Victoria J. Gelling

Conducting polymers for corrosion protection: a review

Conducting polymers (CPs) such as polyaniline (PANI), polypyrrole (PPy), and polythiophene (PTh) are used for the corrosion protection of metals and metal alloys. Several groups have reported diverse views about the corrosion protection by CPs and hence various mechanisms have been suggested to explain anticorrosion properties of CPs. These include anodic protection, controlled inhibitor release as well as barrier protection mechanisms. Different approaches have been developed for the use of CPs in protective coatings (dopants, composites, blends). A judicious choice of synthesis parameters leads to an improvement in the anticorrosion properties of the coatings prepared by CPs for metals and their alloys. This article is prepared as a review of the application of CPs for corrosion protection of metal alloys.

A Scanning Vibrating Electrode Study of Chromated‐Epoxy Primer on Steel and Aluminum

Chromated-epoxy primers are often used for corrosion control of iron and aluminum structural alloys. However, due to environmental concerns and adverse health effects surrounding such use of chromates, there is an intensive effort to find suitable repl acements for chromate-based coatings. This effort is hampered by lack of a detailed understanding of how the chromate-based coatings function. In this work, the scanning vibrating electrode technique (SVET), also known as the current density probe, was used to measure current flowing at chromated-epoxy coated steel and aluminum substrates. The coatings were scribed to simulate a defect through the coating to the metal substrate surface. A plain (nonchromated) epoxy coating was also studied for comparison . The SVET was used to map the current flowing in and around the defect while the sample was immersed in either 3% NaCl (steel) or in dilute Harrison solution (aluminum). Both steel and aluminum substrates coated with the chromated epoxy exhibited a significant delay before the onset of corrosion within the scribe, compared with substrates coated with nonchromated epoxy. Furthermore, the current density maps for steel suggest that the reduction reaction may occur at the surface of the chromated-epoxy coating. With the nonchromated-epoxy coating, the reduction reaction was always confined to the defect area.

Conducting Polymers and Corrosion III. A Scanning Vibrating Electrode Study of Poly(3‐octyl pyrrole) on Steel and Aluminum

Electroactive conducting polymers (ECPs) continue to be of considerable interest as components of corrosion-resistant coating s ystems. ECPs, in addition to being conductive, are redox active materials, typically with potentials that are positive of iron and a luminum. Thus, as with chromate, interesting and potentially beneficial interactions of ECPs with active metal alloys such as steel and aluminum are anticipated. In this work, the scanning vibrating electrode technique (SVET), also known as the current density probe, was used to probe such interactions between a poly(3-octyl pyrrole) coating (POP) and cold-rolled steel and aluminum (Al 2024-T3) substrates. The POP coatings were scribed to simulate a defect through the coating to the metal substrate surface. The SVET was used to map the current flowing in and around the defect while the sample was immersed in either 3% NaCl (steel) or in dilute Harrison solution (aluminum), an aqueous solution consisting of 0.35% (NH 4)2SO4, 0.05% NaCl. Although there were significant differences in the behavior of the POP-coated steel and POP-coated aluminum substrates, both exhibited a significant delay before the onset of any observable current compared to uncoated or epoxy-coated samples. Current density maps for the ste el clearly indicate that the reduction reaction occurred on the conducting polymer surface, with oxidation confined to the defect. Current density maps for the aluminum alloy never displayed significant oxidation at the defect. Rather, reduction (after a signifi cant delay) occurred at the defect as well as across the polymer surface, with concomitant localized undercoating oxidation of the al uminum substrate.

Novel Synthesis of Stable Polypyrrole Nanospheres Using Ozone

In this study, a novel and exceedingly simple method for the aqueous synthesis of stable, unagglomerated polypyrrole nanospheres was investigated. The method is template- and surfactant-free and uses only pyrrole monomer, water, and ozone. When the monomer concentration, exposure time to ozone, and temperature were varied, it was determined that the temperature was the critical factor controlling the particle size through particle size measurements via dynamic light scattering and transmission electron microscopy (TEM). From the particle size measurements, a particle size distribution with a number-weighted mean diameter of 73 nm and a standard deviation of 18 nm was achieved. The particles were also investigated using ζ-potential measurements, ultraviolet-visible (UV-vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis in an effort to determine the identity of the nanoparticles as well as the mechanism by which the nanoparticles are formed and stabilized.

In situ preparation and characterization of a conductive and magnetic nanocomposite of polypyrrole and copper hydroxychloride

A nanocomposite of conductive polypyrrole and ferrimagnetic copper hydroxychloride (Cu2Cl(OH)3) was prepared in a single-step via in situ chemical oxidation of pyrrole using CuCl2 as an oxidizing agent. In this study, it was shown that by monitoring the reaction time and conditions, the physical and chemical properties of polypyrrole and Cu2Cl(OH)3 in the nanocomposite can be easily controlled. This resulted in a nanocomposite with optimized conductivity and magnetic properties for a wide variety of applications such as magnetic recording, electromagnetic shielding, sensors, and spintronic devices. The obtained conductivity (0.0006–33 S cm−1) and magnetization (10.25–53.39 emu mol−1) measurements of the nanocomposite were within the range suitable for these applications and were achieved by controlling the reaction conditions and thus the composition of the nanocomposite. With FTIR, XPS and UV-Vis spectroscopy, it was observed that as the reaction proceeds with time under controlled conditions, the oxidation of pyrrole in the presence of CuCl2 leads to significant structural changes in polypyrrole as well as gradual precipitation of Cu2Cl(OH)3. XRD and SEM analysis showed the effect of reaction conditions on the crystallinity and the morphology of the polypyrrole/Cu2Cl(OH)3 nanocomposite. While the chemical and structural variations in polypyrrole were correlated with the conductivity of the nanocomposite, measured via the conductive-AFM technique, the changes in magnetic properties of the nanocomposite were mainly attributed to the variations observed in the crystallinity of Cu2Cl(OH)3.

Tungstate and vanadate-doped polypyrrole/aluminum flake composite coatings for the corrosion protection of aluminum 2024-T3

Polypyrrole (PPy) doped with either tungstate or vanadate as counter anions was synthesized by chemical oxidative polymerization on the surface of aluminum (Al) flakes. This resulted in the deposition of PPy on the surface of the Al flakes leading to the formation of doped PPy/Al flake composite pigments. These composite pigments were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, conductive-atomic force microscopy, four-point probe conductivity, and X-ray photoelectron spectroscopy. Furthermore, these composites were incorporated in an epoxy-amide binder system in order to formulate a primer for an aluminum 2024-T3 substrate. The coatings were exposed to the Prohesion test conditions and corrosion resistance properties were monitored by electrochemical impedance spectroscopy, DC polarization, galvanic coupling, and scanning electrochemical microscopy measurements. It was found that the doped PPy/Al flake coatings provided sacrificial protection to the underlying aluminum 2024-T3 substrate. Additionally, the release of dopants from PPy backbone resulted in the passivation in the defect areas improving the corrosion protection ability.

Synthesis and Characterization of Micaceous Iron Oxide/Polypyrrole Composite Pigments and Their Application for Corrosion Protection of Cold-Rolled Steel

Novel hybrid composite pigments consisting of micaceous iron oxide (MIOX) and polypyrrole (PPy) were synthesized using a chemical oxidative polymerization method and water as a reaction medium. Three different particle sizes (5, 10, and 30 μm) of MIOX, namely, MIOX5, MIOX10, and MIOX30, were used for the synthesis of MIOX/PPy composite pigments. The synthesized hybrid composite pigment was characterized by scanning electron microscopy (SEM) for morphology, energy-dispersive spectroscopy (EDS) for elemental analysis, four-point probe conductivity, and conductive-atomic force microscopy (C-AFM) for conductivity studies. Density tests were also performed for the adhesion between MIOX and PPy. MIOX30/ PPy composite pigment-based coatings were formulated at 15, 25, and 35% pigment volume concentration (PVC) on cold-rolled steel and were exposed to salt spray test conditions according to ASTM B117. Corrosion performance was analyzed by electrochemical impedance spectroscopy (EIS) and anodic polarization. Equiva...

Two-Electrode Electrochemical Impedance Sensor: Part 1—Response to Coating Degradation on Conductive Substrates

Abstract Electrochemical impedance spectroscopy (EIS) is widely used for understanding and quantifying the corrosion protective quality of coatings. However, the traditional single-cell EIS (SCEIS) configuration has largely been limited to laboratory testing on small panels partly due to the requirement of an electrical connection to the substrate, which implies damage to the protective coating. We have studied a two-cell EIS (TCEIS) configuration that increases the flexibility of EIS, enabling its use in the field testing of coatings without the need to damage the coating to achieve an electrical connection to the substrate. Comparison measurements between the SCEIS and the TCEIS were carried out with coated panels under three different accelerated weathering protocols (ultraviolet [UV], salt spray, and alternating UV/salt spray). Measurements from the TCEIS and the SCEIS showed similar impedance spectral changes with exposure time under the first two exposure protocols but had significant measurement de...

Two-Electrode Electrochemical Impedance Sensor: Part 2—Impedance Measurement and Simulation of Coatings on Nonmetal Substrates

Abstract Electrochemical impedance spectroscopy (EIS) has been studied extensively as a quantitative technique for evaluating protective coatings, which degrade unavoidably, regardless of their sub...

Development of chromate-free coated steel sheet with high corrosion resistance and conductivity

The ideal coating structure, which can achieve both high corrosion resistance and high conductivity, was examined by SEM analysis of conventional chromate-free coated steel sheets. Based on the results of SEM analysis, it was found that high conductivity was achieved by maintaining the convex parts of zinc plating crystals at the coating surface. High corrosion resistance was also achieved by combining a novel silicate binder and metal salt. The results of electrochemical analysis revealed that the silicate binder contributed to suppressing the anodic reaction, while a composite coating involving epoxy resin and phosphoric acid was effective for suppressing the cathodic reaction and maintaining a high barrier property for an extended time.