Advanced anticorrosive coatings prepared from electroactive epoxy–SiO2 hybrid nanocomposite materials

A series of electroactive epoxy/amino-SiO₂ nanocomposite materials containing conjugated segments of electroactive amino-capped aniline trimer (ACAT) unit were successfully prepared. First of all, the amino-modified silica (AMS) particles of ∼50 nm in diameter were synthesized by performing the conventional base-catalyzed sol–gel reactions of tetraethyl orthosilicate (TEOS) in the presence of (3-aminopropyl)-trimethoxysilane (APTES) molecules. Subsequently, the AMS nanoparticles were blended into the epoxy ring-opening polymerization reactions between amino-terminated aniline trimer (ACAT)/T-403 and DGEBA, leading to the formation of electroactive epoxy resin–silica hybrid nanocomposites (EES). Furthermore, the redox behavior of as-prepared EES materials was identified by the electrochemical cyclic voltammetry studies. It should be noted that the as-prepared electroactive hybrid materials in the form of coating on cold-rolled steel (CRS) electrode were found to be much superior in corrosion protection over those of non-electroactive epoxy (NEE) and electroactive epoxy (EE) materials based on a series of electrochemical corrosion measurements in saline. The possible mechanism for the advanced enhancement of corrosion protection of EES coatings on CRS electrode could be interpreted as follows: (1) electroactive epoxy coatings may act as physical barrier coating; (2) redox catalytic capabilities of ACAT units existed in electroactive epoxy may induce the formation of passive metal oxide layers on CRS electrode, as further evidenced by SEM and ESCA studies; (3) well-dispersed AMS nanoparticles in EES matrix could act as effective hinder to enhance the oxygen barrier property of electroactive epoxy matrix, the result could be demonstrated by gas permeability analysis (GPA). Electroactive epoxy/SiO₂ nanocomposites were identified by a series of electrochemical measurements such as corrosion potential (E_corr), polarization resistance (R_p), corrosion current (I_corr) and electrochemical impedance spectroscopy (EIS) studied in 5 wt% NaCl electrolyte.     

Advanced anticorrosive materials prepared from amine-capped aniline trimer-based electroactive polyimide-clay nanocomposite materials with synergistic effects of redox catalytic capability and gas barrier properties

In this study, preparation and electrochemical corrosion protection studies of a series of polyimide-Clay nanocomposite (PCN) materials were first presented. Subsequently, the as-prepared PCN materials were characterized by FTIR, XRD and TEM studies. In-situ monitoring for redox behavior of as-prepared PCN materials was identified by UV-visible and CV studies.It should be noted that PCN coating was found to reveal advanced corrosion protection effect on cold-rolled steel (CRS) electrode as compared to that of neat non-electroactive polyimide coating based on series of electrochemical corrosion measurements in 5 wt% NaCl electrolyte. Enhancement of corrosion protection of PCN coatings on CRS electrode may be interpreted by following two possible reasons: (1) redox catalytic capabilities (i.e., electroactivity) of ACAT units existed in electroactive PCN may induce formation of passive metal oxide layers on CRS electrode, as evidenced by SEM and ESCA studies. (2) well-dispersed layered organophilic clay platelets embedded in electroactive PCN matrix could functioned as hinder with high aspect ratio to effectively enhance the oxygen barrier property of PCN, as evidenced by GPA.     

Electrochemical studies on aniline-pentamer-based electroactive polyimide coating: Corrosion protection and electrochromic properties

In this study, electrochemical investigations of corrosion protection and the electrochromic properties of an aniline-pentamer-based electroactive polyimide (AP-based EPI) coating prepared by oxidative coupling polymerization are presented. The in situ chemical oxidation of the reduced form of soluble, electroactive poly(amic acid) (EPAA) in N-methyl-2-pyrrolidone (NMP) was monitored by UV–Vis absorption spectra. Moreover, the electroactivity of the AP-based EPI was evaluated by performing electrochemical CV studies. Based on a series of electrochemical measurements in 3.5 wt% NaCl electrolyte, the AP-based EPI coating was found to exhibit enhanced corrosion protection effects on cold-rolled steel (CRS) electrodes as compared to the corresponding non-electroactive (NEPI) coating. A possible mechanism for the enhanced corrosion protection of EPI coatings on the CRS electrode has been proposed as follows: (1) EPI coatings may act as a physical barrier and (2) the redox catalytic properties of the aniline pentamer units in EPI may induce the formation of a passive metal oxide layer on the CRS electrode, as evidenced by SEM and ESCA studies. The electrochromic performance of EPI was investigated by measuring electrochromic photographs and UV absorption spectra.     

Synthesis and anticorrosive properties of electroactive polyimide/SiO2 composites

In this study, a series of electroactive polyimide/SiO₂ (EPIS) composite materials containing conjugated segments of electroactive amino‐capped aniline trimer (AT) unit were successfully prepared. First of all, the amino‐modified silica (AMS) particles of ∼100 nm in diameter were synthesized by performing the conventional base‐catalyzed sol–gel reactions. Subsequently, the AMS nanoparticles were blending into the polymerization reactions between AT and 4,4′‐(4,4′‐isopropylidenediphenoxy)‐bis(phthalic anhydride), leading to the formation of EPIS composites. The as‐prepared EPIS materials in the form of coating on cold‐rolled steel (CRS) electrode were found to be much superior in corrosion protection over those of non‐electroactive polyimide and EPI materials based on a series of electrochemical corrosion measurements in saline. The significant enhancement in corrosion protection of EPIS coatings on CRS electrodes might probably be attributed to the redox catalytic property of organic EPI inducing the formation of passive metal oxide layer and the barrier property of well‐dispersed AMS nanoparticles existed in EPI matrix. POLYM. COMPOS., 35:617–625, 2014. © 2013 Society of Plastics Engineers     

Effect of amino-capped aniline trimer on corrosion protection and physical properties for electroactive epoxy thermosets

A series of electroactive epoxy thermosets (EETs) containing conjugated segments of electroactive amino-capped aniline trimer (ACAT) unit were successfully prepared and characterized. Furthermore, the redox behavior of as-prepared EET materials was identified by the electrochemical cyclic voltammetry studies. Higher concentration of ACAT component in as-prepare corresponding EETs was found to lead to an remarkably enhanced corrosion protection effect on cold-rolled steel (CRS) electrode based on sequential electrochemical corrosion measurements in 5 wt% NaCl supporting electrolyte. Mechanism for the enhancement of corrosion protection of EET coatings on CRS electrode might be attributed to the redox catalytic capabilities of ACAT units existed in EETs, leading to the formation of passive metal oxide layers, as further evidenced by SEM and ESCA studies. Effect of material composition on thermal stability and mechanical strength of EETs were also investigated by TGA, DSC and DMA, respectively.     

Photogenerated cathodic protection and invalidation of silane/TiO<Subscript>2</Subscript> hybrid coatings

Silane/TiO₂ hybrid coatings were prepared on 304 stainless steel (304 SS) by a simple dipping method, where the silane is d-γ-methylacryloxy propyl trimethoxyl silane (CH₂=C(CH₃)COO(CH₂)₃Si(OCH₃)₃, MPMS). The photogenerated cathodic protection and invalidation of the hybrid coatings were evaluated by microstructure and electrochemical characterization. The coupling agent MPMS reduced the agglomeration of the nanosized TiO₂ powders and promoted the adhesion of the coatings. Barrier protection of the coupled metal was promoted for the hybrid coatings in a short corrosion time. However, MPMS decreased the carrier concentration of the TiO₂ electrode due to the large interface resistance. As a result, the corrosion potential shifted positively and the photogenerated cathodic protection decreased. In long-time corrosion, the hybrid coatings became invalid because of the accumulation of electropositive holes that may weaken the Ti–O bond and destroy the barrier effect.     

Enhanced anticorrosion coatings prepared from incorporation of well‐dispersed silica nanoparticles into fluorinated polyimide matrix

Series of advanced anticorrosive hybrid coatings comprising of organo‐soluble fluorinated polyimide (SFPI) matrix dispersed with different feeding ratio of inorganic silica (SiO₂) nanoparticles has been successfully prepared through a conventional chemical imidization of polyimide and acid catalyzed sol–gel process of TEOS. It should be noted that the incorporation of SiO₂ nanoparticles into the SFPI matrix can effectively enhance the corrosion protection performance on cold‐rolled steel (CRS) electrode against corrosive species in saline condition when compared with that of neat polymeric coatings based on a series of standard electrochemical corrosion measurements, such as corrosion potential, polarization resistance, corrosion current, and impedance spectroscopy. POLYM. COMPOS., 31:2025–2034, 2010. © 2010 Society of Plastics Engineers     

In-situ generation and application of nanocomposites on steel surface for anti-corrosion coating

Thin organic coatings directly on steel sheets provide excellent barrier protection in saline environment and meet deformability demands, but fail in providing active corrosion protection. We have put an effort to solve this problem by formulating composite coatings using in-situ generation of metal oxide nanoparticles (NPs) in the polymer matrix. Here we present a new synthesis method of high performance polyetherimide composite with TiO₂, MgO, and Al₂O₃ nanoparticles and their application for anti-corrosion coatings in saline environment. We observed that in-situ synthesis of these metal oxide NPs in the polymer curing process leads to evenly distribution and uniform size of nanoparticles. Thermo-mechanical property was analyzed for these three kinds of free-standing composite film to assess elasto-plastic behaviour and compared to mother polymer film. Results indicated that thermal stability and elastic behaviour of composites film are not affected to the great extent by the presence of NPs. The potentiodynamic and the electrochemical impedance studies on these composite coated steel panels were carried out to identify active–passive behaviour. Results showed active corrosion protection from nanocomposite coating based on TiO₂ and barrier protection was noticed from nanocomposite coating based on MgO and Al₂O₃.     

A study on the N-, S- and Cl-modified nano-TiO2 coatings for corrosion protection of stainless steel

Nano-titania coatings doped with anions of nitrogen, sulfur and chlorine have been supplied on the surface of 316L stainless steel by a sol-gel process and dip-coating technique. The measurements of XRD, SEM, ATR-IR, Raman and XPS were carried out to characterize the chemical composition and structure for the prepared samples. The corrosion performances of the coating in 0.5 M NaCl were evaluated by electrochemical impedance spectroscopy (EIS) and polarization measurements. According to the measurements of EIS and electrochemical polarization, the N-modified TiO₂ nano-coatings show a highest corrosion resistance among the prepared coatings. It is revealed, from the SEM, XRD and Raman characterizations, that the surface of N-modified TiO₂ nano-coatings are more compact and uniform, relatively well-crystallized and able to act as an optimal barrier layer to metallic substrates. The XPS analysis confirms the presence of low concentration of N element in two forms, atomic β-N (interstitial state) and chemisorbed γ-N₂ on the surface of TiO₂ nano-coatings. It is suggested that the addition of nitrogen is beneficial to improve the compact structure and enhance the hydrophobic property.     

Synthesis of polypyrrole/Ni-doped TiO2 nanocomposites (NCs) as a protective pigment in organic coating

This study reports the synthesis of polypyrrole/Ni-doped TiO₂ nanocomposites (NCs) as a protective pigment in organic coatings. Polypyrrole/Ni-doped TiO₂ NCs were prepared by in situ chemical oxidative polymerization of pyrrole monomer in the presence of Ni-doped TiO₂ nanoparticles (NPs) with ammonium persulfate (APS) as oxidant. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) result show a core–shell structure of the pigments. The XRD results indicate that the average crystalline size of Ni-doped TiO₂ NPs is larger than TiO₂ NPs while the sizes of polypyrrole/TiO₂ NCs and polypyrrole/Ni-doped TiO₂ NCs were 93.46 ± 0.06 and 26.16 ± 0.06 nm respectively. Hence the thickness of the shell in the core–shell incorporating the Ni-doped/TiO₂ NPs was very thin and the area of synthesized PPy is increased. The electrochemical impedance spectroscopy (EIS) results show that increasing the area of synthesized polypyrrole in the presence of Ni-doped-TiO₂ NPs can increase its ability to interact with the ions liberated during the corrosion reaction of steel in the presence of NaCl.     

Synthesis,characterization and corrosion protection of poly-4-methyl-3-mercapto-1,2,4-triazole/TiO2 composite on copper

The present work deals with the electrochemical synthesis of poly-4-methyl-3-mercapto-1,2,4-triazole (p-MMTA)/TiO₂ composite on metallic copper to evaluate its corrosion protection. The composite was characterized by FT-IR, cyclic voltammetry, X-ray diffraction and energy dispersive X-ray analysis. The distribution of inorganic particles in the polymeric matrix was evidenced from the scanning electron microscopic studies. The corrosion performance of composite coating was evaluated by electrochemical impedance spectroscopy and Tafel polarization measurements in 3.5 % NaCl medium. The p-MMTA/TiO₂ composite showed an excellent corrosion protection ability, which was evidenced from the results of electrochemical measurements. The enhanced ability could be due to the barrier effect of composite coatings against corrosive species and also due to the synergistic effect between organic polymer and inorganic particles.     

Styrene butadiene co-polymer based conducting polymer composite as an effective corrosion protective coating

Electroactive conducting polymer composite coatings of polyaniline (PANI) are electrosynthesized on styrene–butadiene rubber (SBR) coated stainless steel electrode by potentiostatic method using aqueous H₂SO₄ as supporting electrolyte. The protective behaviour of these coatings in different corrosion media (3.5% NaCl and 0.5 M HCl) is investigated using Tafel polarization curves, open circuit potential measurements and electrochemical impedance spectroscopy. The results reveal that SBR/PANI composite coating is much better in corrosion protection than simple PANI coating. The corrosion potential of composite films shifts to more noble values indicating that SBR/PANI composite coating act as an effective corrosion protective layer.     

Conducting polyaniline-nano-TiO2 composites for smart corrosion resistant coatings

Coatings prepared from polyaniline-nano-TiO₂ particles synthesized by in situ polymerization were found to exhibit excellent corrosion resistance much superior to polyaniline (PANI) in aggressive environments. The corrosion studies were carried out on steel plates coated with these formulations containing 10 wt% polyaniline prepared with different concentrations of nano-TiO₂. The electrochemical impedance spectroscopy was studied at periodic intervals during exposure to hot saline (65 °C) conditions for prolonged durations over a period of 90 h. The open circuit potential (OCP) was found to shift with time from −0.38 V SCE to more anodic side (−0.2 V SCE) much above that of bare steel (−0.5 V SCE). The presence of nano-TiO₂ was found to be vital in the prevention of corrosion and the shift of OCP to anodic side. From these data, one could envisage more than 100 times improvement in the corrosion resistance especially for polyaniline prepared with 4.18 wt% nano-TiO₂. The exceptional improvement of performance of these coatings has been associated with the increase in barrier to diffusion, prevention of charge transport by the nano-size TiO₂, redox properties of polyaniline as well as very large surface area available for the liberation of dopant due to nano-size additive.     

Investigation of photoelectrocatalytic activity of Cu2O nanoparticles for p-nitrophenol using rotating ring-disk electrode and application for electrocatalytic determination

A cuprous oxide (Cu₂O) nanoparticles modified Pt rotating ring-disk electrode (RRDE) was successfully fabricated, and the electrocatalytic determination of p-nitrophenol (PNP) using this electrode was developed. Cu₂O nanoparticles were obtained by reducing the copper-citrate complex with hydrazine hydrate (N₂H₄·H₂O) in a template-free process. The hydrodynamic differential pulse voltammetry (HDPV) technique was applied for in situ monitor the photoelectrochemical behavior of PNP under visible light using nano-Cu₂O modified Pt RRDE as working electrode. PNP undergoes photoelectrocatalytic degradation on nano-Cu₂O modified disk to give electroactive p-hydroxylamino phenol species which is compulsive transported and can only be detected at ring electrode at around 0.05 V with oxidation signal. The effects of illumination time, applied bias potential, rotation rates and pH of the reaction medium have been discussed. Under optimized conditions for electrocatalytic determination, the anodic current is linear with PNP concentration in the range of 1.0 × 10⁻⁵ to 1.0 × 10⁻³ M, with a detection limit of 1.0 × 10⁻⁷ M and good precision (RSD = 2.8%, n = 10). The detection limit could be improved to 1.0 × 10⁻⁸ M by given illumination time. The proposed nano-Cu₂O modified RRDE can be potentially applied for electrochemical detection of p-nitrophenol. And it also indicated that modified RRDE technique is a promising way for photoelecrocatalytic degradation and mechanism analysis of organic pollutants.     

The synergistic combination of bis-silane and CeO2·ZrO2 nanoparticles on the electrochemical behaviour of galvanised steel in NaCl solutions

Bis-1,2-[triethoxysilylpropyl]tetrasulfide silane films containing CeO₂·ZrO₂ nanoparticles were deposited by dip-coating on galvanised steel substrates. The morphological features of the coated substrates were evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The anti-corrosion performance of the modified silane film applied on galvanised steel substrates was studied by electrochemical impedance spectroscopy (EIS). The ability of nanoparticles to mitigate localized corrosion activity at artificially induced defects was investigated via the scanning vibrating electrode technique (SVET) and by the scanning ion-selective electrode technique (SIET). The results showed that the addition of nanoparticles provides good corrosion protection of the galvanised steel substrates pre-treated with the modified silane solutions. The corrosion activity was reduced by more than one order of magnitude. Complementary d.c. experiments, using zinc electrodes exposed to NaCl solutions containing the nanoparticles were also performed in order to better understand the role of the nanoparticles. An ennoblement of the corrosion potential and polarisation of the anodic reactions could be detected.     

Electrochemical investigations on the corrosion protection effect of poly(vinyl carbazole)‐silica hybrid sol–gel materials

A series of sol–gel derived organic–inorganic hybrid coatings consisting of organic poly (vinyl carbazole) (PVK) and inorganic silica (SiO₂), with 3‐(trimethoxysilyl)propyl methacrylate (MSMA) as coupling agent, were successfully synthesized. First of all, vinyl carbazole (VCz) monomers are copolymerized with MSMA by performing free‐radical polymerization reactions with AIBN as initiator. Subsequently, as‐prepared copolymer (i.e., sol–gel precursor) was further reacted with various feeding content of tetraethyl orthosilicate (TEOS) through organic acid (CSA)‐catalyzed sol–gel reaction to form a series of PVK‐silica hybrid (PSH) sol–gel materials. The as‐synthesized hybrid materials were subsequently characterized by Fourier‐Transformation infrared (FTIR) spectroscopy and solid‐state ²⁹Si NMR. It should be noted that the PVK‐SiO₂ hybrid (PSH) coating on cold‐rolled steel (CRS) electrode with low silica loading (e.g., 10 phr) was found to be superior in anticorrosion property over those of neat PVK based on a series of electrochemical measurements such as corrosion potential, polarization resistance, corrosion current, and electrochemical impedance spectroscopy in 3.5 wt% NaCl electrolyte. The better anticorrosion performance of PSH coatings as compared to that of neat polymer may probably be attributed to the stronger adhesion strength of PSH coatings on CRS electrode, which was further evidenced by Scotch tape test evaluation. Increase of adhesion strength of PSH coatings on CRS electrode may be associated with the formation of Fe–O–Si covalent bonds at the interface of PSH coating and CRS electrode based on the FTIR–RAS (reflection absorption spectroscopy) studies. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Influence of natural inhibitor,pigment and extender on corrosion of polymer coated steel

Lupine (Lupinous albus L.) seeds extract was incorporated into a vinyl chloride–vinyl acetate copolymer based paint formulation to control steel corrosion in 0.5 M NaCl. Evaluation of this system included the use of electrochemical impedance spectroscopy (EIS) and a salt spray cabinet for accelerated aging tests. The EIS data demonstrated that highest protection was attained at a lupine threshold concentration of 0.025 g/L. Two white color pigments (ZnO and TiO₂) and three extenders (CaCO₃, mica and talc) were tested as paint additives. The accelerated aging tests showed that the coated steel panels containing TiO₂ had a high degree of blistering while those containing ZnO exhibited reasonable hiding power and better protection efficiency. Field tests indicated that the presence of TiO₂ enhanced the growth of fouling organisms over the coated steel surface.     

Microstructure effects on the electrochemical corrosion of carbon materials and carbon-supported Pt catalysts

The electrochemical corrosion behavior of a set of porous carbonaceous materials of interest as catalyst supports for polymer electrolyte membrane fuel cells was examined in 2 M H₂SO₄ at 80 °C at constant electrode potential of 1.2 V vs. RHE. Correlations have been observed between the specific rates of corrosion of carbon materials and carbon-supported Pt catalysts on the one hand and their substructural characteristics derived from X-ray diffraction analysis on the other hand. Carbon supports of the Sibunit family and catalytic filamentous carbons possess lower specific (i.e., surface area normalized) corrosion currents compared to conventional furnace black Vulcan XC-72 and better stabilize Pt nanoparticles.     

Cerium salt activated nanoparticles as fillers for silane films: Evaluation of the corrosion inhibition performance on galvanised steel substrates

The present work investigates the electrochemical behaviour of galvanised steel substrates pre-treated with bis-[triethoxysilylpropyl] tetrasulfide silane (BTESPT) solutions modified with SiO₂ or CeO₂ nanoparticles activated with cerium ions. The electrochemical behaviour of the pre-treated substrates was evaluated via electrochemical impedance spectroscopy in order to assess the role of the nanoparticles in the silane film resistance and capacitance. The ability of the Ce-activated nanoparticles to mitigate corrosion activity at the microscale level in artificial induced defects was studied via scanning vibrating electrode technique (SVET). Complementary studies were performed using potentiodynamic polarisation. The results show that the presence of nanoparticles reinforces the barrier properties of the silane films and that a synergy seems to be created between the activated nanoparticles and the cerium ions, reducing the corrosion activity. The addition of CeO₂ nanoparticles was more effective than the addition of SiO₂ nanoparticles.     

Chemical composition and corrosion protection of silane films modified with CeO2 nanoparticles

The present work aims at understanding the role of CeO₂ nanoparticles (with and without activation in cerium(III) solutions) used as fillers for hybrid silane coatings applied on galvanized steel substrates.The work reports the improved corrosion protection performance of the modified silane films and discusses the chemistry of the cerium-activated nanoparticles, the mechanisms involved in the formation of the surface coatings and its corrosion inhibition ability.The anti-corrosion performance was investigated using electrochemical impedance spectroscopy (EIS), the scanning vibrating electrode technique (SVET) and d.c. potentiodynamic polarization. The chemical composition of silanised nanoparticles and the chemical changes of the silane solutions due to the presence of additives were studied using X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance spectroscopy (NMR), respectively.The NMR and XPS data revealed that the modified silane solutions and respective coatings have enhanced cross-linking and that silane-cerium bonds are likely to occur.Electrochemical impedance spectroscopy showed that the modified coatings have improved barrier properties and the SVET measurements highlight the corrosion inhibition effect of ceria nanoparticles activated with Ce(III) ions. Potentiodynamic polarization curves demonstrate an enhanced passive domain for zinc, in the presence of nanoparticles, in solutions simulating the cathodic environment.