Hybrid organic–inorganic sol–gel coatings with interpenetrating network for corrosion protection of tinplate

Novel hybrid organic–inorganic coatings with interpenetrating network were synthesized by the acid-catalyzed hydrolytic co-polycondensation of tetraethoxysilane and 3-metacryloxypropyltrimethoxysilane, followed by radical polymerization with methyl methacrylate and triallyl isocyanurate (TAIC). The hybrid coatings were characterized by Fourier transformed infrared spectroscopy, thermogravimetric analysis and scanning electron microscope, and their anti-corrosion behaviors were evaluated by potentiodynamic polarization, electrochemical impedance spectroscopy and salt spray test. The results indicated that the hybrid coatings exhibited excellent anti-corrosion ability by forming a physical barrier between metal and its external environment. Thermal stability of the hybrid coatings was increased after the addition of TAIC. Furthermore, hydrophobic properties of the hybrid coatings were examined by measuring the contact angles, and the change in wetting characteristics of the hybrid coatings was not obvious.     

Sol–gel derived hybrid coatings as an environment friendly surface treatment for corrosion protection of metals and their alloys

Sol?Cgel derived organic inorganic hybrid coatings are effective corrosion protective systems for metals. They offer an excellent adhesion to metal as well as to the subsequent coat via strong covalent bond and a three dimensional network of ?CSi?CO?CSi?C linkages which helps to retard the penetration of corrosive medium through the coating. Unlike conventional surface protection methodology, silane based pre-treatment is an environment friendly technology with number of advantages like room temperature synthesis, chemical inertness, high oxidation and abrasion resistance, excellent thermal stability, very low health hazard etc. Further, the hybrid silane provides required flexibility and an increased compatibility with the subsequent coating in multicoat systems. The performance properties of hybrid systems depend on number of parameters like type of silane (mono or bis), degree of hydrolysis, type and dosage of inhibitive/barrier pigments (in case of pigmented system), application techniques, curing temperature and curing schedule, need to be optimized. A guideline formulation for maximum corrosion resistance with low environmental impact consist of a superprimer (a bis-silane with conventional resins, chrome free inhibitive pigments and additives) followed by epoxy or polyurethane top coat as per the exposure conditions.     

Hybrid sol–gel based coatings for the protection of historical window glass

Medieval glass is commonly attacked by atmospheric pollutants conveyed by water, triggering the corrosion process. Current conservation strategies aim to maintain window glass in its original context, and so it is necessary to protect it from further degradation. Sol–gel technology is very effective for the preparation of protective films, using Si-alkoxide precursors chemically similar to the substrate. The present work discusses water-repellent hybrid sol–gel coatings made from tetra-ethyl-ortho-silicate with different quantities of Si-alkoxides, functionalized with various alkyl groups. The coatings were deposited using the dip-coating technique and characterized by UV–VIS and FT-IR spectroscopy. Static and dynamic contact angle measurements showed an overall homogeneity of the coatings and indicated improved water-repellency when functionalized by long alkyl chains. The coatings with best performance in terms of transparency and contact angle, and with the lowest organic content, were selected and applied to medieval-like glass samples. Colorimetric characterization was carried out using a spectrophotometric scanner before and after application of the coatings and no significant color changes were found. The electron microscopy images revealed relatively even, crack-free coatings, especially with higher organic contents. Contact angle and colorimetric measurements were repeated after accelerated ageing by exposure to UV light and an SO₂-saturated atmosphere. A significant decrease in the contact angle was observed only for the samples treated at the highest SO₂ concentration. The silica-based materials did not give reaction by-products, were water-repellent, compatible with the substrate, colorless, transparent, and stable under exposure to chemicals and light, thereby satisfying the main requirements for the conservation of Cultural Heritage.     

Organic–inorganic hybrid sol–gel pretreatments for corrosion protection of mild steel in neutral and acidic solutions

Research on Chemical Intermediates - This work aims to develop and study sol–gel-derived anticorrosion films for mild steel. Epoxy bis-silane precursor has been prepared by reaction of liquid...     

The influence of the inhibitor particle sizes to the corrosion properties of hybrid sol–gel coatings

The influence of the inhibitor particle size (nano and micro cerium dioxide) embedded in several hybrid sol–gel coating systems for the corrosion protection of aluminium AA2024 alloy was studied, as well as the influence of other parameters like the inhibitor loading level and the method of reticulation. The properties of the obtained coatings were evaluated by means of transmission electron microscopy, accelerated salt spray test and electrochemical impedance spectroscopy. All the varied parameters proved to have an important influence on the corrosion mechanism, and an improvement induced by the use of nanometric inhibitors in comparison with the micrometric ones was demonstrated. In the case of the strong reticulated matrix, an inhomogeneous dispersion of the inhibiting species (micro inhibitor) favours the tension formation, making the coating more vulnerable to the corrosion attack. For the same doping level it was observed that the reticulation with 1-methylimidazole (MI) leads to a slightly better corrosion protection. Concomitantly, it was shown that high loadings with inhibitors have an adverse effect on the corrosion protection.     

Anti-corrosion performance of aniline trimer-containing sol–gel hybrid coatings for mild steel substrate

Journal of Sol-Gel Science and Technology - Novel electroactive sol–gel hybrid coatings were synthesized by hydrolysis and condensation reaction of tetraethoxysilane (TEOS) and different mass...     

Influence of organic corrosion inhibitors on the corrosion performance of organic–inorganic hybrid coatings applied on aluminium alloy

The proposed work aims to develop and study sol–gel derived anticorrosion films for aluminium. To further improve performance of these films, organic corrosion inhibitors were incorporated into the films. The organic–inorganic hybrid films with and without corrosion inhibitors were deposited on an aluminium substrate by dip coating. The films were characterized by electrochemical impedance spectroscopy (EIS), DC polarisation techniques, and neutral salt spray test to evaluate their anticorrosion properties. This study shows that very low and very high MBT concentrations deteriorate the corrosion performance of coatings, and consequently, there is an optimum concentration of MBT. EIS results revealed a higher corrosion inhibitive activity of 2-mercaptobenzothiazole (MBT) compared to that of 2-amino-5-methylthiazole and 1,2,3 benzotriazole.     

Advanced sol–gel coatings for practical applications

One of the features of the sol–gel techniques is closeness to the industrial applications. Another feature is the variation of shapes of obtained materials like bulk, fiber, coating film, powder and so on. Among them, the author has focused on research of the sol–gel coatings on various substrates for practical applications as well as the fundamental research under the collaboration with industry. In this review, results of such research will be presented. These include (a) protective coating on metal sheets, (b) micropatterning on glass substrates, (c) water-repellant coating on windshields, (d) colored coating on glass bottles for easy recycling, (e) superhydrophobic and superhydrophilic coating on glass plates, and (f) anti-reflective coating on glass lenses for cameras. Some were highly successful, and some were not, of course. The author also contributed to the foundation of The Japanese Sol–Gel Society in 2003. The activities of The Society in these 8 years are introduced.     

Quinine doped hybrid sol–gel coatings for wave guiding and optical applications

Pure and quinine doped silica coatings have been prepared over sodalime glasses. The coatings were consolidated at low temperature (range 60–180 °C) preserving optical activity of quinine molecule. We designed a device to test the guiding properties of the coatings. We confirmed with this device that light injected in pure silica coatings is guided over distances of meters while quinine presence induces isotropic photoluminescence. With the combined use of both type of coatings, it is possible to design light guiding devices and illuminate regions in glass elements without electronic circuits.     

Study of corrosion protection of mild steel by eco-friendly silane sol–gel coating

The effects of dipping duration in the silane solution and the sol pH on the protective performance of an eco-friendly silane sol–gel coating consisting a mixture of tetraethoxysilane, methyltriethoxysilane and glycidyloxypropyltrimethoxysilane applied on mild steel substrate were studied in this paper using electrochemical techniques and surface analysis. In consistency with the data obtained from electrochemical impedance spectroscopy and polarization curves, electrochemical current noise fluctuation analysis, appearance of the power spectral density plots and noise resistance indicated the most efficient sol pH and immersion time in the silane solution. In this regard, field emission type scanning electron microscopy images and water contact angle values revealed impact of the sol pH on the film structure. The enhancement in protective performance of the hybrid coating resulting from optimum immersion in the silane solution with appropriate pH was connected to the film homogeneity and higher cross linking and thickness as well. Moreover, a good trend correlation was observed between the noise resistance and low-frequency impedance modulus data.     

The stability of sol–gel silica coatings in vacuum with organic contaminants

Sol–gel SiO₂ antireflective coatings were prepared with different post-treatments, and their performance in a vacuum environment with intentionally induced organic contaminants were studied in detail. The pores of the silica coating can be filled with contaminants, which can increase the refractive index of the film and also absorb or scatter the light and therefore reduce the transmittance. Heat treatment at low temperature can insure against the possible volatilization of the components of the coating, but does not prevent the adsorption of organic contaminants and the degeneration of the transmittance. If an ammonia and hexamethyldisilazane (HMDS) vapor treatment is adopted before heat treatment, the optical stability can be greatly enhanced by reducing the adsorption of contaminants. The increased resistance to contamination is due to changes in the coating’s structure and composition, including a reduction of the specific surface area and surface polarity as a result of ammonia treatment and HMDS treatment, respectively.     

Synthesis and characterization of sol–gel derived CNSL based hybrid anti-corrosive coatings

Thermally cured cashew nut shell liquid based hybrid coatings have been successfully developed using three step processes of malenization, silane modification and subsequent hydrolysis and condensation with tetra ethyl orthosilicate for corrosion protection of mild steel. The synthesized precursor was then characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy (¹H-NMR, ¹³C-NMR and ²⁹Si-NMR) for structural elucidation. Four different coating formulations were developed on the basis of silane content (5, 10, 15 and 20 %) in the coating and cured with hexabutoxymethylmelamine at 120 °C for 1 h. The completely cured coatings were evaluated for mechanical properties, solvent resistance, chemical resistance, hydrolytic stability and accelerated weathering properties. Scanning electron microscope/energy dispersive spectroscopy was used to analyse the morphological behaviour and elemental distribution of the coating. Results revealed that 20 % silane modification showed better overall properties as compared to other formulations due to formation of more metal–oxygen–silicon covalent bond at metal-coating interface.     

Ionic liquid-mediated sol–gel coatings for capillary microextraction

Ionic liquid (IL)-mediated sol–gel hybrid organic–inorganic materials present enormous potential for effective use in analytical microextraction. This opportunity, however, has not yet been explored. One obstacle to materializing this prospect arises from high viscosity of ILs significantly slowing down sol–gel reactions. In this work, we developed a method that overcomes this hurdle and provides IL-mediated advanced sol–gel materials for capillary microextraction (CME). We examined two different ILs: (a) a phosphonium-based IL, trihexyltetradecylphosphonium tetrafluoroborate, and (b) a pyridinium-based ionic liquid, N-butyl-4-methylpyridinium tetrafluoroborate. These ILs were evaluated in conjunction with two types of hydroxy-terminated polymers: (a) two Si–OH terminated polymers (PDMS and BMPO), and (b) two C–OH terminated polymers (PEG and polyTHF) that differ in their sol–gel reactivity. Scanning electron microscopy results demonstrate that ILs can serve as porogenic agents in sol–gel reactions. The IL-mediated sol–gel coatings prepared with silanol-terminated polymers provided up to 28 times higher extractions in off-line CME-GC compared to analogous sol–gel coatings prepared without any IL in the sol solution. Contrary to this, the IL-mediated sol–gel coatings prepared with C–OH terminated polymers provided lower extraction efficiencies compared to their IL-free counterparts. These observations were explained by (a) lower sol–gel reactivity of C–OH groups in PEG and polyTHF compared to Si–OH groups in PDMS and in hydrolyzed alkoxysilane precursors and (b) extremely high viscosity of ionic liquids. This study shows that IL-generated porous morphology alone is not enough to provide effective extraction media: careful choice of the organic polymer and the precursor with close sol–gel reactivity must be made to ensure effective chemical bonding of the organic polymer to the created sol–gel material to be able to provide the desired sorbent characteristics. Additionally, IL-mediated sol–gel PDMS coatings provided run-to-run RSD values of 4.2–5.0% and detection limits ranging from 3.2 ng/L to 17.4 ng/L. PDMS sol–gels prepared without ILs provided RSD values of 2.8–14.1%, and detection limits ranging from 4.9 ng/L to 487.0 ng/L.     

Preparation of photocurable silica–titania hybrid coatings by an anhydrous sol–gel process

Photocurable silica-titania hybrid coatings were prepared through an anhydrous sol–gel process. Moreover, test samples were prepared by the addition of definite ratios of fluoro acrylate oligomers into the formulations to manage the optical properties of transmitted light. Formulations were applied to corona-treated polycarbonate substrates. Upon adding the inorganic component to the coating material, thermal, mechanical, and other properties, such as hardness, gloss, contact angle, and flame resistance were improved. The photocured hybrid films showed an increase in the refractive index with increasing the titanium tetraisopropoxide content. As expected, a decrease was observed in the refractive index of the coatings with the incorporation of fluoro acrylate resin. The surface morphology of the hybrid films was characterized by ESEM analysis. In addition the chemical composition of the surface of the coatings was identified by ESEM–EDS technique. ESEM studies indicated that inorganic particles were dispersed homogenously throughout the organic matrix.     

Photostability and retention of UV absorber molecules in sol–gel hybrid UV-protective coatings

Highly efficient UV-protecting coatings were prepared, consisting on UV absorber molecules embedded in transparent sol–gel phenyl-functionalized silica thin-films. The photostability and retention of the molecules in the films depend strongly on parameters such as the composition of the hybrid host matrix, the UV-absorber loading in the matrix and the sol–gel preparation conditions. The amount of the modifying phenyl group was found to affect strongly the retention of the UV absorber molecules in the matrix. The retention of the molecules incorporated in the thin-films showed an increase of 21 times as the amount of the phenyl groups is reduced by a factor of 4. On the other hand, the incorporation of increasing amounts of Ph groups lead to a slight decrease of the photostability of the UV absorber molecules. The ability to control the parameters affecting the durability of the UV absorber molecules in the sol–gel matrices allows us increase the effectiveness of the UV-protective films and hence their potential usage in both, indoors and outdoors applications.     

A review of contamination-resistant antireflective sol–gel coatings

Sol–gel derived silica antireflective (AR) coatings have been widely used as the optical components for high peak power laser systems because of their excellent optical properties and high laser-induced damage thresholds. However, the sol–gel derived coatings have a high surface area that is more susceptible to be contaminated by absorption of trace amounts of water vapor and other volatile organic compounds from the environment. In this paper, the major approaches to fabricate contamination resistant sol–gel derived silica AR coatings have been extensively reviewed. Different approaches, including solution-phase and vapor-phase silanization, ammonia–water vapor treatment and fluorine modification have been discussed. The optical properties and laser-induced damage thresholds of modified coatings have also been evaluated. The improved sol–gel AR coatings have been shown to possess superior contamination resistance to work in vacuum systems compare to the traditional sol–gel AR coatings.     

Hybrid sol–gel coatings doped with transition metal ions for the protection of AA 2024-T3

The protective capabilities of sol–gel coatings are determined by their physical barrier properties. For an effective protection, a homogenous crack-free material is required, which prevents from attacks of corrosive species. When the coating is damaged, active corrosion protection is usually achieved by the use of inhibitors. Among the different inhibitors rare earth ions and especially cerium have shown effective inhibiting properties. Due to the complexity of the corrosion processes, a combination of inhibitors is expected to be superior to a monocomponent inhibiting. The aim of this study was to prove which other ions, used in combination with cerium, can improve the corrosion protection abilities of hybrid silica based inorganic–organic sol–gel coatings applied on aluminium alloy 2024 substrates. Mixtures of cerium nitrate with two other potential inhibitor substances were incorporated into a sol–gel matrix and their behaviour in neutral salt spray test and during EIS measurements was investigated. The Ce–P–Pr inhibitor combination (Ce³⁺, PO₄ ³⁻, Pr³⁺) has shown the best long-term corrosion protection properties at low doping levels.     

Antimicrobial coatings on textiles–modification of sol–gel layers with organic and inorganic biocides

Antimicrobial textile materials were produced by sol–gel coatings with embedded biocidal compounds. For preparation a sol–gel procedure was used, starting from pure silica sols and 3-glycidyloxypropyltriethoxysilane (GLYEO) containing silica sols. These sols were modified with silver compounds, hexadecyltrimethyl-ammonium-p-toluolsulfonat (HTAT) and copper compounds, respectively. The investigations were performed on viscose fabrics as function of the concentration of biocidal compounds and of thermal treatment of textile after dip-coating between 80 up to 180 °C. The use of modified silica coatings leads to a decreased growth of fungi (Aspergillus niger) and bacteria (Bacillus subtilis and Pseudomonas putida) with increasing amount of the biocide embedded in the coating. The addition of GLYEO supports the biocidal effect of the coatings and enhances the stability of the coating solutions. For preparation of antimicrobial silica coatings the biocides silver, copper or HTAT can be used alone but the combination of these compounds leads to enhanced results against both fungi and bacteria. Therefore silica sols containing a combination of different types of biocides may be used for antimicrobial modification of textiles in some practical applications. For industrial applications the here presented coating solutions are especially advantageous, because of 90% water content in the solvent.