Coatings tailored to corrosion protection of metallic substrates are of the utmost relevance to ensure reliability and long-term performance of coated parts as well as the product value of the coated ...materials. Presently, there is a strong emphasis on the development of advanced functional and smart coatings for corrosion protection in different technological applications. On the one hand, there is a need for more advanced coatings for conventional applications and, on the other hand, there is a need to answer the requirements of several new Hi-Tech applications. Thus, this review highlights the most recent trends in the field of functional coatings for corrosion protection of metallic materials in a wide range of technical applications. Emphasis is given to self-healing coatings and smart coatings combining multiple functionalities for increased corrosion protection. Recent developments on the introduction of functionalities based on encapsulation of corrosion inhibitors, anti-fouling agents and superhydrophobic additives or modification of organic and hybrid matrices via chemical manipulation are reviewed. Special attention is dedicated to functional coatings for corrosion protection of bioresorbable metallic implants that have an important impact in biomedical applications.
•Smart and self healing coatings for corrosion protection•Hydrophobic and superhydrophobic coatings•Functional coatings based on modified polymeric and hybrid chemistries•Functional coatings for functionalisation and protection metallic biomaterials
Direct assembling of N-graphene, i.e. nitrogen doped graphene, in a controllable manner was achieved using microwave plasmas at atmospheric pressure conditions. The synthesis is accomplished via a ...single step using ethanol and ammonia as carbon and nitrogen precursors. Tailoring of the high-energy density plasma environment results in a selective synthesis of N-graphene (~0.4% doping level) in a narrow range of externally controlled operational conditions, i.e. precursor and background gas fluxes, plasma reactor design and microwave power. Applying infrared (IR) and ultraviolet (UV) irradiation to the flow of free-standing sheets in the post-plasma zone carries out changes in the percentage of sp
, the N doping type and the oxygen functionalities. X-ray photoelectron spectroscopy (XPS) revealed the relative extension of the graphene sheets π-system and the type of nitrogen chemical functions present in the lattice structure. Scanning Electron microscopy (SEM), Transmission Electron microscopy (TEM) and Raman spectroscopy were applied to determine morphological and structural characteristics of the sheets. Optical emission and FT-IR spectroscopy were applied for characterization of the high-energy density plasma environment and outlet gas stream. Electrochemical measurements were also performed to elucidate the electrochemical behavior of NG for supercapacitor applications.
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► CaCO3 microbeads were used as pH-sensitive reservoirs for corrosion inhibitors. ► The barrier properties of the coating with CaCO3/inhibitors were improved. ► The corrosion ...inhibitors were released as a result of dissolution of pH sensitive CaCO3. ► LEIS demonstrated the local corrosion inhibition provided by the CaCO3/Ce over localised defect formed in the coating.
Corrosion protection of aluminium alloys often relies on the application of a coating on the metallic surface. The coating normally combines a barrier effect that restricts the ingress of corrosive species, with an inhibitive role induced by corrosion inhibitor pigments added to the coating formulation. However, the direct addition of corrosion inhibitors to the coating can cause some detrimental interactions between components, as well as formation of preferential electrolyte pathways, compromising the barrier properties. Moreover, electrolyte uptake and ageing may result in leaching of those corrosion inhibitors. In order to extend the corrosion inhibition ability of organic coatings one possible solution is to store the inhibitors inside nano or microreservoirs compatible with the coating matrix and able to sense the local changes induced by the corrosion process. This strategy has led to the development of a new generation of “smart” coatings for anti-corrosion purposes. The aim of this work is to study the anti-corrosion properties of water-based epoxy coatings loaded with pH sensitive particles, acting as feedback active containers for corrosion inhibitors and applied on the aluminium alloy AA2024-T3. For this purpose micron size calcium carbonate beads were modified with different corrosion inhibitors: cerium nitrate, salicylaldoxime and 2,5-dimercapto-1,3,4-thiadiazolate. These particles act as pH sensitive reservoirs because they dissolve at acidic pH, releasing the corrosion inhibitor, which then suppresses the corrosion activity of the bare metal. Electrochemical impedance spectroscopy (EIS) was used to estimate the electrical parameters assigned to the barrier properties of the coating and corrosion inhibition ability in the presence of inhibitor loaded calcium carbonate beads. The most relevant corrosion inhibition effects were observed from CaCO3 microbeads modified with cerium ions. The self healing potential of this new system was corroborated by localised electrochemical impedance measurements (LEIS).
This work aims at studying the electrochemical behavior, by Electrochemical Impedance Spectroscopy (EIS), of austenitic (AISI 304 and AISI 316) and duplex (SAF 2205 and SAF 2304) stainless steels, ...when embedded in concrete specimens. Concrete specimens were exposed to chloride containing solutions simulating the aggressive conditions found in sweater environments. Samples were fully immersed and submitted to periodic immersion/emersion cycles. EIS and open circuit potential (OCP) were monitored in a monthly basis. Samples containing carbon steel (C-steel) rebars were also prepared for comparison of the corrosion rates between the different materials.
The results showed that the austenitic and duplex SAF 2205 stainless steels were passive for all the testing period, due to the formation of protective oxide layer, with the AISI 316 presenting the higher corrosion resistance value. The EIS results suggest an increase of more than one order of magnitude in the corrosion resistance of the duplex steels and AISI 316 comparatively to C-steel rebars.
The high corrosion rate of magnesium alloys is the main drawback to their widespread use, especially in biomedical applications. There is a need for developing new coatings that provide ...simultaneously corrosion resistance and enhanced biocompatibility. In this work, a composite coating containing polyether imide, with several diethylene triamine and hydroxyapatite contents, was applied on AZ31 magnesium alloys pre-treated with hydrofluoric acid by dip coating. The coated samples were immersed in Hank’s solution and the coating performance was studied by electrochemical impedance spectroscopy and scanning electron microscopy. In addition, the behavior of MG63 osteoblastic cells on coated samples was investigated. The results confirmed that the new coatings not only slow down the corrosion rate of AZ31 magnesium alloys in Hank’s solution, but also enhance the adhesion and proliferation of MG63 osteoblastic cells, especially when hydroxyapatite nanoparticles were introduced in the coating formulation.
► The passivation and passivation breakdown of AISI 304 in alkaline solutions with different pH was studied. ► The electrochemical behaviour and the corrosion resistance in chloride environments were ...evaluated using d.c. potentiodynamic polarization and electrochemical impedance spectroscopy. ► The results were modelled using a hierarchically distributed circuit and revealed a more susceptible surface at pH 9. ► The passive film characterization was carried out by SEM and EDS analysis, revealing the existence of MnS inclusions and the increase of Cr/Fe ratio in the attacked areas, preferably the vicinity of those inclusions.
Nowadays, stainless steel reinforcements appear as an effective solution to increase the durability of reinforced concrete structures exposed to very aggressive environments. AISI 304 is widely used for this purpose. Although the improved durability of reinforcing AISI 304, when compared to carbon steel, there is a high probability of pitting susceptibility in the presence of chlorides. Thus, the present work aims at studying the passivation and passivation breakdown of AISI 304 in alkaline solutions of different pH (pH from 13 to 9), simulating the interstitial concrete electrolyte. These solutions were contaminated with different concentrations of chloride ions (3% and 10%, as NaCl). The electrochemical behaviour was evaluated by d.c. potentiodynamic polarization and by electrochemical impedance spectroscopy (EIS).
The morphological features and the changes observed in the surface composition were evaluated by Scanning Electron Microscopy (SEM) together with EDS chemical analysis.
The results evidence that pH plays an important role in the evolution of the film resistance and charge transfer processes. Moreover, the effect is highly dependent upon the chloride content and immersion time.
Nowadays, there is a strong demand on the search of thinner, but more effective organic coatings for corrosion protection of metallic substrates, like galvanised steel, used in the automotive ...industry. In order to guarantee effective corrosion protection of these coatings, and because chromate-based pigments cannot be used, one of the most attractive strategies consists on the modification of the organic matrix with nano-additives filled with corrosion inhibitors, which can be released to the active sites. In this work, two different nano-additives are explored as potential self-healing materials for the development of active protective coatings. These additives are layered double hydroxides and cerium molybdate hollow nanospheres loaded with mercaptobenzothiazole, as a corrosion inhibitor. These additives were added to epoxy primers, individually, or combining the two nanoadditives in the same layer.
The electrochemical behaviour and the potential of self-healing ability were studied by electrochemical impedance spectroscopy, scanning vibrating electrode technique and scanning ion-selective electrode technique. The results reveal that both types of nanocontainers can provide effective corrosion inhibition on artificial induced defects, at different stages of the degradation process. Moreover, the results also show that there is a synergistic effect concerning corrosion inhibition and self-healing potential when a mixture of the two nanocontainers is used. The mechanism of self healing is presented and discussed in terms of effect of organic inhibitor and role of the nanocontainers, including effect of cerium ions released from cerium molibdate nanoparticles.
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•Novel cerium tri(bis(2-ethylhexyl)phosphate) corrosion inhibition additive.•High compatibility with epoxy coatings.•Increased corrosion resistance of coated steel panels.•Corrosion ...healing in defects.•Synergistic cathodic and anodic corrosion inhibitors.
In this work cerium tri(bis(2-ethylhexyl)phosphate) (Ce(DEHP)3) particles were used as anti-corrosion pigments in epoxy coatings applied on steel coupons. The composition of the corrosion inhibitor was designed to introduce pH-stimulated corrosion healing in the coating. Electrochemical Impedance measurements demonstrated very high compatibility between the inhibitor and the coating, and effective and stable corrosion protection. Localized electrochemical measurements carried out using the Scanning Vibrating Electrode Technique and Localised Electrochemical Impedance revealed efficient corrosion inhibition of steel exposed in artificially damaged coatings.
This work aims to develop and study new anticorrosion films for AZ31B magnesium alloy based on the sol–gel coating approach.
Hybrid organic–inorganic sols were synthesized by copolymerization of ...epoxy-siloxane and titanium or zirconium alkoxides. Tris(trimethylsilyl) phosphate was also used as additive to confer additional corrosion protection to magnesium-based alloy. A sol–gel coating, about 5-μm thick, shows good adhesion to the metal substrate and prevents corrosion attack in 0.005
M NaCl solution for 2 weeks. The sol–gel coating system doped with tris(trimethylsilyl)-phosphate revealed improved corrosion protection of the magnesium alloy due to formation of hydrolytically stable Mg–O–P chemical bonds.
The structure and the thickness of the sol–gel film were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The corrosion behaviour of AZ31B substrates pre-treated with the sol–gel derived hybrid coatings was tested by electrochemical impedance spectroscopy (EIS). The chemical composition of the silylphosphate-containing sol–gel film at different depths was investigated by X-ray photoelectron spectroscopy (XPS) with depth profiling.
This work investigates the protective behaviour of bis-triethoxysilylpropyl tetrasulfide silane pre-treatments on the AZ31 Mg alloy. The silane solution was modified by the addition of cerium nitrate ...or lanthanum nitrate in order to introduce corrosion inhibition properties in the silane film.
The corrosion behaviour of the pre-treated AZ31 magnesium alloy was studied during immersion in 0.005
M NaCl solution, using electrochemical impedance spectroscopy and the scanning vibrating electrode technique (SVET). The electrochemical experiments showed that the presence of cerium ions or lanthanum ions improve the protective behaviour of the silane film. The SVET experiments evidenced that the presence cerium in the silane film led to an important reduction of the corrosion activity.
The results demonstrate that either cerium ions or lanthanum ions can be used as additives to the silane solutions to improve the performance of the pre-treatments for the AZ31 magnesium alloy.
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