Corrosion protection of steel by bi-layered polypyrrole doped with molybdophosphate and naphthalenedisulfonate anions

Bi-layered polypyrrole (PPy) coating was investigated for corrosion prevention of steels. The PPy coating consisted of the inner layer doped with PMo₁₂ (PMo₁₂) and ions and the outer layer doped with naphthalenedisulfonate (NDS) ions. PMo₁₂ ions doped in the inner layer make the passive oxide film on steel stabilized and the outer layer doped with large organic ions of NDS restricts decomposition and release of PMo₁₂ ions in the inner layer. Corrosion tests were made in 3.5% NaCl aqueous solution for the steels covered by the single PPy-PMo₁₂, single PPy-NDS, and bi-layered PPy-PMo₁₂/PPy-NDS coatings. The single PPy-PMo₁₂ and PPy-NDS coatings maintained the steel in passive state for 34 h and 24 h, respectively. The bi-layered coating kept the steel in passive state and prevented corrosion of the steels for the longer time period.     

Corrosion protection with polyaniline and polypyrrole as anticorrosive additives for epoxy paint

Accelerated immersion tests have been carried out in the laboratory to investigate the performance of polyaniline emeraldine salt and polypyrrole composite with carbon black as additives of an epoxy paint coating. The steel panels coated with paint modified with polyaniline emeraldine salt presented the best protection after 720 h of exposure in 3.5% NaCl solution. The results indicated that this conducting polymer might works as both corrosion inhibitor and adhesion promoter. The protective mechanism imparted by conducting polymers is also discussed.     

Corrosion protection properties of lacquer coatings on steel modified by carbon black nanoparticles in NaCl solution

Nanometer carbon black (CB) grafted with polyvinyl alcohol was obtained by surface modification, and its size was about 60 nm. In the ultrasonic field, the composite lacquer coatings with different contents of CB nanoparticles were prepared by mechanical agitation. Electrochemical impedance spectroscopy (EIS), anodic polarization curves, immersion measurements and salt fog tests were used to evaluate the corrosion performances of the composite coatings applied on steel in NaCl solution. It was observed that composites coatings with 1 wt% CB nanoparticles reduced drastically the corrosion rate of steel.     

Corrosion protection of iron by polypyrrole modified by copper using the cementation process

Polypyrrole (PPy) coatings have been deposited on iron from aqueous oxalic acid solution at different current densities. The polymer deposit obtained at a current density of 2 mA cm⁻² yields strongly adherent and smooth PPy layers. The modification of the film by incorporation of copper microparticles using the cementation process was applied. The resulting PPy/Cu film electrodes were characterized by scanning electron microscopy and EDX analysis. The protective performance against corrosion of these films is evaluated by using open circuit potential monitoring in highly corrosive solution (3% NaCl + HCl, pH 1). The results obtained were promising in the protection against corrosion.     

Influence of iron microstructure on the performance of polyacrylic acid as corrosion inhibitor in sulfuric acid solution

The corrosion inhibition behavior of bulk nanocrystalline ingot iron (BNII) fabricated from coarse polycrystalline ingot iron (CPII) by severe rolling technique by polyacrylic acid (PAA) was studied in 0.1 M H₂SO₄ using electrochemical impedance spectroscopy and potentiodynamic polarization techniques. The results indicated that PAA inhibited the acid induced corrosion of both iron specimens, with greater effect noted for BNII. The corrosion inhibiting effect was influenced by the microstructure of the iron samples. Synergistic inhibition effect was observed on addition of iodide ions to PAA in case of CPII while for BNII inhibition efficiency marginally increased.     

Corrosion inhibitors for iron in hydrochloride acid solution by newly synthesised pyridazine derivatives

Inhibition by some newly synthesised pyridazine compounds of corrosion of pure iron in 1 M HCl solution has been studied using weight loss measurements, polarisation and impedance spectroscopy methods. The inhibiting action is more pronounced with stet-5-benzyl-6-methylpyridazin-3-yl thioethanoic (P1) and (5-benzyl-6-methylpyridazin-3-yl) ethyl thioethanoate (P3) and their inhibition efficiency increases with concentration to attain the maximum value of 85% and 81% at the 10⁻⁴ M, respectively. We note good agreement between gravimetric and electrochemical methods (potentiodynamic polarisation and impedance spectroscopy (EIS)). Polarisation measurements show also that the pyridazines act essentially as cathodic inhibitors. The cathodic curves indicate that the reduction of proton at the pure iron surface happens with an activating mechanism. The presence of the sulphur atom increases the inhibition efficiency changing the adsorption mechanism.     

Corrosion protection of cold-rolled steel by zinc-rich epoxy paint coatings loaded with nano-size alumina supported polypyrrole

High porosity and intense galvanic function related low electrolytic barrier profile and fast delamination of zinc-rich paints (ZRPs) are addressed by the utilisation of intimately structured, highly dispersed, polypyrrole (PPy) deposited alumina particles (PDAPs) embedded zinc-rich hybrid paints. The more globular but less-packed structure type PPy-contained water-solvent-prepared PDAPs-composited hybrids comprising spherical zinc pigment at 70 wt.%, provided moderate galvanic function with enhanced electrolytic barrier properties. In addition, the less globular structured but well-packed PPy-comprised aqueous ethanol-solvent-prepared PDAPs-composited hybrid coatings indicated highly efficient suppressed galvanic function and improved barrier properties, realising solid performance improvement over conventional ZRPs in immersion and salt-spray chamber tests. Furthermore, the application of highly dispersed PDAPs at a content of 3.2 wt.% while PPy incorporated into zinc-rich hybrids at 0.16 wt.% is proposed to result in emerging additional functionalities increasing long-term anticorrosive performance of ZRPs by inhibiting sacrificial and self-corrosion of zinc and scavenging oxidative radicals thereby hindering oxidative degradation of the organic binder.     

The corrosion protection of mild steel by polypyrrole/polyphenol multilayer coating

Electrochemical synthesis of very thin polyphenol (PPhe) film was achieved on polypyrrole coated mild steel electrode (MS/PPy) and a multilayer coating was obtained, cyclic voltammetry technique was used for the synthesis. The corrosion performance of this multilayer coating and single PPy coating were investigated in 0.05 M H₂SO₄ solution by using electrochemical impedance spectroscopy (EIS), anodic polarization curves and open circuit potential (E_ocp)-time curves were used. It was found that the multilayer coating could provide much better protection than the single PPy coating for corrosion of MS for much longer periods and an efficiency of 98.3% was determined for this coating after 340 h exposure time in corrosive medium. It is proposed that the very thin PPhe film coated on top of PPy coating lowered the porosity and improved the barrier effect of the coating significantly.     

Corrosion protection of aluminum pigments by sol-gel coatings

New sol-gel coatings for the corrosion protection of aluminum pigments were developed. To this end, the pigment particles are first coated with a silica layer by phosphoric acid-catalyzed sol-gel processing of Si(OEt)₄, to which either hexadecyltrimethoxysilane or dimethyldimethoxysilane is condensed. The coated pigments have excellent anticorrosive properties in alkaline solutions as well as under boiling water conditions.     

Morphology and properties of polypyrrole electrosynthesized onto iron from a surfactant solution

The morphology of polypyrrole (PPy) deposits during electrosynthesis onto iron electrodes in sodium bis(2-ethylhexyl) sulfosuccinate (AOT) solutions have been investigated using Scanning Electron Microscopy (SEM). At the early stages of electrosynthesis, fibrillar, toroidal and globular forms are observed while polymerization at longer times leads to a closely packed deposit. The effects of electropolymerization parameters on the obtained morphology are discussed. It is proposed that electropolymerization rate and polymer stiffness are important factors in controlling the morphology. Electrochemical investigations demonstrate that toroid-shaped deposits present electrochemical activity. The experimental results indicate that a gelatinous product, formed as a result of iron dissolution, grows simultaneously with PPy.     

Effects of grain size on the electrochemical corrosion behaviour of electrodeposited nanocrystalline Fe coatings in alkaline solution

Effect of grain size reduction on the electrochemical corrosion behaviour of nanocrystalline Fe was investigated using Tafel polarization curves and electrochemical impedance spectroscopy (EIS) measurements. Nanocrystalline iron was fabricated by pulse electrodeposition using citric acid bath. The grain size of a nanocrystalline surface was analyzed by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The corrosion resistance of Fe in alkaline solution considerably increased as the grain size decreased from microcrystalline to nanocrystalline. The behaviour of passive film growth and corrosion was discussed in terms of excess of free energy caused by nanocrystalline surface.     

Corrosion inhibition of Armco iron by 2-mercaptobenzimidazole in sodium chloride 3% media

The effect of 2-mercaptobenzimidazole (2MBI) on the corrosion of Armco iron in NaCl media has been investigated in relation to the concentration of the inhibitor by various corrosion monitoring techniques. Surface morphology was studied by scanning electron microscopy (SEM). Results obtained revealed that 2MBI is a good anodic inhibitor. The addition of increasing concentrations of 2MBI moves the corrosion potential towards positive values and reduces the corrosion rate. EIS results show that the changes in the impedance parameters (R_t and C_dl) with concentrations of 2MBI is indicative of the adsorption of these molecules leading to the formation of a protective layer on iron surface. The adsorption of this compound is also found to obey Langmuir’s adsorption isotherm in NaCl.     

Enhanced corrosion protection of MgO coatings on magnesium alloy deposited by an anodic electrodeposition process

MgO coatings were prepared on magnesium alloy surface by an anodic electrodeposition process in concentrated KOH solution followed by heat treatment in air. The phase composition and microstructure of the as-formed MgO coatings were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The corrosion behavior of the MgO-coated samples was evaluated by electrochemical measurements and immersion tests in Hanks’ solution. The results showed that the MgO-coated Mg alloy exhibited a much superior stability and lower corrosion rate, and thus enabled to improve the corrosion resistance, whereas the bare Mg alloy suffered from severely localized corrosion attack.     

Corrosion of iron in highly acidic hydro-organic solutions

In acidic water-organic solvents of ethylene glycol (EGOH), propylene glycol (PGOH), methanol (MeOH) and ethanol (EtOH), iron corrosion was studied by monitoring the corrosion potential, the potentiodynamic polarization curves and electrochemical impedance diagrams. In these aqueous glycols and alcoholic solutions containing HCl having concentrations of 0.5 up to 9 M, it has been shown by electrochemical analysis (I-E curves) that dissolution mechanism of iron is similar to that one in pure acidic aqueous solutions if only we take into account the relative amount of water in the medium. Based in our experimental data, water has an important role in the transfer kinetics of protons to the metallic electrode and limits electro dissolution rate of iron. When water quantity is sufficient at the metal surface, the acidity is a governing factor in the evolution of corrosion process.     

Raman spectroscopy analysis of polypyrrole films as protective coatings on iron

In situ Raman spectroscopy was used to study the redox modifications of electropolymerized polypyrrole (Ppy) films used as protective coatings on iron. A preliminary study of the redox behavior of Ppy on platinum was carried out for highlighting the most sensitive bands to potential variations: the 1560–1620 cm⁻¹ as well as the 930 and 980 cm⁻¹ peaks show a strong dependence on the applied potential. In situ Raman spectra of Ppy on iron were recorded at different times after immersion in a 3% NaCl solution. They formally display the same peaks as those found for platinum, allowing to characterize the redox state of the Ppy film at the solution/film interface. Additional ex situ Raman spectra allowed to identify the corrosion products at the Ppy/metal interface. These results complement kinetics analysis early developed to understand the protection mechanism and its loss.     

Electrochemical study of corrosion inhibition and adsorption behaviour for pure iron by polyacrylamide in H2SO4: Synergistic effect of iodide ions

Corrosion inhibition and adsorption behaviour for pure iron in 0.5 M H₂SO₄ by polyacrylamide (PA) were investigated using electrochemical techniques. The effect of iodide ion additives was also studied. It was found that inhibition efficiency increased with PA concentration. Corrosion inhibition was afforded by adsorption of PA onto the metal following El-Awady kinetic-thermodynamic adsorption isotherm model via chemisorption mechanism. A mixed inhibition mechanism is proposed for the inhibitive effects of PA as revealed by potentiodynamic polarization technique. A synergistic effect was observed between PA and KI as evident from the values of synergism parameter found to be greater than unity.     

Electrochemical synthesis of polypyrrole films on copper from phytic solution for corrosion protection

Phytic acid (C₆H₁₈O₂₄P₆), the principal phosphorous storage form in many plant tissues, is a green material. A polypyrrole (PPy) doped with phytic acid (IP₆) was electrosynthesised on copper from an aqueous phytic acid solution. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and SEM were used to characterise the polymer. The polymer-covered copper was subjected to a corrosion test in NaCl solution. The dissolution of copper covered with PPy-IP₆ was found to be greatly inhibited in NaCl solution. The inhibition indicated protection of the PPy-IP₆ layer against copper corrosion.     

Initial corrosion protection of Zn–Mn alloys electrodeposited from alkaline solution

The effects of a deposition current density (c.d.) on the corrosion behaviour of Zn–Mn alloy coatings, deposited from alkaline pyrophosphate solution, were investigated by atomic absorption spectrophotometry (AAS), X-ray diffraction (XRD), atomic force microscopy (AFM), optical microscopy, electrochemical impedance spectroscopy (EIS) and measurement of corrosion potential (E_corr). XRD analysis disclosed that zinc hydroxide chloride was the main corrosion product on Zn–Mn coatings immersed in 0.5 mol dm⁻³ NaCl solution. EIS investigations revealed that less porous protective layer was produced on the alloy coating deposited at c.d. of 30 mA cm⁻² as compared to that deposited at 80 mA cm⁻².     

A study on mechanism of corrosion protection of polyaniline coating and its failure

Polyaniline (PANI) coatings were electrochemically deposited on substrates of stainless steel and platinum in solutions of 0.2 M H₂SO₄ and 0.1 M aniline by cyclic voltammetry. The corrosion protection of the PANI coatings and their failure were investigated in 0.2 M H₂SO₄ solution. It was observed that the corrosion protection ability of the coating to steel substrate was increased with the increase of the coating thickness. The corrosion protection ability was mainly attributed to the passivating effect of PANI due to its oxidizing ability in its emeraldine state. During its operation, the PANI coating in emeraldine state tended to gradually lose its corrosion protection ability. This gradual failure of the PANI coating, but faster than expected, was confirmed to be related to a gradual reduction of the emeraldine PANI and a gradually increased resistance between the PANI coating and the stainless steel substrate. These findings lead to a new mechanism for the corrosion protection of PANI coating and its failure.     

Synergistic corrosion inhibition study of Armco iron in sodium chloride by piperidin-1-yl-phosphonic acid-Zn system

Electrochemical techniques, weight loss method and surface analysis were used to study the synergistic inhibition offered by Zn²⁺ and piperidin-1-yl-phosphonic acid (PPA) to the corrosion of Armco iron in 3% chloride solution. It is observed that the combination between PPA and Zn²⁺ shows excellent inhibition efficiency. The potentiodynamic polarization curves reveal that 5 × 10⁻³ mol l⁻¹ of PPA has only 76.7% inhibition efficiency whereas the mixture containing 5 × 10⁻³ mol l⁻¹ PPA -20%Zn²⁺ has 90.2% inhibition efficiency. This suggests that a synergistic effect exists between Zn²⁺ and PPA. The Fourier transform infrared (FTIR) spectrum of the film formed on iron indicates phosphonates zinc salt formation. A suitable mechanism of corrosion inhibition is proposed based on the results obtained. The surface film analysis showed that in the absence of Zn²⁺, the protective film consists of Fe²⁺-PPA complex formed on the anodic sites of the metal surface, whereas in the presence of Zn²⁺, the protective film consists of Fe²⁺-PPA complex and Zn(OH)₂.