Evaluation of self-healing properties of inhibitor loaded nanoclay-based anticorrosive coatings on magnesium alloy AZ91D (original) (raw)
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Chemistry of Materials, 2007
The development of active corrosion protection systems for metallic substrates is an issue of prime importance for many industrial applications. The present work shows a new contribution to the development of a new protective system with self-healing ability composed of hybrid sol-gel films doped with nanocontainers that release entrapped corrosion inhibitor in response to pH changes caused by corrosion process. A silica-zirconia based hybrid film was used in this work as an anticorrosion coating deposited on 2024 aluminum alloy. Silica nanoparticles covered layer-by-layer with polyelectrolyte layers and layers of inhibitor (benzotriazole) were randomly introduced into the hybrid films. The hybrid film with the nanocontainers reveals enhanced long-term corrosion protection in comparison with the undoped hybrid film. The scanning vibrating electrode technique also shows an effective self-healing ability of the defects. This effect is obtained due to regulated release of the corrosion inhibitor triggered by the corrosion processes started in the cavities. The approach described herein can be used in many applications where active corrosion protection of materials is required.
Environmentally friendly sol - gel-based anticorrosive coatings on aluminum alloy 2024
Materials Research, 2013
Chromate coatings used as corrosion protection technologies for aluminum alloys are environmentally harmful and extremely toxic. This paper presents an investigation on the deposition of environmentally friendly cerium oxide-based anticorrosive coatings on aluminum alloy 2024 substrates by the sol-gel method. The influence of the calcination temperature on both the microstructural characteristics and the electrochemical corrosion performance was tested using scanning electron microscopy, X-ray diffraction, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), before and after, periods of immersion in saline corrosive solutions. The ceramic coatings synthesized at 200, 300 and 400 °C showed very resistive behaviors leading to both an efficient passivation of the alloy surfaces and good corrosion protection. This passivation was maintained for 30 days of immersion in saline solutions, as well as, when aggressive electrochemical polarization experiments (until 2.0 V versus saturated calomel electrode) were used. Very high resistances for the charge transfer (0.14-0.28 GΩ) and very low current density values (5 × 10-14-5 × 10-11 A cm-2) were estimated by EIS and potentiodynamic polarization, respectively, for coatings prepared at 200-400 °C. Thus, the coatings prepared in this study by the sol-gel method appear as an efficient treatment for the corrosion protection of aluminum alloys.
Progress in Organic Coatings, 2019
Sol-gel coatings were prepared from mixing tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) and then applied on the pre-treated AZ91 magnesium alloy by using the dip coating technique. The formation and morphological characteristics of the coatings were analyzed by using Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). Three salts were incorporated into the coatings, and their corrosion inhibition performance was investigated by using electrochemical impedance spectroscopy (EIS) in 3.5% sodium chloride solution. The results indicate that the addition of sodium gluconate (NaC 6 H 11 O 7), potassium hypophosphite (KH 2 PO 2), and manganese (II) acetate (Mn(CH 3 CO 2) 2) as inhibitors with a concentration of 0.1, 0.5, and 0.1 wt%, respectively to the coatings can enhance corrosion resistance. It was also found that the inhibition performance of the salt-containing coatings is highly improved when 0.5 wt% of cloisite 20A nanoparticle as the surface modifier is added to the coating.
Journal of Nanoparticle Research, 2013
This study is focused on the fabrication, characterization, and application of corrosion protective coatings to magnesium alloy ZK30. Hybrid organic-inorganic coatings were synthesized using organic-modified silicates together with resins based on bisphenol A diglycidyl ether. Cerium molybdate nanocontainers (ncs) with diameter 100 ± 20 nm were loaded with corrosion inhibitor 2-mercaptobenzothiazole and incorporated into the coatings in order to improve their anticorrosion properties. The coatings were investigated for their anticorrosion and nanomechanical properties. The morphology of the coatings was examined by scanning electron microscopy. The composition was estimated by energy-dispersive X-ray analysis. The mechanical integrity of the coatings was studied through nanoindentation and nanoscratch techniques. Scanning probe microscope imaging of the coatings revealed that the addition of ncs creates surface incongruity; however, the hardness to modulus ratio revealed significant strengthening of the coating with increase of ncs. Studies on their corrosion behavior in 0.5 M sodium chloride solutions at room temperature were made using electrochemical impedance spectroscopy. Artificial defects were formatted on the surface of the films in order for possible self-healing effects to be evaluated. The results showed that the coated magnesium alloys exhibited only capacitive response after exposure to corrosive environment for 16 months. This behavior denotes that the coatings have enhanced barrier properties and act as an insulator. Finally, the scratched coatings revealed a partial recovery due to the increase of charge-transfer resistance as the immersion time elapsed.
Recent Development in Clay Based Functional Coating for Corrosion Protection
Key Engineering Materials
There is a large variety of techniques available to protect metals from various types of corrosion. Till date chromate containing metal coatings is one of the most commonly used methods. Layered clays are basically of two types depending on the type of ion exchange capacity. In the recent years different researchers demonstrated the use of such cation/ anionic clays as potential nanocontainers for the inhibitors. These nanocontainers can be used in the coating to induce self-repairing capacity when the coating surface is damaged. Due to the disturbance in the pH and availability of chloride ions clay based nanocontainers can release the inhibitor to protect the surface. In the recent year use of anionic clay like hydrotalcites or layered double hydroxides are much studied in comparison to cationic clay like montmorillonite. This review critically analysed the potential of these clay in the future development of self-healing coating.
Hybrid sol-gel coatings doped with cerium to protect magnesium alloys from corrosion
Materiali in Tehnologije
Hybrid coatings produced via the sol-gel route were deposited onto an Elektron 21 magnesium alloy. The sol consisted of tetraethyl-orthosilicate (TEOS) and 3-(trimethoxysilyl)propylmethacrylate (MAP) to which corrosion inhibitors were added. The influence of the cerium concentration on the anti-corrosion properties of the hybrid coating is presented. Furthermore, the morphology of the organic/inorganic coatings deposited on the magnesium alloy was determined with scanning electron microscopy (SEM). In parallel, the electrochemical behavior during the immersion in a 0.05 M NaCl corrosive solution was studied with electrochemical impedance spectroscopy (EIS). It was proven that the hybrid films exhibit a high impedance modulus during the first hours of the immersion and that an addition of cerium to the sol with a concentration of 0.01 M considerably increases the durability of the film, delaying its degradation during the immersion. In addition, this project especially focusses on determining the critical concentration of the cerium salt at which the impedance modulus of the hybrid coating strongly decreases during the immersion.
Evaluation of Corrosion Protection of Sol-Gel Coatings on AZ31B Magnesium Alloy
2008
Magnesium is one of the lightest metals and magnesium alloys have good strength to weight ratio making them very attractive for many particular applications [1]. The main drawback of magnesium alloys is their high corrosion susceptibility. Improving the corrosion protection by deposition of thin hybrid films can expand the areas of applications of relatively cheap magnesium alloys. This work aims at investigation of new anticorrosion coating systems for magnesium alloy AZ31B using hybrid sol-gel films. The sol-gels were prepared by copolymerization of 3glycidoxypropyltrimethoxysilane (GPTMS), titanium alcoxides and special additives which provide corrosion protection of magnesium alloy. Different compositions of sol-gel systems show enhanced long-term corrosion protection of magnesium alloy. The sol-gel coatings exhibit excellent adhesion to the substrate and protect against the corrosion attack. Corrosion behavior of AZ31B substrates pre-treated with sol-gel derived hybrid coatings was tested by Electrochemical Impedance Spectroscopy (EIS). The morphology and the structure of sol-gel films under study were characterized with SEM/EDS techniques.
Inhibitor-doped sol–gel coatings for corrosion protection of magnesium alloy AZ31
Surface and Coatings Technology, 2010
This work presents new anticorrosive coatings for the AZ31 magnesium alloy, based on hybrid sol-gel films doped with a corrosion inhibitor. The sol-gel coatings were prepared by copolymerization of 3glycidoxypropyltrimethoxysilane and zirconium (IV) tetrapropoxide. 8-Hydroxyquinoline (8-HQ) was chosen as a corrosion inhibitor to be incorporated into the sol-gel films at two different stages of synthesis, either before or after hydrolysis of the sol-gel precursors. The effectiveness of 8-HQ for corrosion suppression on AZ31 was verified by Scanning Vibrating Electrode Technique. Electrochemical Impedance Spectroscopy was used to monitor the evolution of the substrate/film systems in the course of immersion in 0.005 M NaCl. The morphology and the structure of the sol-gel films were characterized with SEM/EDS and TEM techniques. The sol-gel films exhibit good adhesion to the metal substrate and prevent the corrosive attack during 2 weeks under immersion test. Results showed that addition of inhibitor into the sol-gel films enhances the corrosion protection of the magnesium alloy and does not lead to deterioration of the barrier properties of the sol-gel matrix.
Sol–gel coatings on metals for corrosion protection
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 and had showed the potential for the replacement of toxic pretreatments and coatings which have traditionally been used for increasing corrosion resistance of metals. This review covers the recent developments and applications of sol-gel protective coatings on different metal substrates, such as steel, aluminum, copper, magnesium and their alloys. The challenges for industrial productions and future research on sol-gel corrosion protective coatings are also briefly discussed.