into the significance of interaction between the sol–gel hybrid and silica particles in the corrosion protection mechanism.     

Enhancement of corrosion protection of 3-glycidoxypropyltrimethoxysilane-based sol–gel coating through methylthiourea doping

Protection of aluminum metal and its alloys from corrosion is a key requirement for many engineering applications. Nowadays, sol–gel coating technology is recognized as the ideal replacement for chromate conversion coatings. The present work makes use of 3-glycidoxypropyltrimethoxysilane (GPTMS) as a precursor for sol–gel coating. GPTMS was subjected to hydrolysis and subsequent condensation reaction to get a three-dimensional network and methylthiourea (MTU) was incorporated into the sol–gel matrix. MTU-doped GPTMS-based sol–gel coatings were applied over aluminum metal by dip coating method. The resultant coating was studied by FTIR, XRD and SEM. MTU-doped GPTMS-based sol–gel coatings increased the hydrophobic nature of the coating and were stable up to a temperature of 450°C. The protective nature of the coatings was evaluated in a 1% NaCl environment using electrochemical impedance and polarization studies. The study has revealed that doping of MTU enhanced the protection ability of doped GPTMS-based sol–gel coating to a significant extent.     

Synthesis and characterization of flame retarding UV‐curable organic–inorganic hybrid coatings

UV‐curable, organic–inorganic hybrid materials were synthesized via sol–gel reactions for tetraethylorthosilicate, and methacryloxypropyl trimethoxysilane in the presence of the acrylated phenylphosphine oxide resin (APPO) and a bisphenol‐A‐based epoxy acrylate resin. The sol–gel precursor content in the hybrid coatings was varied from 0 to 30 wt %. The adhesion, flexibility, and hardness of the coatings were characterized. The influences of the amounts of inorganic component incorporated into the coatings were studied. Results from the mechanical measurements show that the properties of hybrid coatings improve with the increase in sol–gel precursor content. In addition, thermal properties of the hybrids were studied by thermogravimetric analysis in air atmosphere. The char yield of pure organic coating was 32% and that of 30 wt % silicate containing hybrid coating was 30% at 500°C in air atmosphere. This result demonstrates the pronounced effect of APPO on the flame retardance of coatings. Gas chromatography/mass spectrometry analyses showed that the initial weight loss obtained in thermogravimetric analysis is due to the degradation products of the photoinitator and the reactive diluent. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1906–1914, 2006     

Inorganic/organic hybrid coatings for aircraft aluminum alloy substrates

A series of water-based stable sol–gel systems have been developed. Various functional groups including amino, epoxy, vinyl, and allyl groups can be incorporated into the sol–gel network to interact with organic polymer resins. The solid content of these sol–gel-based coating formulations varies from 2.5 to 45%. The sol–gel coating of alumina–silica networks derived from low solid content solutions (2.5%) has been developed and evaluated to replace the current conversion coating pretreatment process. Sol–gel coatings derived from the high solid content solutions (17–45%) have shown excellent mechanic strength, good adhesion, and provide corrosion protection of the aluminum substrate when cured at elevated temperatures. Sol–gel/epoxy resin hybrid coatings have been formulated and studied. The hybrid coating showed enhanced mechanical strength such as hardness and abrasion resistance. When cured at elevated temperatures (80°C), all of the hybrid coatings studied passed wet adhesion testing. Some of the hybrid coatings pass wet adhesion testing when cured at room temperature. However, water-sensitivity remains for most of the room temperature cured hybrid coatings.     

Preparation and anticorrosive properties of hybrid coatings based on epoxy‐silica hybrid materials

A series of sol‐gel derived organic–inorganic hybrid coatings consisting of organic epoxy resin and inorganic silica were successfully synthesized through sol‐gel approach by using 3‐glycidoxypropyl‐trimethoxysilane as coupling agent. Transparent organic–inorganic hybrid sol‐gel coatings with different contents of silica were always achieved. The hybrid sol‐gel coatings with low silica loading on cold‐rolled steel coupons were found much superior improvement in anticorrosion efficiently. The as‐synthesized hybrid sol‐gel materials were characterized by Fourier‐transformation infrared spectroscopy, ²⁹Si‐nuclear magnetic resonance spectroscopy and transmission electron microscopy. Effects of the material composition of epoxy resins along with hybrid materials on the thermal stability, Viscoelasticity properties and surface morphology were also studied, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The effect of zirconia ions on corrosion performance of sol–gel coated galvanized steel

Currently, galvanized steel is treated with hexavalent chrome passivation. Sol–gel coating has been found to be a potential replacement for the hazardous hexavalent chrome passivation treatment. The aim of this work is to study the effect of zirconyl nitrate on corrosion behavior of sol–gel coating. Aminopropyl-trimethoxysilane and 3-glycidoxypropyltrimethoxysilane were employed as precursors to prepare the sol–gel-based silane coating. The sol–gel film was deposited on galvanized steel sheet by dip coating method. The chemical properties of sol–gel solution and coated films were analyzed by infrared spectroscopy. Morphology of the film was characterized by scanning electron microscope. The corrosion resistance of the coated samples was evaluated by electrochemical impedance spectroscopy, potentiodynamic polarization curve, and salt spray test. The results indicated that zirconia-doped coatings have better corrosion resistance in comparison with their undoped counterparts. The coating doped with 0.5% zirconyl nitrate provides better corrosion protection due to the inhibitive action of zirconia ion.     

Study the factors affecting the performance of organic–inorganic hybrid coatings

In this article, a series of hybrid organic–inorganic coatings based on silica‐epoxy composite resins were prepared with the sol‐gel method by using γ‐aminopropyl triethoxysilane as a coupling agent. Especially, the research emphasized on the factors that influenced on the properties of the prepared hybrid coatings. Firstly, epoxy resin was reacted with γ‐aminopropyl triethoxysilane at a specific feeding molar ratio; subsequently, the asprepared sol–gel precursor was cohydrolyzed with tetraethoxysilane (TEOS) at various contents to afford chemical bondings to form silica networks and give a series of organic–inorganic hybrid coatings. They were loaded and cured on steel panels and characterized for FTIR, TGA, DSC, water contact angles (WCA), pencil hardness, surface & three‐dimensional morphological studies, and potentiodynamic polarization tests. The surfaces of the hybrid coatings showed Sea‐Island or Inverting Sea‐Island morphologies at a certain relative content of two components, which made the coatings possess hydrophobic property. Due to the contribution of organic and inorganic components, the prepared hybrid coatings possess a lot of properties such as pencil hardness, thermotolerance, and corrosion resistance. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41010.     

Nanostructured sol–gel derived conversion coatings based on epoxy- and amino-silanes

Inorganic/organic hybrid conversion surface coatings for long-term protection of aluminum alloys against atmospheric corrosion have been developed based on a unique self-assembled nanophase particle (SNAP) coating process. Nano-particles with peripheral epoxy functional groups are pre-formed in an aqueous sol–gel process and then assembled and crosslinked upon application on the substrate surface. Mono-, di-, and tri-functional amino-silanes have been used as crosslinking agents. Corrosion resistance properties of these hybrid nanocomposite coatings studied by a variety of electrochemical testing methods including electrochemical impedance spectroscopy, scanning vibrating electrode technique, and potentiodynamic scan method, indicate excellent barrier protection performance of the coatings. For comparison, coatings crosslinked with amino-silanes offer significant improvement in coating performance over the previously described SNAP formulations with a conventional amine crosslinker—diethylenetriamine.     

Hybrid nanocomposite coating by sol–gel method: a review

The development of environmentally friendly process for pretreatments of metallic substrates is a field of growing research due to the ban against chromates used as protective pretreatments. Among the possible candidates for environmentally friendly pretreatments of aluminum alloys are the silica-based sol–gel coatings. Such coatings are able to form an Si–O–Al conversion layer providing a stable alumina/sol–gel film interface, which inhibits the onset of corrosion. Sol–gel technology offers a wide range of chemical mechanisms and exhibits high potential substitutes for the environmentally unfriendly chromate metal-surface pretreatment. Sol–gel derived organo-silicate hybrid coatings, preloaded with organic corrosion inhibitors, have been developed to provide active corrosion protection when integrity of the coating is compromised. The incorporation of organic corrosion inhibitors into hybrid coatings has been achieved as a result of physical entrapment of the inhibitor within the coating material at the stage of film formation and cross-linking. Sol–gel derived coatings, especially the hybrid films, provide a dense barrier against electrolyte uptake, and offer a wide range of applications as corrosion protective, hydrophilic coatings, hydrophobic anti-reflective coatings, migration barriers against liquid and volatile compounds, antibacterial modification of textiles and water-repellent antistatic textiles. In this paper, the novel applications of the sol–gel derived coatings are presented and discussed.     

Hard coatings on polycarbonate plate by sol‐gel reactions of melamine derivative,PHEMA, and silicates

Hard coatings were deposited on a polycarbonate plate using a sol‐gel process with a melamine derivative, PHEMA, and silicates, and examined as potential substitutes for glass in cars. Poly(2‐hydroxyethyl methacrylate) was partially functionalized with (3‐isocyanatopropyl)triethoxysilane, and the synthesized polymer was used to form a coating solution with methylated poly(melamine‐co‐formaldehyde), tetraethoxysilane, and methyltriethoxysilane. The coatings on the polycarbonate plate were deposited using a sol‐gel process. Precoating with poly(methyl methacrylate) was carried out to improve the adhesive strength of the coating. The optimum conditions and formulation to obtain excellent physical properties of the coating were determined. Smooth coatings with the hardness of a 3H class pencil, excellent abrasion resistance, and transparency were formed. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

The corrosion resistance of 316L stainless steel coated with a silane hybrid nanocomposite coating

The present work aims at evaluating the corrosion resistance of 316L stainless steel pre-treated with an organic–inorganic silane hybrid coating. The latter was prepared via a sol–gel process using 3-glycidoxypropyl-trimethoxysilane as a precursor and bisphenol A as a cross-linking agent. The corrosion resistance of the pre-treated substrates was evaluated by neutral salt spray tests, linear sweep voltammetry and electrochemical impedance spectroscopy techniques during immersion in a 3.5% NaCl solution. In addition, the effect of the drying method as an effective parameter on the microscopic features of the hybrid coatings was studied using Fourier transform infrared spectroscopy and scanning electron microscopy. Results show that the silane hybrid coatings provide a good coverage and an additional corrosion protection of the 316L substrate.     

Hard coatings on polycarbonate plate by sol–gel reactions of melamine derivative,poly(vinyl alcohol), and silicates

Hard coatings were deposited on a polycarbonate plate using a sol–gel process with a melamine derivative, poly(vinyl alcohol) (PVA), and silicates and examined as potential substitutes for glass in cars. PVA was partially functionalized with (3-isocyanatopropyl)triethoxysilane, and the synthesized polymer was used to form a coating solution with methylated poly(melamine-co-formaldehyde), tetraethoxysilane, and methyltriethoxysilane. The coatings that contained both the melamine and silicate structures were deposited using a sol–gel process. The optimum conditions and formulation to obtain excellent physical properties of the coating were determined. Smooth coatings with the hardness of a 3H class pencil, excellent abrasion resistance and transparency were formed.     

In-situ generation and application of nanocomposites on steel surface for anti-corrosion coating

Thin organic coatings directly on steel sheets provide excellent barrier protection in saline environment and meet deformability demands, but fail in providing active corrosion protection. We have put an effort to solve this problem by formulating composite coatings using in-situ generation of metal oxide nanoparticles (NPs) in the polymer matrix. Here we present a new synthesis method of high performance polyetherimide composite with TiO₂, MgO, and Al₂O₃ nanoparticles and their application for anti-corrosion coatings in saline environment. We observed that in-situ synthesis of these metal oxide NPs in the polymer curing process leads to evenly distribution and uniform size of nanoparticles. Thermo-mechanical property was analyzed for these three kinds of free-standing composite film to assess elasto-plastic behaviour and compared to mother polymer film. Results indicated that thermal stability and elastic behaviour of composites film are not affected to the great extent by the presence of NPs. The potentiodynamic and the electrochemical impedance studies on these composite coated steel panels were carried out to identify active–passive behaviour. Results showed active corrosion protection from nanocomposite coating based on TiO₂ and barrier protection was noticed from nanocomposite coating based on MgO and Al₂O₃.     

Investigation of the mechanical and thermal fatigue properties of hybrid sol–gel coatings applied to AA2024 substrates

This research article reports on the response of various hybrid sol–gel materials when applied as coatings to pre-treated bare AA2024 substrates, to mechanical indentation and cyclic thermal stimuli, in order to determine their usefulness in aeronautical applications. Three groups of hybrid sol–gel-coated samples were prepared using various organosilanes and transition metal oxides. The characterization of the materials revealed that the presence of the organic functionalities, especially the methacrylate group, has a noticeable effect on the mechanical response of the hybrid coatings, in particular their flexibility. The presence of methacrylate group in the cured material gives it ability to flex which influenced the thermal fatigue characteristics of the coatings which are able to withstand the cyclic temperature regimes of 82 ± 3 to ?37 ± 3°C over 25 2 h cycles. This capability to maintain substrate protection is reflected in the corrosion resistance of the coatings as measured using electrochemical impedance spectroscopy and accelerated exposure testing. This result is important, as it shows that hybrid sol–gel materials can be used in applications where protecting a metal or ally substrate is paramount, especially in thermally volatile environments.