A mussel-inspired delivery system for enhancing self-healing property of epoxy coatings

Dopamine (DA),one type of mussel-inspired biological molecules with adhesive nature and corrosion inhibitor property,are often used to functionalize the surfaces of various materials.Herein,we report the application of polydopamine (PDA) microcapsules as novel nanocontainers for the purpose,loading corrosion inhibitor (benzotriazole) in its shell structure,and then were embedded into epoxy coatings to provide self-healing and anti-corrosion protection for carbon steel.Fast release of benzotriazole in acidic environment caused by local corrosion and the chelating effect of PDA-Fe3+ can synergistically promote the formation of protective film on bare steel surface,which endows coatings with self-healing func-tionality.Electrochemical impedance spectroscopy (EIS),local electrochemical impedance spectroscopy(LEIS),and spray tests were conducted to evaluate the active inhibition and corrosion resistance of the loaded coatings.The scratched coating with incorporation of nanocontainers presented better protection performance,exhibiting increased Ro (oxide layer resistance) and Rct (charge transfer resistance) during initial immersion periods.The EIS tests in long-term immersion were also performed to confirm the anti-corrosion effect of composited coatings.These results demonstrated that benzotriazole-decorated PDA capsules dramatically enhanced the self-healing properties and anti-corrosion performance of epoxy coatings with the synergistic help of PDA and benzotriazole.     

Corrosion protection of cold-rolled steel with alkyd paint coatings composited with submicron-structure types polypyrrole-modified nano-size alumina and carbon nanotubes

This paper is focused on studying corrosion protection of cold-rolled steel with alkyd paint coatings comprising nano-size alumina and either polystyrene-sulphonate (PSS) modified or sulphonated multi-walled carbon nanotube (MWCNT) supported polypyrrole (PPy). Single layer coatings (in thickness of 40 ± 5 μm) comprising PPy deposited alumina and PSS modified MWCNT supported PPy afforded viable protection during the 1 M sodium chloride test. The coatings containing PSS modified and weakly sulphonated MWCNTs (at volume fractions of 9.9 × 10⁻⁴ and 2.5 × 10⁻⁴) with PPy volume fractions of 3.5 × 10⁻³ and 2.5 × 10⁻³ provided effective corrosion prevention during the 1 M sodium chloride and hydrochloric acid solution tests. While inhibitor particles were characterised by infrared spectroscopy, corrosion products formed at the paint–steel interface were studied by X-ray photoelectron spectroscopy. Apart from the electron microscopy observations, rheology study of three-dimensional structure of the inhibitor particles was performed in dispersions at similar compositions to those used for the paint formulations. Thus, protection mechanism relating to both types of immersion tests is discussed in terms of properties of the inhibitor particles and their microstructure in the coatings.     

Effect of nano Al pigment on the anti corrosive performance of waterborne epoxy coatings

This paper presents the results regarding the effect of nano aluminum powder pigment concentration on the protective properties of waterborne epoxy films in 3.5 wt pct NaCl solution. The anticorrosive performance of the coatings with 0.5, 1, and 3 wt pct pigments and none pigment were investigated using electrochemical impedance spectroscopy （EIS）, scanning electron microscopy （SEM） and Raman spectroscopy techniques. The results show that adding appropriate amount of nano-aluminium powder pigment can enhance the barrier properties of the epoxy coating, which is attributed to the surface effect of nanoparticles and the compatibility of the pigment with the waterborne epoxy coatings.     

Corrosion behavior of plasma sprayed ceramic and metallic coatings on carbon steel in simulated seawater

Al₂O₃, ZrO₂ and Ni60 coatings were produced on carbon steels by plasma spray. Ni60 was used as the bond coat in all the cases. The microstructure of these coatings was analyzed by scanning electron microscopy (SEM). The corrosion behavior of the plasma spray coated samples as well as uncoated samples was evaluated by open circuit potential (OCP) measurements, potentiodynamic polarization tests, and electrochemical impedance spectroscopy (EIS) in simulated seawater. The results showed that Ni60 coating protected carbon steels against the corrosion and plasma spraying ceramic powders on metallic coating improved the corrosion resistance of the coatings further. The corrosion resistance of the Al₂O₃ coating was superior to that of the ZrO₂ coating due to the relatively few defects in Al₂O₃ coating.     

Corrosion protection of NiNb metallic glass coatings for 316SS by magnetron sputtering

Metallic glasses (MGs) appear as promising anti-corrosion coating materials due to their microstructural and physicochemical advantages,Herein,we proposed magnetron sputtered NiNb thin film MG coatings(MGCs) with different structures and compositions for corrosion protection of 316 stainless steel in an aggressive saline environment.The properties of monolayered Ni50Nb50 and Ni60Nb40,as well as the mul-tilayered Ni50Nb50/Ni60Nb40 (at.％) MGCs,were characterized in terms of morphology and microstructural properties,as well as the anticorrosion behavior.All the NiNb MGCs presented compact structure and the monolayered coatings exhibited preferable adhesion properties in comparison with the multilayered coating.The electrochemical tests and XPS results imply that the monolayered Ni50Nb50 MGC with high Nb content resisted corrosion mainly due to the formation of stable passive film that contained abun-dant Nb2O5 species,whereas the Ni60Nb40 MGC with high Ni content showed week corrosion protection performance during long-term service due to the dissolution of Ni cations and the devastation of the coating structure.Though with bit worse adhesion and more vulnerable Ni60Nb40 layers,the multilay-ered Ni50Nb50/Ni60Nb40 MGC possessed comparable corrosion resistance with the monolayered Ni50Nb50 MG coating,which remained stable even after 32 days of exposure.Such performance should be ascribed to the combined eff ;ect of the repassivation property for the sub-layers,the hindrance of propagation paths of micro-defects,and the obstruction of corrosive species by interfaces in the multilayered coating.     

Electrochemical behavior of nano-iron oxide modified alkyd based waterborne coatings

A nano-composite coating was formed using nano-Fe₂O₃ as pigments in different concentrations, to a specially developed alkyd based waterborne coating. The nano-Fe₂O₃ based composite coatings were applied on mild steel substrate by dipping. The dispersion of nano-Fe₂O₃ particles in coating system was investigated by SEM and AFM techniques. The effect of addition of these nano-pigments on the electrochemical behavior of the coating was investigated in 3.5% NaCl solution, using electrochemical impedance spectroscopy (EIS). Coating modified with higher concentration of nano-Fe₂O₃ particles showed comparatively better performance as it was evident from R_po and C_c values after 30 days of exposure. In general, the study showed an improvement in the corrosion resistance of the nano-particle modified coatings as compared to the neat coating, confirming the positive effect of nano-particle addition in coatings.     

Study on self-healing and corrosion resistance behaviors of functionalized carbon dot-intercalated graphene-based waterborne epoxy coating

Functionalized carbon dots(CDs)obtained from citric acid derivative were selected as intercalatorto modify graphene and then dispersed into epoxy matrix to prepare CDs modified graphene/epoxy(CDs-G/EP)coatings.Meanwhile,their microstructure,self-healing and corro sion resistance behaviors were analyzed deeply.Structural characterizations indicated the formation of"π-π"interaction between functionalized carbon dots and graphene.By observation,the dispersion and interface compatibility of graphene were greatly enhanced by CDs.The change rules of electrochemistry results implied that the addition of 0.5 wt.%CDs-G in EP coating(CDs-G0.5%/EP)demonstrated a superior protective property on steel,which was attributed to the physical barrier of highly dispersed graphene and the self-healing ability of CDs.After 50 days immersion,the oxygen permeability coefficient and water absorption of CDs-G0.5%/EP coating were only 4.27×10^-13cm³cm cm^-2s^-1Pa^-1 and 4.4%,respectively.     

Electrochemical, atomic force microscopy and infrared reflection absorption spectroscopy studies of pre-formed mussel adhesive protein films on carbon steel for corrosion protection

Electrochemical measurements, in situ and ex situ atomic force microscopy (AFM) experiments and infrared reflection absorption spectroscopy (IRAS) analysis were performed to investigate the formation and stability as well as corrosion protection properties of mussel adhesive protein (Mefp-1) films on carbon steel, and the influence of cross-linking by NaIO₄ oxidation. The in situ AFM measurements show flake-like adsorbed protein aggregates in the film formed at pH 9. The ex situ AFM images indicate multilayer-like films and that the film becomes more compact and stable in NaCl solution after the cross-linking. The IRAS results reveal the absorption bands of Mefp-1 on carbon steel before and after NaIO₄ induced oxidation of the pre-adsorbed protein. Within a short exposure time, a certain corrosion protection effect was noted for the pre-formed Mefp-1 film in 0.1 M NaCl solution. Cross-linking the pre-adsorbed film by NaIO₄ oxidation significantly enhanced the protection efficiency by up to 80%.     

Corrosion properties of titanium based hard coatings on steel

Titanium nitride TiN, titanium boronitride Ti(B,N) and titanium carbonitride Ti(C,N) coatings were deposited by PA-CVD on tempering and stainless steel substrates. The deposition process can be supervised by OES. The coatings were characterized XRD, SEM and WDS as well as hardness, adhesion and friction tests. Electrochemical impedance measurements and cyclic voltammetry in praxis relevant media were carried out. Mechanical and corrosion properties of the coatings can be controlled by the PA-CVD process parameters. The incorporation of chlorine in the coating can be varied by the process parameters with TiCl₄ or completely avoided using metallo-organic precursors. No influence of the chlorine content on the corrosion behavior was observed. Even coatings with extremely high chlorine content still exhibit an excellent corrosion resistance. Thus, the microstructure of the coating is the key to the corrosion properties of hard coatings on steel. A new micro electrochemical scanning droplet technique with a lateral resolution of 150 μm allows the investigation of TiN-coated substrates of complex geometry. The PA-CVD technique permits the deposition of dense and pinhole free coatings. On structures with simulated aspect ratios less than 3, a dense protective coating is proved. However, if the formation of micro pores is not suppressed by the optimal choice of deposition parameters, low-alloyed steel substrates corrode through pores, causing a detachment of the coating. On layers deposited on stainless steel, no sign of substrate corrosion could be detected. A model for the corrosion mechanism is given in Fig. 17.     

Corrosion behaviour of decorative and wear resistant coatings on steel deposited by reactive magnetron sputtering - Tests and improvements

Depositions of decorative and wear resistant single layer coatings like TiN, Ti(B,N), CrN, NbN, NbON, (Ti,Mg)N and multilayer coatings like Cr/CrN, Nb/NbN, CrN/NbN and NbN/Nb-C:H were performed using reactive magnetron sputtering. The corrosion behaviour of the coated high speed steel substrates was studied in sodium chloride containing media by open-circuit-potential measurements, potentiodynamic corrosion tests and salt spray tests. Up to now, the best improvements with respect to the corrosion resistance in salt spray tests could be obtained for the system (Ti,Mg)N/high speed steel.     

Simulation of sacrificial anode protection for steel platform using boundary element method

In the present paper, an offshore platform model dealing with sacrificial anode protection was simulated using boundary element method. The potential and current density were calculated, and the distribution trend of the data was analyzed. To evaluate the computation results, proper physical model was built in a given dimension. The physical platform model was placed in a marine environment modeling tank that was designed to simulate the real marine environment with seawater, and the calculation data were compared with those from laboratory experimental work. This study showed that the boundary element method is a powerful tool for the sacrificial anode protection of marine structures.     

Interactive Effects of Fly Ash and CNI on Corrosion of Reinforced High-Performance Concrete

The interactive effects of fly ash and CNI in corrosion of reinforced concrete were investigated. A 3⁴ full factorial design was developed considering water to cement ratio, fly ash percent, CNI and cracked condition as factors. The response factors were the weight loss calculated from Linear Polarization Resistance measurements and the pit depth of the steel bars embedded in concrete. Small-scale concrete slabs containing steel reinforcement with a cover depth of 20 mm were cast for this purpose. The slabs were subjected to a simulated marine environment with two cycles of wetting and drying per day during one year; after the exposure, the slabs were broken, the bars were cleaned and the pith depth measured by using SEM. Under the studied conditions, it was found that CNI alone does not provide corrosion protection of the steel reinforcement even for uncracked silica fume concrete in a 0.45 w/c ratio; however, the combination of CNI and fly ash can be useful to overcome this problem. The results indicate that low w/c ratio concrete in its crack state creates conditions suitable for the development of pitting corrosion.     

Corrosion resistance of tannic acid,d-limonene and nano-ZrO_2 modified epoxy coatings in acid corrosion environments

The protection of rusted carbon steel in acid corrosion environments is of great significance for equipment to keep safe operation.In this work,we presented a method to protect the rusted steel by ru st conversion treatment and epoxy coating.Tannic acid was selected as rust conversion agent.Tannic acid,D-limonene and nano-ZrO₂were used to improve the corrosion resistance of epoxy coatings.The Raman spectra,Xray diffraction and 3 D confocal images were used to characterize the rust conversion reaction.Ad hesion test showed that the loss of wet adhesion of the optimal coating was relatively low due to the addition of tannic acid,limonene and nano-ZrO(2).The corrosion resistance of five different coatings was investigated by scanning electron microscopy(SEM)and electrochemical analysis.Results show that after 264 h acid immersion,the low frequency resistance of the optimal coating consisting of rust conversion treatment and additives is 10⁷Ωcm²,three orders magnitude higher than that of the pristine coating.Moreover,SEM indicates that the optimal coating possesses a smooth surface and an unbroken interface between substrate and coating.Accordingly,the corrosion-resistant mechanism of the hybrid coating is proposed.     

Corrosion behaviour of hot dip zinc and zinc-aluminium coatings on steel in seawater

A comparative investigation of hot dip Zn-25Al alloy, Zn-55Al-Si and Zn coatings on steel was performed with attention to their corrosion performance in seawater. The results of 2-year exposure testing of these at Zhoushan test site are reported here. In tidal and immersion environments, Zn-25Al alloy coating is several times more durable than zinc coating of double thickness. At long exposure times, corrosion rate for the Zn-25Al alloy coating remains indistinguishable from that for the Zn-55Al-Si coating of similar thickness in tidal zone, and is two to three times lower than the latter in immersion zone. The decrease in tensile strength suggested that galvanized and Zn-55Al-Si coated steel suffer intense pitting corrosion in immersion zone. The electrochemical tests showed that all these coatings provide cathodic protection to the substrate metal; the galvanic potentials are equal to −1,050, −1,025 and −880 mV (SCE) for zinc, Zn-25Al alloy and Zn-55Al-Si coating, respectively, which are adequate to keep the steel inside the immunity region. It is believed that the superior performance of the Zn-25Al alloy coating is due to its optimal combination of the uniform corrosion resistance and pitting corrosion resistance. The inferior corrosion performance by comparison of the Zn coating mainly results from its larger dissolution rate, while the failure of the Zn-55Al-Si coating is probably related to its higher susceptibility to pitting corrosion in seawater.     

Synthesis of hybrid silica sol–gel coatings containing Zn particles on carbon steel and Al/Zn coated carbon steel

Owing to increasing interest of coatings applied on low alloy steel and galvanised metal plates and their applications, this work presents the study of the process requirements to be fulfilled in order to coat these metals with an hybrid silica coatings containing Zn particles. The main idea was to combine the “barrier” effect of the hybrid silica coatings with the “active protection” effect of the zinc particles inside the coatings. Sol–gel parameters, Zn particles content and suspension stability have been studied. EMPHOS ES 21, an electrostatic dispersant, has been used to obtain stabilised suspensions. Thick, adherent and crack-free coatings containing 10% Zn particles were prepared by dip-coating on carbon steel and Al/Zn coated carbon steel substrates. The applied coating seems to improve corrosion protection of the two metal substrates, and this effect is more noticeable in the case of the Al/Zn system because of the combination of the complementary corrosion protection properties of both coatings.     

Effect of carbon nanotube modified epoxy adhesive on CFRP-to-steel interface

The effects of carbon nanotube (CNT) modified epoxy adhesive on CFRP-to-steel interfaces were investigated using double strap joints. The bond behaviours studied were failure modes, bond interface at microlevel, bond strength, effective bond length, CFRP strain distribution and bond-slip relationships.For the first time, a novel type of failure in the CFRP-steel joint was discovered, attributable to weak bonding between woven mesh and CFRP fibres. This failure mode prevented exploitation of the full potential of the carbon fibres and the CNT modified epoxy adhesive. Joints bonded with CNT-epoxy adhesive had an effective bond length of about 60 mm, whereas that of joints bonded with pure epoxy was about 70 mm. The CNT-epoxy adhesive can transfer more load from the host structure to the bonded CFRP laminates, consequently modifying bond behaviour. It is therefore expected that CNT-epoxy nanocomposites will assist in the strengthening and rehabilitation of steel infrastructures using CFRP laminates.     

Influence of LDH conversion coatings on the adhesion and corrosion protection of friction spot-joined AA2024-T3/CF-PPS

Layered double hydroxide(LDH)conversion coatings loaded with corrosion inhibitors were suggested for the surface treatment of the aluminum alloy 2024-T3,prior to friction spot joining with carbon-fiber reinforced polyphenylene sulfide(AA2024-T3/CF-PPS).Vanadate was used as a model corrosion inhibitor.Lap shear testing method revealed an increase of approx.20%of the joint’s adhesion performance when treated with LDH and before exposure to salt spray.The evaluation of the joints after exposure to salt spray demonstrated a significant difference in the corrosion behavior of the joints when the AA2024-T3 is treated with LDH loaded with nitrate and vanadate species.The LDH intercalated with nitrate revealed a clear improvement in the mechanical and corrosion resistance performance of the joints,even after 6 weeks of salt spray.However,the LDH intercalated with vanadate failed in providing protection against corrosion as well as preserving the mechanical properties of the joints.The effect of the galvanic corrosion was further investigated by zero resistance ammeter(ZRA)measurements as well as localized scanning vibrating electrode technique(SVET).     

Highly dispersed polyaniline/graphene oxide composites for corrosion protection of polyvinyl chloride/epoxy powder coatings on steel

Journal of Materials Science - In this study, a novel functionalized graphene oxide(GO) sheet of polyaniline(PANI) was prepared by in situ polymerization of aniline. Fourier transform infrared...     

Corrosion resistance of electrodeposited Ni–Al composite coatings on the aluminum substrate

Ni matrix–Al particle composite coating was adopted via sediment co-deposition (SCD) method on the zincate coated aluminum substrate. Surface morphology was investigated by scanning electron microscopy (SEM). The electrochemical behavior of the coatings was studied by polarization potentiodynamic test in 3.5 wt.% sodium chloride using a three electrode open cell. The effect of the electroplating parameters on the Al co-deposition was studied. Maximum of 22 wt.% Al particles were deposited in the coating. It was found that the zincate coating plays an important role in improving the nickel layer adherent. Furthermore, incorporation of aluminum particles in Ni matrix refined the Ni crystal coatings. However, polarization curves shifted to negative potentials and corrosion rate is decreased.     

Corrosion resistance of biomimetic calcium phosphate coatings on magnesium due to varying pretreatment time

Calcium phosphate coatings were prepared on magnesium substrates via a biomimetic coating process. The effects of a magnesium hydroxide pretreatment on the formation and the ultimate corrosion protection of the coatings were studied. The pretreatment layer was found to affect the amount of defects present in the coatings. Corrosion resistance of the coatings was studied in vitro using two simulated body fluids, 0.8% NaCl and Hanks solution. In NaCl, the resistance to corrosion of all samples decreases with time as corrosion proceeded through cracks and other defects in the coatings. Samples with no pretreatment displayed the highest corrosion resistance as these samples had the fewest defects in the coating. However, in Hanks solution, corrosion resistance increased with time due to additional nucleation of calcium phosphate from the fluid on to the substrate. In this solution, additional pretreatment time was beneficial to the overall corrosion resistance.