The use of polyindole for mild steel protection

Synthesis of polyindole was achieved on mild steel electrode previously coated with a very thin polypyrrole layer (PPy). Cyclic voltammetry technique was used for both syntheses; oxalic acid solution was used for synthesis of primer PPy coating and polyindole film (PI) was obtained from LiClO₄ containing acetonitrile medium. The corrosion performance of this PPy/PI coating was investigated properly in 3.5% NaCl solution by using anodic polarization and open circuit potential (E_ocp)–time curves and electrochemical impedance spectroscopy (EIS). This coating exhibited excellent barrier efficiency for a long time (about 190 h) and it was also able to provide a certain anodic protection. After 240 h of immersion time in corrosive test solution, the protection efficiency value was determined to be 98.9%.     

Nanograin magnetoresistive manganite coatings for EMI shielding against directed energy pulses

Two magnetoresistive manganites, La_0.83Sr_0.17MnO₃ and La_0.7Sr_0.3MnO₃, are synthesized by the environmentally friendly “deposition by aqueous acetate solution (DAAS)” technique. The manganite film has a grain size of 100 nm, and can be processed as thinly as 0.03 μm per layer, while the powder form has a crystallite size of 40 nm. These magnetoresistive materials are shown to be effective and inexpensive electromagnetic interference (EMI) shield for the extremely low frequency (ELF) EM fields. The electrical resistance of manganites is very sensitive to external influences, such as temperature and electromagnetic fields. Both permeability (μ) and conductivity (σ) of manganites tend to increase with increasing applied magnetic field. The manganites have been shown to “react” to field increases in a way that is particularly useful for shielding EMI field fluctuations (e.g., due to current or voltage spikes).

The manganite properties, e.g., crystal structure, film morphology, radiation absorption and reflection, electrical resistivity, and magnetization, etc., have been measured. The ceramic manganites have a metal–insulator transition at 300 K or higher, and are suitable for a room temperature operation. A thin film (approx. 0.1 μm) of La_0.83Sr_0.17MnO₃ was fabricated on a quartz tube or refractory ceramic fiber blanket. Using this thin manganite film, the EMI shielding effectiveness for the measured E-field attenuation is similar to that of a 25 μm thickness of copper tube, aluminum foil, and silver–nickel particle-dispersed paper. The silver–nickel impregnated paper has an EMI shielding effectiveness of 35 dB at 10 kHz, and 15 dB at 60 Hz (or frequency above 1 MHz). The ceramic manganites are chemically inert, thermally stable, and mechanically flexible. They provide low cost EMI shielding against directed energy pulses and may serve as a “signature reduction” barrier.     

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.     

Corrosion studies on electrochemically deposited PANI and PANI/epoxy coatings on mild steel in acid sulfate solution

The corrosion behavior of mild steel and mild steel covered by electrochemically deposited (a) polyaniline (PANI) film, (b) epoxy coating and (c) PANI/epoxy coating system in 0.1 M sulfuric acid solution were investigated by electrochemical impedance spectroscopy (EIS). Electrochemical deposition of PANI film was performed from aqueous solution of 0.5 M sodium benzoate and 0.1 M aniline at constant current density of 1.5 mA cm⁻². Epoxy coatings on mild steel and mild steel modified by PANI film were deposited at constant voltage. It was shown that thin PANI film had provided good corrosion protection of mild steel in 0.1 M sulfuric acid solution, and could be used for modification of mild steel prior to epoxy coating deposition. The increased corrosion protection of mild steel by PANI/epoxy coating system in the same solution was obtained.     

Corrosion resistance properties of Ormosil coatings on 2024-T3 aluminum alloy

The corrosion resistance behavior of organically modified silane (Ormosil) thin films on 2024-T3 aluminum alloy substrates was investigated using electrochemical impedance spectroscopy (EIS) and accelerated salt spray analysis techniques. Coatings were prepared containing 0–16.6 vol.% alkyl-modified silane, X_n---Si(OR)_4−n, where X=methyl, dimethyl, n-propyl, n-butyl, i-butyl, n-hexyl, n-octyl, or i-octyl. Coating thicknesses were measured to be in the 6–16 μm range, with the thickest coatings being observed for the highest concentrations of alkyl-modified silane. Contact angle measurements showed an enhancement in hydrophobicity of the Ormosil film imparted by increasing size and concentration of the alkyl-modifiers in the coating. In general, corrosion resistance characteristics, as determined using EIS and salt spray techniques, were found to increase with increasing alkyl-modified silane concentration and alkyl chain length. The best overall corrosion resistance was observed for coating systems containing ≥10.4 vol.% alkyl-modified silane; the hexyl-modified films exhibited corrosion resistance properties superior to the other Ormosil coatings. Immersion studies conducted in 0.5 M K₂SO₄ indicated that coating degradation occurs via hydration of the dense linear chain silicate network leading to the formation of porous cyclic structures.     

Hydrodechlorination of chloroorganic compounds in ground water by palladium catalysts: Part 1. Development of polymer-based catalysts and membrane reactor tests

A polymer-based catalytic membrane reactor was developed and applied for hydrodechlorination of chlorobenzene as a model compound of ground and waste water contaminants. The catalytically active membrane consists of a non-porous, thin film (about 3–7 μm) of poly(dimethylsiloxane) (PDMS) loaded with nano-sized Pd clusters. They were built-in either directly or as nano-sized, supported catalysts. A composite membrane, consisting of porous poly(acrylonitrile) (PAN) support and a Pd-loaded thin PDMS film, was fabricated on a coating machine. Defect-free membrane envelopes of 0.1 m² were produced and fitted into a membrane test cell. Gaseous hydrogen as reductant for hydrodechlorination is fed from the membrane’s back side directly to the catalyst, embedded in the PDMS layer. The chemical reactions at the Pd surface are accompanied by absorption of chlorobenzene from the water phase into the PDMS layer and desorption of benzene and HCl back to the water phase. The specific activity of supported catalysts decreased only slightly by PDMS incorporation, e.g., from 31 l/g(Pd) min for Pd/Fe on titania to 16 l/g(Pd) min for the same catalyst built-in a 7 μm thick supported PDMS membrane and measured in the membrane test cell. Directly built-in Pd clusters are less active and more difficult to prepare on a larger scale. Some catalyst deactivation was observed and may be balanced by development of more suited nano-sized supported catalysts.     

Thickness effects on structures and electrical properties of lead zirconate titanate thick films

PbZr_0.52Ti_0.48O₃ thick films with thickness of 1–6 μm have been prepared by a polymer-assisted MOD process. The polymer, poly(vinyl acetate) (PVAc) was introduced into PZT precursor solutions. The grain size increased from 30 nm to 100 nm with an increase of the additive amount of PVAc. Meanwhile, the grains grew larger (in a range of 100–500 nm) and the surface of the films became rougher with increasing film thickness. This promotes the structural relaxation and prevents cracking formation. The critical thickness at which the film begins to crack increases significantly. The dielectric constant and remanent polarization (P_r) increased from 1070 to 1490 and from 36.1 μC/cm² to 52.4 μC/cm², respectively, and the coercive field (E_c) decreased from 57.3 kV/cm to 41.3 kV/cm as the film thickness increased from 0.95 μm to 6.02 μm. PZT thick films prepared in this study are promising materials for MEMS applications.     

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.     

Fracture toughness of interfaces between glassy polymers in a trilayer geometry

We studied the fracture behavior of trilayer A/B/A assemblies based on polystyrene (PS) and poly(methylmethacrylate) (PMMA) where the central layer of the A polymer was confined (0.5–200 μm) between two thick plates of the B polymer (1– 3 mm). Diblock and random P(S-MMA) copolymers were used to provide a good stress transfer across the interfaces. Fracture experiments were performed with the double-cantilever beam method and the fracture mechanisms were observed by optical microscopy on microtomed slices of the damaged zone. The measured _c of the A/B interface fractured during the test was dependent on the molecular structure at the interface (random copolymer, diblock copolymer or no copolymer), on the crazing stress of the bulk materials and on the interfacial shear stresses. When the phase angle of the loading was even slightly positive, oblique crazes were observed in the PS increasing greatly _c. If PS was the central layer, this resulted in a very marked dependence of _c on the thickness of the central layer for a thickness range 10–200 μm which was not observed when the PMMA was the central layer. Thermal treatments modifying the interfacial shear stresses were also found to have a very strong effect on _c.     

Zinc deposited polymer coatings for copper protection

Polypyrrole (PPy) and polyaniline (PAni) coatings were electrosynthesized on copper, by using cyclic voltammetry technique. Then, these coatings were modified with the deposition of zinc particles from aqueous zinc sulphate solution. The electrodeposition of zinc was achieved at a constant potential value of −1.20 V, in the amount of ∼0.75 mg/cm². The corrosion performance of zinc modified polymer coatings were investigated in 3.5% NaCl solution; by using the electrochemical impedance spectroscopy (EIS), and anodic polarization curves. The zinc particles improved the barrier property of polymer films, thanks to formation of voluminous zinc corrosion products within the pores of polymer coating. Also, the zinc particles provided cathodic protection to the substrate, where the polymer film played the role of conductance between zinc particles and copper.     

Copper/polypyrrole multilayer coating for 7075 aluminum alloy protection

The corrosion behavior of 7075 aluminum (Al), copper modified Al (Al/Cu), polypyrrole modified Al (Al/PPy) and copper (under layer)/polypyrrole (top layer) modified Al (Al/Cu/PPy) samples were investigated in 3.5% NaCl solution. The copper plating on aluminum was carried out from acidic copper sulphate solution by electroless method. Polypyrrole (PPy) was electrochemically synthesized on Al and Al/Cu electrodes from 0.1 M pyrrole containing 0.4 M oxalic acid solution using cyclic voltammetry technique. The films synthesized were characterized by Fourier transform infrared spectroscopy (FT-IR). The thermal stability of PPy films was investigated by thermogravimetric analysis (TGA). The surface morphologies were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The corrosion behavior of samples was investigated by electrochemical impedance spectroscopy (EIS) and anodic polarization curves. The data obtained showed that the synthesis of PPy on top of the Cu layer significantly enhances the corrosion resistance of Al by exhibiting a barrier effect against the attack of corrosive environment.     

Using a new approach to analyze a depth profile of double bond conversion in model formulations

A new approach of analyzing the depth profile of double bond conversion as a function of film depth has been studied. By using a combination of statistical calculation and traditional FTIR, a new approach to analyze the depth profile of conversion “layer by layer” in the characterization of photopolymerization was explored. Utilizing a formula (X₁ + X₂ +  + X_n)/n = average conversion, n = 1, 2, 3, n is a number of layers (μm), an average conversion of any 5 μm depth could be calculated from the prior 5 μm conversion and the total average conversion. More detailed information of photopolymerization, such as the depth profile of conversion and a difference in conversion between the top 5 μm and the bottom 5 μm in a 25 μm film as a function of film depth, was obtained. This investigation was accomplished using a variation of film depth, non-photo bleaching photo initiator [PhI] as well as the concentration of PhIs in the presence of air and in the absence of air. Results of analyzing double bond conversion between traditional FTIR and the new approach (statistical calculation/FTIR) were compared.     

Application and evaluation of environmentally compliant spray-coated ormosil films as corrosion resistant treatments for aluminum 2024-T3

An epoxide modified silicate sol–gel film spray coated on an aluminum alloy 2024-T3 coupon was demonstrated to provide exceptional barrier and corrosion protection when compared to chromate-based surface treatments. Surface characterization indicated that the applied film was 2.2 μm thick and crack free. Potentiodynamic evaluation revealed that the film provided a continuous barrier of protection over a broad potential range. Comparison with standard Alodine-1200 type surface treatment indicated several orders of magnitude improvement in barrier protection and enhanced protection under accelerated corrosion test.     

Complex anticorrosion coating for ZK30 magnesium alloy

This work aims at developing a new complex anticorrosion protection system for ZK30 magnesium alloy. This protective coating is based on an anodic oxide layer loaded with corrosion inhibitors in its pores, which is then sealed with a sol–gel hybrid polymer. The porous oxide layer is produced by spark anodizing. The sol–gel film shows good adhesion to the oxide layer as it penetrates through the pores of the anodized layer forming an additional transient oxide–sol–gel interlayer.The thickness of this complex protective coating is about 3.7–7.0 μm. A blank oxide–sol–gel coating system or one doped with Ce³⁺ ions proved to be effective corrosion protection for the magnesium alloy preventing corrosion attack after exposure for a relatively long duration in an aggressive NaCl solution.The structure and the thickness of the anodized layer and the sol–gel film were characterized by scanning electron microscopy (SEM). The corrosion behaviour of the ZK30 substrates pre-treated with the complex coating was tested by electrochemical impedance spectroscopy (EIS), scanning vibrating electrode technique (SVET), and scanning ion-selective electrode techniques (SIET).     

Cathodic electro-deposition of low-temperature curable water-soluble polyepoxide coatings

Epoxidised phenol-novolac (EPN) type of polyepoxide resin was used for developing water-soluble cathodically electro-depositable coatings which could be self-curable without using any external/additional cross-linking agent. The self-curing of cathodically deposited films could be effected at a low temperature of 80°C in 30 min, as compared to 150–170°C in 30 min practised presently in many commercial cathodic electro-deposition (CED) installations. In this work, effect of varying molar ratio of secondary amines such as diethanol amine (DEtOA) and diethyl amine to epoxidised phenol-novolac (EPN) on the solubility of EPN–secondary amine adducts prepared at 80, 60 and 30°C for varying reaction times was investigated. Self-curing characteristics of EPN–DEtOA (1:2 moles) adduct at 30–160°C were studied.

Kinetics of film growth during CED was investigated by using aqueous solutions of acetic acid neutralised EPN–DEtOA (1:2 moles) adduct. Variables for kinetic studies were deposition time (30–600 s), applied voltage (5–250 V) and solution concentration (1–20% (w/w)). By carrying out CED of polyepoxide films, values of electro-deposition (ED) characteristics found were: ED yield as 5.89 mg/cm², Coulombic yield as 19.78 mg/C and dry film thickness (DFT) as 52.12 μm. Plots of DFT vs. deposition time (t), DFT vs. t^1/2 and current density vs. field strength were drawn to calculate the values of Coulombic efficiency of the process and film conductivity. Cathodically electro-deposited films were finally characterised for physical properties, chemical resistance and corrosion protection.     

Multilayer photoactive nanocolloidal PPy:PSS as a novel substitute for Pt free counter electrode in DSSC

Water dispersible and highly processable, Polypyrrole (PPy) nanocolloidal particles were synthesized by chemical oxidation polymerization with 15 wt % of anionic polyelectrolyte poly(styrene sulfonate) (PSS) at 5°C has been reported in this work. This polymer composite (PPy:PSS) was competent with conventional Pt counter electrode (CE) when compared for dye sensitized solar cells (DSSCs). Morphological analysis revealed smooth and spherical shaped nanoparticles of PPy. Interaction between the SO₃H groups and Py units in PPy improved the thermal stability of PPy with higher doping levels of PSS. The nanocolloidal solution was spin coated at 4000 rpm. The layer by layer, self‐assembled multilayer thin films were used as CE in DSSCs. There was a linear dependence of DSSCs performance with film roughness for the self‐assembled multilayer PPy:PSS films. Single layer films showed better electrocatalytic behavior than multilayer films. All the PPy:PSS films had good electrochemical stability. The DSSC efficiency of 3.40% was observed for chemically oxidized PPy with 15 wt % PSS for single layer film, with a highest FF of 0.7154. The low cost, good performance, rapid and simple fabrication method of PPy:PSS composite modified CE could be a potential alternative for Pt in the DSSCs. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43114.     

Electrochemical synthesis: a novel technique for processing multi-functional coatings

Electrochemical synthesis is a powerful tool for surface modification, substrate cleaning and formulation of thin films and bulk materials. It is especially suited for surface modification of fibers, metals and films. In the past decade electrochemical method has become the preferred technique for in situ passivation, and coating of commodity metals such as aluminum, zinc, copper and steel.

We have successfully synthesized different kinds of conducting polymers, including polypyrrole (PPy)–polyaniline (PANi) composites. The processability and corrosion performance of PPy/PANi, composite coatings are significantly better than those for either PPy or PANi, coatings.

In this paper, we will discuss the use of electrochemical technique in the synthesis and characterization of multi-functional corrosion resistant conducting polymer coatings for aerospace and automotive applications.     

Improvement of polypyrrole films for corrosion protection of zinc-coated AZ91D alloy

To improve the protection against the corrosion of AZ91D magnesium alloy provided by conducting polypyrrole (PPy) films, optimization of the electrochemical synthesis of the PPy film was investigated. The bi-layered PPy film was prepared under constant current control, first in a sodium tartrate solution containing molybdate and second in a sodium dodecylsulfate (DS) solution (after the AZ91D alloy was covered by zinc electroplating). Corrosion testing of the zinc-coated AZ91D alloy covered with the PPy film was performed in 3.5% NaCl solution. The more protective PPy film doped with tartrate ions (PPy-Tart film) was formed by the lower current density (CD). Doping of molybdate ions (MoO₄²⁻) into the PPy-Tart film significantly improved its corrosion protection properties. When the PPy-Tart-MoO₄ layer was covered by an outer PPy layer doped with DS ions, the corrosion protection was further improved. The imposition of ultrasonic waves during the electropolymerization of the inner PPy-Tart-MoO₄ layer was effective in the improvement of corrosion protection. The bi-layered PPy-Tart-MoO₄/PPy-DS film prepared under ultrasonic irradiation maintained the zinc-coated AZ91D alloy in the passive state during the corrosion test in NaCl solution for 221 h, during which no corrosion products appeared.     

Corrosion protection of copper by polyaminophenol films

The anticorrosion behaviour of polyaminophenol (PAP) films has been investigated in aqueous 0.5 M NaCl solution using electrochemical impedance spectroscopy and weight loss measurements. The effect of triazole compounds on the protection behaviour of the polymer was also examined. The polymer is obtained by in situ electropolymerization of 2-aminophenol monomer in alkaline hydroalcoholic solution. The results show that the polymer film reduces the corrosion of copper and that the electropolymerization in the presence of the azole compounds further increases the protective character of the coating. The polymer copper/solution interface is well described by an electrical equivalent circuit reflecting the behaviour typical of a porous film.     

Corrosion protection of iron by polystyrenesulfonate-doped polypyrrole films

Electropolymerized polypyrrole (PPy) has been studied as a protective coating for iron in NaCl 3% corrosive medium. The protection mechanism is of the galvanic type, and the main cause for the loss of protection is the progressive invasion of the film by chloride anions. To reduce exchanges between PPy counter-ions and chloride anions, a composite polyanions/PPy film was used. Polystyrenesulfonate was chosen as a large size counter-ion which could be trapped in the polymer matrix. Due to the negligible mobility of these anions, the film permselectivity changed from anionic to cationic. A significant improvement in PPy film protection efficiency was obtained.