Self-healing Coatings For Corrosion Protection Research Articles

Hybrid Ceramic Self-Healing Coatings for Corrosion Protection of Al Alloys in 3% NaCl Solution

This work focuses on the development of sol–gel self-healing coatings for corrosion protection of Al alloys. The use of this method will help to reduce the costs associated with the coating as well as their environmental impact. Coatings were made of a titania matrix loaded with microparticles of poly(vinyl-alcohol) (PVA) containing cerium nitrate as an inhibitor. The PVA particles dissolve in water, so that the cerium nitrate deposits on the Al surface subjected to corrosion. The PVA microspheres were made via the emulsion method, and then loaded with cerium nitrate. The amount of cerium nitrate loaded in the microspheres was evaluated using UV–Vis. As a second step, the titania coating with embedded PVA microspheres loaded with cerium nitrate was deposited on an AA6082 substrate via a sol–gel route. The corrosion resistance of the coated samples was tested in NaCl solution. The coating microstructure, before and after the corrosion tests, was analysed with the use of an SEM (scanning electron microscope) and EDS (energy dispersive spectroscopy), while the corrosion resistance was investigated by EIS (electrochemical impedance spectroscopy). The results showed that the coatings were uniform and compact. They also showed the ability of the hybrid TiO2-based coating to provide protection for the AA6082 from corrosion. The coatings with an induced defect (scratch) were also analysed, and the EIS analysis of the coatings over time showed an increase in resistance, confirming the ability of the coating to heal itself.

Corrosion-Responsive Self-Healing Coatings.

Organic coatings are one of the most popular and powerful strategies for protecting metals against corrosion. They can be applied in different ways, such as by dipping, spraying, electrophoresis, casting, painting, or flow coating. They offer great flexibility of material designs and cost effectiveness. Moreover, self-healing has evolved as a new research topic for protective organic coatings in the last two decades. Responsive materials play a crucial role in this new research field. However, for targeting the development of high-performance self-healing coatings for corrosion protection, it is not sufficient just to focus on smart responsive materials and suitable active agents for self-healing. A better understanding of how coatings can react on different stimuli induced by corrosion, how these stimuli can spread in the coating, and how the released agents can reach the corroding defect is also of high importance. Such knowledge would allow thedesign of coatings that are optimized for specific applications. Herein, the requirements and possibilities from the corrosion and synthesis perspectives for designing materials for preparing self-healing coatings for corrosion protection are discussed.

Self-Healing Coatings for Corrosion Protection: The Importance of the Transport of Active Agents from the Coating Towards the Defect

In so called smart or intelligent self-healing coatings active agents that are safely stored inside the coating are released upon onset of corrosion. This release is triggered by a suitable trigger signal that should be a safe indicator for the onset of corrosion and its continuation. Different from the current standard where release from pigments occurs via leaching, the safe storage should ensure that there is no uncontrolled release of the active agents when they are not needed for inhibiting corrosion and restoring protection. While there are many studies on different concepts for storage and active release triggered by corrosion, achieving an efficient transport of the released agents to the defective site(s) is a likewise crucial but so far widely neglected issue. Recently it was proposed that the signal spreading from the defect into the coating can be significantly enhanced by the use of layers of conducting polymer, such as polypyrrole, applied as an intermediate layer between the metal substrate and the organic coating. In that case the decrease in potential is the signal that is spread. Here, we will show that by such polypyrrole layers also the transport of active agents can be significantly enhanced. To enable a fundamental in-depth study of the mobility of active agents from the coating towards the defective site, a dedicated experimental model set-up was designed especially for the study of ions transport. The main question to be addressed was whether the main transport will be along the metal│PPy interface or rather through the matrix of the reduced polypyrrole. Zinc was chosen as metallic substrate, owing to its importance in galvanized steel products. The corrosion potential at the defective site was used as a measure for the amount of corrosion inhibitor released into the defect and hence as a measure to reflect the ionic transport and self-healing efficiency of the coating by different corrosion inhibitors. The progress of polypyrrole reduction, in turn, was monitored by use of Scanning Kelvin Probe (SKP) for recording the change of potential as a function of distance from the defect and of time. The concentration of corrosion inhibitor at the defective site was also quantified using ICP-MS (OES) analysis of the solution in the defect at different times. In order to ensure for reliable quantification of the transport that released corrosion inhibitor moving towards the defect is not reacting with corroding metal at the interface special PVB│PPy│Au-Glass model samples were utilized. The results indicate that Ce4+ is more effective than Ce3+ for reaching and passivating the defect. In addition, organic corrosion inhibitors (8-HQ, β-CD and L-Car) were found to be highly efficient in inhibiting the defective site. This is proposed to be due through a synergistic mechanism, which is based on an interaction of the passivating effect of these corrosion inhibitors and the passivating effect of polypyrrole. The synergistic mechanism shows astonishing passivation effects, resulting in anodic potential shifts of the corrosion potential of more than 600 mV. Concerning the main path for ionic transport, it was found that this occurs mainly through the matrix of the (partially) reduced polypyrrole. Hence, the transport of positive ions should be favored compared to the one of negative ions.

Effective release of corrosion inhibitor by cellulose nanofibers and zeolite particles in self-healing coatings for corrosion protection

Self-healing polymer coatings made up of different concentrations of cellulose nanofibers and zeolite particles were investigated for the ability to effectively release corrosion inhibitor. The electrochemical impedances of scratched specimens were monitored in a corrosive solution. The release behavior of corrosion inhibitor was measured via mass changes in a polymer sheet. Coatings containing both cellulose nanofibers and zeolite particles led to large and sustained releases of corrosion inhibitor. Increases in the zeolite particles connected to cellulose nanofibers increased the pH, which led to a two-step release of corrosion inhibitor that was aided by the nanofibers that served as pathways.

Smart Coatings for Corrosion Protection: On the Need for New Coating Concepts

Ideally smart coatings for corrosion protection have to be able to protect the underlying metal from corrosion by providing excellent barrier properties, at the same time showing a fast and efficient self-healing in case a defect down to the metal is inflicted into them, while being as delamination resistant as possible.These seem to be basically incompatible properties, as either mobility of species is high or the coating is highly impermeable, i.e. it is difficult to envisage a coating that can be both at the same time. In fact, in recent works we have shown that for excellent self-healing performance especially the resistance against cathodic delamination of a coating should be significantly weakened [1, 2]. Using conductive polymer additions to non-conductive coatings, both high self-healing activity [1-3] as well as high resistance against cathodic delamination [4, 5] can be controlled in a wide range.Based on an in-depth understanding of the underlying mechanisms we are currently working on strategies for developing coatings that show excellent active as well as passive protection properties. Latest progress of the research on this topic well be presented and the implication will be discussed.[1] M. Uebel, L. Exbrayat, M. rabe, T.H. Tran, D. Crespy, M. Rohwerder, On the Role of Trigger Signal Spreading Velocity for Efficient Self-Healing Coatings for Corrosion Protection, Electrochem. Soc. 165 (2018) C1017-C1027[2] H. Tran , A. Vimalanandan , G.Genchev , J. Fickert , K. Landfester, D. Crespy , M.Rohwerder, Regenerative Nano-Hybrid Coating Tailored for Autonomous Corrosion Protection, Advanced Materials 27(25) (2015) 3825-3830[3] A. Vimalanandan, L.P. Lv, T.H. Tran, K. Landfester, D. Crespy, M. Rohwerder, Redox-Responsive Self-Healing for Corrosion Protection, Advanced Materials 25(48) (2013) 6980-6984[4] Anna Merz, Matthias Uebel, Michael Rohwerder, The Protection Zone: A Long-Range Corrosion Protection Mechanism around Conducting Polymer Particles in Composite Coatings: Part I. Polyaniline and Polypyrrole, Electrochem. Soc. 166 (2019) C304-C313[5] Anna Merz, Michael Rohwerder, The Protection Zone: A Long-Range Corrosion Protection Mechanism around Conducting Polymer Particles in Composite Coatings: Part II. PEDOT:PSS, Electrochem. Soc. 166 (2019) C314-C320

A review on self-healing coatings for corrosion protection of metals

A review on self-healing coatings for corrosion protection of metals

Aluminum pillared montmorillonite clay-based self-healing coatings for corrosion protection of magnesium alloy AZ91D

In the present study, aluminum pillared montmorillonite clay was modified with cationic corrosion inhibitors Ce3+/Zr4+. The modification of the montmorillonite clay was carried out by two methods; (a) by simple mixing of inhibitor solutions along with clay by stirring for 30 min and (b) by homogenization of inhibitor solutions and clay for a very short time of 15 min followed by evacuation. The modified and as-received clays were dispersed in hybrid organic-inorganic sol-gel matrix silica sol, which were coated on magnesium alloy AZ91D and cured in air at 130 °C for 1 h. Corrosion protection ability of coatings was evaluated by electrochemical impedance spectroscopy, potentiodynamic polarization and weight loss measurements after exposure to 3.5 wt% NaCl solution for different exposure durations between 24 h to 120 h. Coatings were evaluated for their self-healing ability using scanning vibrating electrode technique for varying time duration from 1 h to 24 h. Coatings generated with the sol using the pillared montmorillonite clay after modification as described in (b) were found to exhibit better anticorrosive properties even after prolonged exposure to the corrosive medium.

On the Role of Trigger Signal Spreading Velocity for Efficient Self-Healing Coatings for Corrosion Protection

Smart self-healing coatings for corrosion protection safely store active substances which are only released when corrosion occurs. This type of case-sensitive release has to be triggered by parameters that change as a consequence of corrosion. Examples are a change of pH, ionic strength, and electrochemical potential. In most technically relevant applications, a global release of active substances is not possible, i.e. the spreading of the signal which triggers the release of active substances is restricted to a lateral transport through the coating. Hence, the ability of the trigger signal to spread quickly through the coating from the local corroding area is crucial to create highly responsive and effective self–healing coatings. Here we show how the velocity at which the trigger signal spreads laterally along the metal|coating interface can be accelerated and how a penetration of the signal vertically into the coating, i.e. far away from the metal|coating interface, can be achieved.

Advanced microcapsules for self-healing conversion coating on magnesium alloy in Ce(NO3)3 solution with microcapsules containing La(NO3)3

Microcapsules with self-healing coatings for corrosion protection of magnesium substrates have attracted tremendous interest due to their capability of preventing the propagation of cracks in protective coatings by releasing inhibitors from the microcapsules. Gelatin-chitosan microcapsules containing La(NO3)3 were prepared by complex coacervation. The morphology of the cerium-based conversion coating shows a globular structure with microcapsules distributing in the tiny cracks of the coating. In 3.5 wt% sodium chloride solution environment, the coating is damaged and microcapsules migrate into the damaged area, the triggering release of inhibitors supplement to the conversion coating. The cerium conversion coating with microcapsules shows a much higher corrosive resistance than the coating without microcapsules, and demonstrates the achievement of a self-healing performance.

Development of self-healing coatings for corrosion protection on metallic structures

Inspired by biological systems, artificial self-healing materials are designed for repairing local damage caused by external factors. The rapidly expanding field of self-healing systems contains, among others, materials with well-defined surface properties. Undoubtedly, enhancing surface functionalisation, by applying smart coatings, enjoys an extensive interest. The self-healing ability is particularly essential property for corrosion protection strategies, especially when the use of one of the most effective corrosion systems, based on chromium(VI) compounds, is now banned by the current registration, evaluation, authorisation and restriction of chemicals legislation. Self-healing protective coatings are produced using macromolecular compounds, ceramics, metals and composites. Considering the wide range of available materials, the number of potential combinations seems to be unlimited. The self-healing action of such coatings is activated by appropriate stimuli: temperature changes, radiation, pH changes, pressure changes and mechanical action. In this paper, the research and practical implications of the various approaches to achieving self-healing functionality of protective coatings, as well as potential developments in this area, are explored.

Shape memory composite (SMC) self-healing coatings for corrosion protection

Abstract A shape memory composite (SMC) coating with a self-healing ability was prepared by a facile method based on a thermoresponsive shape memory polymer (SMP) that utilized carnauba wax microparticles as the healing agent. Damages to the SMC coating was healed via heating, which triggered a two-step healing mechanism consisting of defect closure through a shape memory effect at 65 °C and then defect sealing by molten wax at 90 °C. The surface morphologies of the scratched and healed coatings as well as a wax-free SMP coating were first studied by optical stereomicroscopy and scanning electron microscopy (SEM). To assess the recovery of the coating’s barrier properties, macroscopic and localized information was obtained by electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM), respectively. The healing performance was also evaluated by comparing the macroscopic morphologies of the intact, damaged and healed coatings after long-term immersion. The results from both tests were in agreement and confirmed the key roles of carnauba wax microparticles in the complete recovery of the barrier properties of initially damaged coatings upon thermally assisted self-healing.

自己修復性防食コーティング

自己修復性防食コーティング