Effect of surface treatment of pigment particles with polypyrrole and polyaniline phosphate on their corrosion inhibiting properties in organic coatings

The effect of pigment particle surface treatment with conductive polymers on the corrosion inhibiting properties of organic paints was investigated. Mixed oxides possessing the spinel and perovskite structures were synthesised for the study. Natural graphite and pigments based on ferric oxide and silicate were studied. Coating materials based on a water-based epoxy resin were prepared for the investigation of the corrosion protection properties of the pigments, the surfaces of which had been provided with a conductive polymer layer. Laboratory corrosion tests were applied to the paint films. A commercial corrosion protection pigment, based on modified zinc phosphate, served as the corrosion protection efficiency standard. Polyaniline phosphate was found preferable to polypyrrole as the modifying agent of the pigment surface regarding the pigment's corrosion inhibiting efficiency. Surface treatment with the conductive polymers is also beneficial to the mechanical properties of the paint.     

Corrosion inhibition of steel using mesoporous silica nanocontainers incorporated in the polypyrrole

Mesoporous silica nanocontainer powders were applied as corrosion inhibitor hosts. These powders were dispersed in the polypyrrole matrix by electropolymerization technique. The protection properties of these composite coatings with and without inhibitor were studied in 2 g dm⁻³ chloride ion solutions at constant pH. Open circuit potential (OCP), inductive coupled plasma (ICP), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and Fourier transform infrared spectroscopy (FTIR) results showed that the substrates were protected due to the release of corrosion inhibitor from mesoporous silica in the chloride media compared to the coatings without corrosion inhibitor. The released corrosion inhibitor reacted with substrate and made a protective phase during corrosion. This phase can heal the corroded area as a self-healing compound.     

Poly(m-phenylendiamine-co-o-aminophenol) coatings on mild steel: Effect of comonomers feed ratio on surface and corrosion protection aspects

Copolymer of m-phenylendiamine (mPD) and o-aminophenol (oAP) has been electrochemically deposited on mild steel from an aqueous solution of oxalic acid using cyclic voltammetric technique. The copolymer structure was confirmed by Proton Nuclear Magnetic Resonance (¹H NMR) and Attenuated Total Reflection Infrared (ATR-IR) spectroscopic techniques. Surface characterisation results indicated that the formed copolymer coatings posses uniform, smooth surface and strong adherence towards the metal surface. Corrosion performance of copolymer coatings was investigated in 0.5 M HCl solution using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) methods. Results showed that corrosion performance of copolymer coatings depends on the feed ratio of both the monomer units in copolymer chain. It was found that the copolymer feed ratio of mPD:oAP = 70/30 in coatings exhibited the highest performance due to its superior surface nature than other copolymer coatings.     

The corrosion protection of mild steel by single layered polypyrrole and multilayered polypyrrole/poly(5-amino-1-naphthol) coatings

Electrochemical synthesis of polypyrrole (PPy) and top coat of poly(5-amino-1-naphthol) (PANAP) on PPy films from oxalic acid solution was achieved on mild steel (MS) by cyclic voltammetry technique. The morphology and the structure of the films were investigated by scanning electron microscopy (SEM). The corrosion performance of this multilayer coating and single PPy coating were investigated in 3.5% NaCl solution by using open circuit potential (E_ocp)–time curves, polarization curves and electrochemical impedance spectroscopy (EIS). It was found that the multilayer PPy/PANAP coating could provide much better protection than single PPy coating for corrosion of MS. It was observed that corrosion performance of coatings was increasing with immersion period. This was explained by auto-undoping properties of PPy coatings during immersion in corrosive solution. The improved corrosion performance in the presence of PANAP top coat on PPy was explained by increase in barrier effect of bilayer films.     

Influence of the doping agent on the corrosion protection properties of polypyrrole grown on aluminium alloy 2024-T3

The corrosion protection properties of polypyrrole (PPy) electrodeposited onto aluminium alloy 2024-T3 substrates were investigated as a function of the doping agent. We used camphor sulfonic acid (CSA), para toluene sulfonic acid (p-TSA), phenylphosphonic acid (PPA), oxalic acid (OA) and cerium nitrate salt (Ce(NO₃)₃) as doping agents. The resulting coatings have been evaluated towards corrosion protection of aluminium alloy 2024-T3 using electrochemical impedance spectroscopy (EIS). Complementary, scanning electron microscopy (SEM) provided images on the morphology and the thickness of the coatings. The results showed that coatings formed using Ce(NO₃)₃ solution protect the substrate more efficiently compared to the other coatings.     

Smart corrosion sensing phenanthroline modified alkyd coatings

Alkyd resin was chemically modified with 1,10-phenanthroline-5-amine and characterized by Fourier transform infrared (FTIR) and ¹³C Nuclear magnetic resonance (¹³C NMR) spectroscopy. The complex forming ability of phenanthroline modified alkyd resin with Fe²⁺ ions was studied by UV–Visible spectroscopy. Mixture of Fe²⁺ solution and modified alkyd resin showed new absorption bands in UV–Visible spectroscopy confirmed the formation of modified alkyd resin-Fe(II) complex. Corrosion sensing property of modified alkyd coating was evaluated by immersing the coated mild steel specimens in 3.5% NaCl solution. Color change was observed in the coating due to onset of corrosion at metal-coating interface. Electrochemical impedance spectroscopy (EIS) was used for correlating the polarization resistance (R_p) of coating with color change. Scanning electron microscopic (SEM) analysis on the surface of metal specimens indicated that the point of color change was the corrosion site. Results revealed that phenanthroline modified alkyd resin can be used in corrosion sensing coating formulations.     

Electrodeposition of homogeneous and adherent polypyrrole on copper for corrosion protection

Electrochemical synthesis of polypyrrole (PPy) on copper electrodes is researched using different techniques. The synthesised films are found to be very adherent and homogeneous. The corrosion behaviour of Cu/PPy is assessed in a 3.5% NaCl solution using polarisation curves and open circuit potential-time. The relationship between porosity and anticorrosive properties is demonstrated. The chronopotentiometry technique is seen to be the best to produce a good coating that yields good protection against copper corrosion for long immersion times.     

Electrodeposition of polypyrrole–titanate nanotube composites coatings and their corrosion resistance

Polypyrrole (PPy) films (2 μm) containing titanate nanotubes (TiNT) were deposited from 0.5 mol dm⁻³ pyrrole (Py) and 1 g dm⁻³ of TiNT in 0.1 mol dm⁻³ aqueous oxalic acid on 904 L stainless steel (SS) 0.1 mm thickness at 298 K. Electron microscopy showed that the nanotubes were adsorbed on the PPy surface and uniformly dispersed in the polymer matrix. The PPy/TiNT composite contained <10 wt.% titanates which showed an increase of 53% hardness compared with polypyrrole alone. The TiNT provide nucleation centres to catalyze the polymerization of pyrrole and can adsorb up to 240 mg g⁻¹ of the monomer. The corrosion rates for SS, SS/PPy and SS/PPy/TiTN composites, evaluated by linear sweep voltammetry and open-circuit potential measurements in 3% w/v NaCl, were 1.61, 0.008 and 0.004 mg dm⁻² day⁻¹, respectively, indicating that corrosion rates of stainless steel decreased by up to three orders of magnitude in the presence of the composite films.     

High performance corrosion protective DGEBA/polypyrrole composite coatings

Conducting polymers (CP) have been envisaged as nontoxic substitutes for chromates in corrosion protective coatings owing to their environmental stability, excellent corrosion resistant performances and good adhesion to metal substrate. Recent advancements in the field of corrosion protective coatings have therefore headed towards the utilization of conducting polymers as “smart corrosion inhibitors” in the formulation of eco-friendly anti-corrosive coatings. With the aim to develop a facile method for the synthesis of anti corrosive coating material having superior corrosion protective properties, the present work reports the corrosion studies of polypyrrole/DGEBA composite coatings on mild steel (MS). The coatings were characterized by physicochemical as well as physicomechanical studies while the corrosion protective performance was evaluated by chemical resistance in different corrosive media, corrosion rate and open circuit potential (OCP) measurements. The morphologies of corroded, coated, uncorroded and uncoated samples were investigated by SEM studies. The composite coatings were found to show far superior anti corrosive performance than PANI/epoxy coatings in acid, alkaline as well as saline environments.     

Influence of inhibitor addition on the corrosion protection performance of sol–gel coatings on AA2024

Sol–gel films are actively investigated during the last decade as possible candidates for environmentally friendly pre-treatments. However, the important drawback in this case is the lack of active corrosion protection and self-healing ability.     

The electrochemical synthesis of polypyrrole at a copper electrode: corrosion protection properties

Pyrrole was successfully electropolymerized at a copper electrode in a near neutral sodium oxalate solution to generate a homogeneous and adherent polypyrrole film. The growth of these films was facilitated by the initial oxidation of the copper electrode in the oxalate solution to generate a copper oxalate pseudo-passive layer. This layer was sufficiently protective to inhibit further dissolution of the copper electrode and sufficiently conductive to enable the electropolymerization of pyrrole at the interface, and the generation of an adherent polypyrrole film. These films remained stable and conducting for periods exceeding eight days and exhibited significant corrosion protection properties in acidified and neutral 0.1 mol dm⁻³ NaCl solutions even on polarization to high anodic potentials.     

Study on corrosion resistance and roughness of micro-plasma oxidation ceramic coatings on Ti alloy by EIS technique

Micro-plasma oxidation (MPO) technique has been developed quickly in recent years. The produced ceramic coatings are reported to possess fine properties and promising application prospects in many fields. The aim of this work is to study the corrosion resistance and the roughness of the micro-plasma oxidation ceramic coatings on Ti alloy by electrochemical impedance spectroscopy (EIS) technique. Compound ceramic coatings were prepared on Ti-6Al-4V alloy by pulsed bi-polar micro-plasma oxidation in NaAlO₂ solution. The phase composition and element distribution in the coating were investigated by X-ray diffractometry and electron probe micro-analyzer. EIS of the coatings was measured through CHI604 electrochemical analyzer in 3.5% NaCl solution. The ceramic coating is composed of a large amount of Al₂TiO₅ and a little α-Al₂O₃ and rutile TiO₂. The coating is of double-layer structure with the loose outer layer and the dense inner layer. The thickness of the coatings is reduced when the working frequency or the cathode pulse current density is increased, while the thickness is increased when the frequency or the anode current density is increased. The established “equivalent circuit” of the coatings is consistent with the double-layer structure. The electric charge transfer resistance (R_t) in the equivalent circuit can be used to assess the corrosion resistance of the coatings, which is consistent with the result of the polarizing curves test. And the empirical exponent (n₁) of the constant phase element (Q₁) in the equivalent circuit can be used to assess the surface roughness of the coatings, which is consistent with the surface SEM analysis of the coatings.     

Effect of benzotriazole (BTA) addition on Polypyrrole film formation on copper and its corrosion protection

Benzotriazole (BTA) was added in a conducting Polypyrrole (PPy) film prepared on copper in oxalic acid aqueous solution containing pyrrole monomer to improve corrosion protection by the PPy film and reduce copper corrosion. When BTA was added in the preparation solution, the copper surface was covered by a BTA–Cu complex layer before the anodic polymerization of PPy was started. On the copper surface with the BTA layer, the initial dissolution of copper was inhibited and the PPy polymerization-deposition was started immediately after the anodic current was imposed. The PPy film thus formed was doped with oxalic ions and ionized BTA and was homogeneous in thickness and strongly adhesive. The PPy film containing BTA protected the copper from corrosion in 3.5 wt.% NaCl solution. In 400 h of immersion, copper dissolution was inhibited with 80% protection efficiency relative to that of bare copper.     

Characterisation and corrosion protection properties of polypyrrole electropolymerised onto aluminium in the presence of molybdate and nitrate

This paper describes the first attempts for the electrosynthesis of polypyrrole films containing molybdate onto aluminium electrodes. Electrogeneration was carried out in an alkaline solution in the presence of molybdate, nitrate and the monomer. The optimum concentrations for electropolymerisation were chosen in order to improve the corrosion protection of the substrate. The coatings were characterised by SEM/EDX and IR spectroscopy and the cyclic voltammetric response of the film is discussed. Pitting corrosion resistance was studied by means of open circuit potential and potentiodynamic measurements. The results presented below show that molybdate remains entrapped into the polymer matrix, providing greater resistance to breakdown of passivity in chloride media.     

Effect of dopant on the corrosion protective performance of environmentally benign nanostructured conducting composite coatings

The present work study reports the comparative corrosion protective performance of nanostructured methyl orange (MO) doped polyaniline (PANI) and camphorsulphonic acid (CSA) doped poly(1-naphthylamine) (PNA) dispersed polyurethane-based composite coatings against mild steel (MS). The influence of the dopant on the passivation of metal was analyzed using two different dopants. The nanostructure of the conducting polymers—MO-PANI and CSA-PNA was confirmed by transmission electron microscopy (TEM). The corrosion protective performance of the coatings against MS was evaluated by the physico-mechanical properties and corrosion rate measurements.     

Hydrodynamic effect on the behaviour of a corrosion inhibitor film: Characterization by electrochemical impedance spectroscopy

Influence of hydrodynamic conditions on the behaviour of an inhibitor film used in the high speed mechanical field is studied. Experimentations are realized with a Rotating Disk Electrode (RDE). Electrochemical Impedance Spectroscopy (EIS) is carried out at the corrosion potential and also at anodic and cathodic over voltages under various rotation rates and after different immersion times. EIS technique is used to determine the beneficial effect of hydrodynamic conditions on the film formation. This technique characterizes also inhibitive layer modifications for high electrode rotation speeds and after long immersion times. Different analyses, XPS and AFM, were carried out and have confirmed film structure evolution with flow conditions.     

Electrochemical synthesis of bilayer coatings of poly(N-methylaniline) and polypyrrole on mild steel and their corrosion protection performances

Homopolymer and bilayer coatings of poly(N-methylaniline) (PNMA) and polypyrrole-dodecylsulfate (PPy-DS) have been electropolymerized on a mild steel (MS) surface by the potentiodynamic method in aqueous oxalic acid solutions. In order to include dodecylsulfate ion as dopant in the polypyrrole, sodium dodecylsulfate was also added to the polymerization solution of pyrrole. Characterization of coatings was carried out by the cyclic voltammetry, Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy (FESEM). Corrosion behavior of the polymer coated MS electrodes was investigated in highly aggressive 0.5 M HCl solution by the Tafel test and electrochemical impedance spectroscopy (EIS) techniques. Corrosion test revealed that among the protective coatings obtained, the PNMA/PPy-DS bilayer exhibited the best corrosion resistance at all immersion times.     

Influence of pH on the synthesis and properties of polypyrrole on copper from phytic acid solution for corrosion protection

Polypyrrole (PPy) films were deposited on copper from “green” inhibitor of phytic acid solution for corrosion protection of copper. The corrosion protection property of the PPy layer was studied by an immersion test in a NaCl aqueous solution. The polymerization process of PPy on copper changed with the pH values of phytic acid solution and current density applied. When one oxidized bare copper in phytic acid solution at various pHs containing pyrrole monomer, a thin layer consisting of complex compound of Cu-phytate was firstly formed, followed by the formation of the PPy layer doped with phytate anion on the complex compound layer. The complex compound layer passivated the copper surface and its thickness increased with the lower pH value of the solution and the lower current density applied. It was found that the PPy coating prepared in the phytic acid solution at pH 4 exhibit the most protective property against copper corrosion.     

FP-based formulations as protective coatings in oil/gas pipelines

Corrosion in the interior of pipelines is a major and costly problem encountered in the oil and gas industry. In this context, a fluoropolymer and a hybrid epoxy/fluoropolymer resin were studied for their potential use to prevent corrosion. The fluoropolymer coating required the use of a primer layer. The coatings were formulated to maintain the excellent abrasion and chemical resistance properties of fluoropolymers, while enhancing adhesion to the substrates. Standard corrosion experiments, including chemical immersion, adhesion, and salt fog tests, were used for preliminary evaluation. Coatings were characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy before and after exposure to corrosive environments. Electrochemical properties were studied with electrochemical impedance spectroscopy, by monitoring the resistance and capacitance of the coatings over time. The results obtained in this work will fill a knowledge gap and will aid in the selection of the proper composition and thickness of anticorrosion coatings for use in a highly corrosive media.     

Effect of mixture ratio on water uptake and corrosion performance of silicone-epoxy hybrid coatings coated 2024 Al-alloy

A silicone-epoxy hybrid coating cured with amino silane was developed to provide corrosion protection on 2024 Al-alloy using air spraying. Water uptake characteristics of the silicone-epoxy hybrid coatings were investigated by electrochemical impedance spectroscopy in a 5 wt% NaCl solution. The effect of mixture ratio of silicone-epoxy and amino-silane on the water uptake (solubility, diffusion coefficient and permeation) was studied by using a single frequency (10 kHz) capacitance method. The glass transition temperature (T_g) was also investigated through differential scanning calorimeter (DSC) before and after immersion in the NaCl solution. Consequently, the excess of silicone-epoxy resin or amino silane improved the solubility of water in the coatings. A low water permeation coefficient was obtained with the mixing ratio 8/2 of silicone-epoxy and amino-silane, in which the T_g value was found to be larger than other three mixing ratios before immersion. After immersion for 750 h, the impedance modulus of EFA 2 coating (mixing ratio 8/2) in the low frequency was still close to 10⁸ Ω cm² that accounts for the good protective performance.