Corrosion protection coating containing polyaniline glass flake composite for steel

Corrosion protection of steel by glass flake (GF) containing coatings is widely used in marine atmosphere. Even though, the coatings containing glass flake are highly corrosion resistant, their performance is decreased due to the presence of pinholes and coating defects. It is well established that polyaniline containing coating is able to protect the pinhole defects in the coatings due to passivating ability of polyaniline. Hence a study has been made on the corrosion protection ability of steel using polyaniline-glass flake composite containing coating with 10% loading of glass flake in epoxy binder. The polyaniline glass flake composite (PGFC) was synthesized by chemical oxidation of aniline by ammonium persulphate in presence of glass flake. The corrosion protection ability of GF and PGFC containing coating on steel was found out by salt spray test and EIS test in 3% NaCl. In both the tests, the resistance value of the PGFC containing coating has remained at 10⁸-10⁹ Ω cm² where as for the GF containing coating, the resistance values decreased to 10⁵ Ω cm². The enhanced corrosion protection ability of the PGFC containing coating is due to the passivation ability of the polyaniline present in the coating.     

A new corrosion protection coating with polyaniline-TiO2 composite for steel

Organic coating strategies for corrosion protection with inherently conducting polymers have become important because of restriction on the use of heavy metals and chromates in coatings due to their environmental problems. This work presents the synthesis of polyaniline-TiO₂ composites (PTC) and the corrosion protection behaviour of PTC containing coating on steel. PTC was prepared by chemical oxidation of aniline and TiO₂ by ammonium persulfate in phosphoric acid medium. The PTC was characterized by FTIR, XRD and SEM techniques. Suitable coating with PTC was formed on steel using acrylic resin. Using electrochemical impedance spectroscopy, the PTC containing coating's behaviour in 3% NaCl immersion test and salt spray test has been found out. Results indicate that the coating containing PTC is able to maintain the potential of steel in passive region due to its redox property. The resistance of the coating containing PTC was more than 10⁷ Ω cm² in 3% NaCl solution after 60 days and 10⁹ Ω cm² in the salt spray test of 35 days. But the resistance of the TiO₂ containing coating was found to be less than 10⁴ Ω cm² in both the cases. The high performance of PTC containing coating is attributed to the passivation of steel by polyaniline.     

Electrochemical polymerization and initial corrosion properties of polyaniline-benzoate film on aluminum

Electrochemical synthesis of polyaniline (PANI) on aluminum electrode from aqueous solution of 0.25 mol dm⁻³ aniline and 0.2 mol dm⁻³ sodium benzoate has been investigated under potentiodynamic and galvanostatic conditions. Initial corrosion behavior of aluminum and PANI coated aluminum electrode exposed to 3% NaCl has been investigated using electrochemical potentiodynamic and impedance spectroscopy technique (EIS). It was shown that PANI coating initially provide corrosion protection of aluminum, decreasing the corrosion current density at least 15 times.     

Conductive hybrid film from polyaniline and polyurethane-silica

In order to improve the mechanical performance and water resistance of water-borne conducting polyaniline film, conducting polyaniline/polyurethane-silica hybrid film was prepared in aqueous solution employing silanol-terminated polyurethane and methyltriethoxysilane as sol-gel precursors. The hybrid film showed surface resistivity of 10⁸ Ω even though the conducting polyaniline loading was only 10 wt% (or 1.5 wt% of polyaniline), and the mechanical performance as well as water resistance was significantly improved, making it suitable for antistatic application. Therefore, a practical route to water-borne processing of conducting polyaniline is disclosed.     

Protective properties of intact unpigmented epoxy coated mild steel under cathodic protection

Electrochemical Impedance Spectroscopy (EIS) has been used to characterise intact unpigmented epoxy coated mild steel with and without the application of cathodic protection (CP). Coated specimens were exposed to 0.6 M NaCL solution. Cathodic protection was applied at −0.78 V and −1.1 V (SCE). Coated specimens were also tested at Open Circuit Potential (OCP). The application of cathodic protection at −1.1 V was shown to affect the protective properties of the coating, causing the coating resistance to fall below the border line between fair and poor coating. The coating maintained a resistance in the order of 1 × 10⁶ Ω cm² when CP was applied at −0.78 V but a resistance of 1 × 10⁵ Ω cm² when CP was applied at −1.1 V. It was shown that water uptake by the coated specimens was considerably affected by the application of CP. The water uptake by the coated specimens was increased as a result of increasing the level of CP. The application of CP at −0.78 V, and −1.1 V was found to reduce the extent of corrosion on the coated specimens.     

Multi-wall carbon nanotubes coated with polyaniline

Multi-wall carbon nanotubes (CNT) were coated with protonated polyaniline (PANI) in situ during the polymerization of aniline. The content of CNT in the samples was 0-80 wt%. Uniform coating of CNT with PANI was observed with both scanning and transmission electron microscopy. An improvement in the thermal stability of the PANI in the composites was found by thermogravimetric analysis. FTIR and Raman spectra illustrate the presence of PANI in the composites; no interaction between PANI and CNT could be proved. The conductivity of PANI-coated CNT has been compared with the conductivity of the corresponding mixtures of PANI and CNT. At high CNT contents, it is not important if the PANI coating is protonated or not; the conductivity is similar in both cases, and it is determined by the CNT. Polyaniline reduces the contact resistance between the individual nanotubes. A maximum conductivity of 25.4 S cm⁻¹ has been found with PANI-coated CNT containing 70 wt% CNT. The wettability measurements show that CNT coated with protonated PANI are hydrophilic, the water contact angle being ∼40°, even at 60 wt% CNT in the composite. The specific surface area, determined by nitrogen adsorption, ranges from 20 m² g⁻¹ for protonated PANI to 56 m² g⁻¹ for neat CNT. The pore sizes and volumes have been determined by mercury porosimetry. The density measurements indicate that the compressed PANI-coated CNT are more compact compared with compressed mixtures of PANI and CNT. The relaxation and the growth of dimensions of the samples after the release of compression have been noted.     

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.     

Electropolymerized polyaniline coatings on aluminum alloy 3004 and their corrosion protection performance

Homogeneous and adherent polyaniline coatings were electrosynthesized on aluminum (Al) alloy 3004 (AA 3004) from an aqueous solution containing aniline and oxalic acid by using the galvanostatic polarization method. A higher applied current density in the polymerization stage proved to be the best condition to adopt for the synthesis of more compact and strongly adherent polyaniline coatings on Al. The corrosion performances of polyaniline coatings were investigated in 3.5% NaCl solution by the potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS).Potentiodynamic polarization and electrochemical impedance spectroscopy studies reveal that the polyaniline acts as a protective layer on Al against corrosion in 3.5% NaCl solution. The current corrosion decreases significantly from 6.55 μA cm⁻² for uncoated Al to 0.158 μA cm⁻² for polyaniline-coated Al. The corrosion rate of the polyaniline-coated Al is found to be 5.17 × 10⁻⁴ mm year⁻¹, which is ∼40 times lower than that observed for bare Al. The potential corrosion increases from −1.015 V versus SCE for uncoated Al to ∼−0.9 V versus SCE for polyaniline-coated Al electrodes. The positive shift of ∼0.11 V in potential corrosion indicates the protection of the Al surface by the polyaniline coatings.The synthesized coatings were characterized by UV-visible absorption spectrometry, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Optical absorption spectroscopy reveals the formation of the emeraldine form of polyaniline. The results of this study clearly ascertain that the polyaniline has outstanding potential to protect the AA 3004 alloy against corrosion in a chloride environment.     

Poly(methyl methacrylate)/carbonated hydroxyapatite composite applied as coating on ultra high molecular weight polyethylene

Poly(methyl methacrylate)/carbonated hydroxyapatite (PMMA/CHA) composite in the form of solution for its application as coating on ultra high molecular weight polyethylene (UHMWPE) substrate was studied. The coating has been prepared by mixing the carbonated hydroxyapatite in situ with the poly(methyl methacrylate) polymerization. The carbonated hydroxyapatite (CHA) was prepared by a conventional method. Fourier transformed infrared spectroscopy (FTIR) technique was used to study the hydroxyapatite synthesis and composite coating. The characterization of coating thickness was performed by light microscopy whereas the surface morphology was characterized by scanning electron microscopy (SEM) finding out a rough coating with a thickness of 29 μm. We have performed a pin-on-disk test to investigate the wear and friction behavior of the PMMA/CHA coating in dry conditions with loads ranging from 2 to 10 N; the same methodology was applied to test the UHMWPE substrates for comparatives studies. We also estimate the wear rate values of PMMA/CHA coating at each load, which are found to be ranging from k = 3.75 × 10⁻⁵ to 8.13 × 10⁻⁵ mm³/Nm. Additionally, the adhesion strength value between PMMA/CHA coating and UHMWPE substrate was 0.89 MPa.     

Preparation and characterization of processable electroactive polyaniline-polyvinyl alcohol composite

In this paper, the preparation and characterization of polyaniline-polyvinyl alcohol composites is described. The polyaniline composite was synthesized by chemical polymerization of aniline in media containing polyvinyl alcohol (10%, w/w). Oxidation of aniline results in a stable water based polyaniline dispersion, which can be cast to form a mechanically robust film.The electrical conductivity of the films increased with increasing amount of polyaniline to a high value of 2.5 S cm⁻¹. Cyclic voltammograms revealed that the composite materials are electroactive.     

Polyaniline for corrosion prevention of mild steel coupled with copper

Polyaniline emeraldine base/epoxy resin (EB/ER) coating was investigated for corrosion protection of mild steel coupled with copper in 3.5% NaCl solution. EB/ER coating with 5-10 wt% EB had long-term corrosion resistance on both uncoupled steel and copper due to the passivation effect of EB on the metal surfaces. During the 150 immersion days, the impedance at 0.1 Hz for the coating increased in the first 1-40 days and subsequently remained constant above 10⁹ Ω cm², whereas that for pure ER coating fell below 10⁶ Ω cm² after only 30 or 40 days. Immersion tests on coated steel-copper galvanic couple showed that EB/ER coating offered 100 times more protection than ER coating against steel dissolution and coating delamination on copper, which was mainly attributed to the passive metal oxide films formed by EB blocking both the anodic and cathodic reactions. Salt spray tests showed that 100 μm EB/ER coating protected steel-copper couple for at least 2000 h.     

Preparation and characterization of thermally stable epoxy-titanate coatings

Epoxy-polyamide coatings are used to protect metallic substrates in corrosive atmosphere. Thermal stability of the coating can be improved by the addition of inorganic cross-linking agent. Epoxy resin is incorporated with small percentage of silicone resin and cured with two types of hardeners such as polyamide and butyl titanate. The physical properties, heat resistance properties and electrochemical impedance behaviour of these coatings on steel in 0.5 M NaCl solution have been studied. The result implies that the heat resistant character of the titanate-cured coating is increased from 260 to 370 °C. The impedance study has shown that the coating resistance exerted by both the systems is in the range of 10⁵ Ω cm² after 6 days of immersion in 0.5 M NaCl. FTIR and Raman spectroscopy analysis confirm the presence of titanate linkage in the cured polymer coating. Thermal stability data indicate that the epoxy silicone resin cured with titanate hardener possesses higher thermal stability than that cured by polyamide hardener.     

The reaction of polyaniline with iodine

Polyaniline (PANI) (emeraldine) base has been exposed to iodine in an ethanol-water suspension. The conductivity of PANI increased from 10⁻⁹ S cm⁻¹ to 10⁻⁴ S cm⁻¹ already at the molar ratio [I₂]/[PANI] = 1, and a higher content of iodine had only a marginal effect. This is the result of the protonation of PANI base with hydriodic acid, which is a by-product of the oxidation of the emeraldine form of PANI to pernigraniline constitutional units. The reaction is discussed on the basis of FTIR spectra. An alternative reaction, a ring-iodination of PANI, is marginal. Only one iodine atom substitutes a hydrogen atom in about 12 aniline units, even at high iodine concentration, [I₂]/[PANI] = 8. The film of polyaniline base can be used in sensing iodine; after exposure to the iodine vapor, the conductivity of the polyaniline film increased.     

Impedance evaluation of permeability and corrosion of Al-2024 aluminum alloy coated with a chromate free primer

The corrosion of AA-2024 aluminum alloy protected with a chromate free primer is investigated after immersion in a 0.5 M NaCl aqueous solution. The water uptake by the coating increases continuously when the film, applied on an aluminum AA-2024 substrate, is placed in the 0.5 M NaCl solution. This increase is attributed to corrosion reactions taking place at the alloy/coating interface when water molecules reach the interface. The maximum water volume fraction absorbed by a similar coating applied on platinum substrate is 3.5 vol% and the permeability is 7.6 × 10⁻¹² m² s⁻¹. After 72 h immersion in the 0.5 M NaCl solution, the Nyquist representation of impedance data shows transmission line behavior that can be assigned to percolation pathway along the filler particles after water uptake. Charge transfer and diffusion of corrosion reactants and products occur, but no delamination was observed for immersion longer than 172 h. Furthermore, the coating resistance is still close to 10⁸ Ω cm⁻² after this immersion time. This accounts for the good protective performance of the coating.     

The oxidation of aniline with silver nitrate to polyaniline-silver composites

Silver nitrate oxidizes aniline in the solutions of nitric acid to conducting nanofibrillar polyaniline. Nanofibres of 10-20 nm thickness are assembled to brushes. Nanotubes, having cavities of various diameters, and nanorods have also been present in the oxidation products, as well as other morphologies. Metallic silver is obtained as nanoparticles of ∼50 nm size accompanying macroscopic silver flakes. The reaction in 0.4 M nitric acid is slow and takes several weeks to reach 10-15% yield. It is faster in 1 M nitric acid; a high yield, 89% of theory, has been found after two weeks oxidation of 0.8 M aniline. The emeraldine structure of polyaniline has been confirmed by FTIR and UV-vis spectra. The resulting polyaniline-silver composites contain 50-80 wt.% of silver, close to the theoretical expectation of 68.9 wt.% of silver. The highest conductivity was 2250 S cm⁻¹. The yield of a composite is lower when the reaction is carried out in dark, the effect of daylight being less pronounced at higher concentrations of reactants.     

3D porous polymeric conductive material prepared using LbL deposition

In this work a 3D porous polymeric conducting material is derived from a multi-percolated polymer blend system. The work has focused on the preparation of low surface area porous substrates from polymer blends followed by the deposition of polyaniline conductive polymer (PANI) on the internal porous surface using a layer-by-layer (LbL) technique. The approach reported here allows for the percolation threshold concentration of polyaniline conductive polymer (PANI) to be reduced to values of no more than 0.19%. Furthermore, depending on the amount of PANI deposited, the conductivity of the porous substrate can be controlled from 10⁻¹⁵ S cm⁻¹ to 10⁻³ S cm⁻¹.Ternary and quaternary multi-percolated systems comprised of high-density polyethylene (HDPE), polystyrene (PS), poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF) are prepared by melt mixing and subsequently annealed in order to obtain large interconnected phases. Selective extraction of PS, PMMA and PVDF result in a fully interconnected porous HDPE substrate of ultra-low surface area and highly uniform sized channels. This provides an ideal substrate for subsequent polyaniline (PANI) addition. Using a layer-by-layer (LbL) approach, alternating poly(styrene sulfonate) (PSS)/PANI layers are deposited on the internal surface of the 3-dimensional porous polymer substrate. The PANI and sodium poly(styrene sulfonate) (PSS) both adopt an inter-diffused network conformation on the surface. The sequential deposition of PSS and PANI has been studied in detail and the mass deposition profile demonstrates oscillatory behavior following a zigzag-type pattern. The presence of salt in the deposition solution results in a more uniform deposition and more thickly deposited PSS/PANI layers. The conductivity of these samples was measured and the conductivity can be controlled from 10⁻¹⁵ S cm⁻¹ to 10⁻⁵ S cm⁻¹ depending on the number of deposited layers. In the case of a porous sample which can be crushed, applying a load to the substrate can be used as an additional control parameter. In that sample a high load results in higher conductivity with values as high as 10⁻³ S cm⁻¹ obtained. The work described above has focused on very low surface area porous substrates in order to generate a conductive device with the lowest possible concentration values of polyaniline, but high surface area substrates can also be readily prepared using this approach.     

Electrochemical behaviour of an AISI 304L stainless steel implanted with nitrogen

In this paper the electrochemical behaviour of AISI 304L stainless steel implanted with nitrogen is studied in alkaline media and chloride-containing media, and it is compared with the behaviour of the unimplanted material. Implantation was done at a saturation dose (4 × 10¹⁷ ions cm⁻²) at an acceleration voltage of 150 keV. The results show a clear improvement of the corrosion resistance for the implanted specimens. No pitting potential is observed in the alkaline media or in the neutral media containing high chloride concentration. The improved corrosion resistance is presumed to be due to the modifications that N⁺ implantation induces in the passive layer that is naturally formed on the alloy. XPS analysis reveals Ni⁰ and Cr³⁺ enrichment in this passive layer. Moreover, a carbon-rich layer is found at the outermost part of the passive layer. The presence of this outermost layer is verified with electrochemical impedance measurements and SEM observations.     

Synthesis,characterization and corrosion protective properties of boron-modified polyurethane from natural polyol

A novel attempt has been made to incorporate boron in the backbone of castor oil to develop boron-modified polyester (BCPE) and polyurethane (BPU). The overall reaction strategy involved “single pot multiple reactions” in minimum solvent achieving about 50% reduction in the use of volatile organic compounds (VOCs) during the synthetic procedure. Spectral (I.R., ¹H NMR and ¹³C NMR), physicochemical and thermal (TGA and DSC) analyses of BCPE and BPU were carried out by standard methods. The physico-mechanical and corrosion/chemical resistance performances (in various corrosive media) tests of BPU coatings were also conducted to evaluate their coating properties. These studies revealed that (i) the incorporation of boron has a significant influence on structural and physico-chemical aspects, thermal stability as well as on coating properties of BPUs, (ii) interestingly, BPUs showed very good performance in alkaline media (unaffected in 5 wt% NaOH for 50 h) as compared to their other previously reported oil-based counterparts, (iii) boron, here, acts both as a modifier and crosslinker and (iv) BPUs serve as novel and promising candidates for use as corrosion protective coating material, which can be safely employed up to 220 °C.     

Mesoporous polyaniline or polypyrrole/anatase TiO2 nanocomposite as anode materials for lithium-ion batteries

A functional composite as anode materials for lithium-ion batteries, which contains highly dispersed TiO₂ nanocrystals in polyaniline matrix and well-defined mesopores, is fabricated by employing a novel one-step approach. The as-prepared mesoporous polyaniline/anatase TiO₂ nanocomposite has a high specific surface area of 224 m² g⁻¹ and a predominant pore size of 3.6 nm. The electrochemical performance of the as-prepared composite as anode material is investigated by cyclic voltammograms and galvanostatic method. The results demonstrate that the polyaniline/anatase nanocomposite provides larger initial discharge capacity of 233 mAh g⁻¹ and good cycle stability at the high current density of 2000 mA g⁻¹. After 70th cycles, the discharge capacity is maintained at 140 mAh g⁻¹. The excellent electrochemical performance of the polyaniline/TiO₂ nanocomposite is mainly attributed to its special structure. Furthermore, it is accessible to extend the novel strategy to other polymer/TiO₂ composites, and the mesoporous polypyrrole/anatase TiO₂ is also successfully fabricated.     

Synthesis and evaluating corrosion protection effects of emeraldine base PAni/clay nanocomposite as a barrier pigment in zinc-rich ethyl silicate primer

In the present work, polyaniline/clay nanocomposite (PAniCN) was synthesized by chemical oxidative polymerization of aniline monomers in the presence of Closite30B powders. XRD and SEM examinations were used to examine the intercalation and morphologies of PAniCN, respectively. Electrical conductivity test showed that the conductivity of final PAniCN was higher than pristine PAni by one order of magnitude. Synthesized nanocomposite was added to the zinc rich ethyl silicate primer to modify its barrier properties. The corrosion protection performances of modified and unmodified primers were evaluated using open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) in 3.5% sodium chloride solution for a period of 120 days. It was found that the modified primer had higher barrier properties than original primer. After 120 days of immersion, resistance of modified and unmodified primers reaches 5.565 × 10³ Ω cm² and 6.056 × 10² Ω cm² respectively. The OCP of both primers were lower than −800 mV/SCE during the immersion. Besides, the OCP of modified primer was higher than the original primer due to the passivation and barrier effects of PAniCN. Results revealed that the performance of modified primer improved strongly.