In situ investigation of corrosion localised at the buried interface between metal and conducting polymer based composite coatings

Conducting polymers are controversially discussed for application in corrosion protection. In our earlier work we presented a hypothesis for explaining why sometimes very good performance is observed and sometimes fast and disastrous coating break-down, especially in the presence of defects in the coating. By avoiding continuous macroscopic networks of conducting polymer in composite coatings the latter can be prevented, opening up the application of conducting polymers for secure performance in intelligent corrosion protection. In this paper we add further proof. However, at the interface between coating and metal, corrosion induced by galvanic coupling between conducting polymer and the metal still remains a problem, even in the absence of defects in the coating. Now we found that for some metals this corrosion at the buried interface can be studied in situ by Scanning Kelvin Probe microscopy, providing the means to better develop strategies for counter acting this problem.     

聚苯胺在金属防腐领域中的应用

聚苯胺是最有应用价值的导电高分子之一,综述了聚苯胺在金属防腐领域的最新应用,讨论了其相关的防腐机理,并对PAN i的未来进行了展望。聚苯胺的存在使得金属和聚苯胺膜界面处形成一层致密的金属氧化膜,使该金属的电极电位处于钝化区,而使金属得到保护。聚苯胺作为防腐涂层具有独特的抗划伤和抗点蚀性能,是一种具有广阔前景的并适合于严酷条件下的新型金属腐蚀涂料。     

Conducting polymers for corrosion protection: What makes the difference between failure and success?

The potential of conducting polymer coatings for corrosion protection is a topic of current controversy. In general, the efficacy of conducting polymers very much depends on how they are applied and on the conditions of the corrosion experiment, i.e. depending on the exact conditions a conducting polymer may have excellent protection capability or may lead to a disastrously enhanced corrosive attack. A number of possible protection mechanisms are proposed. The most interesting corrosion protection mechanism that is currently discussed for conducting polymer-based coatings is the intelligent release of inhibitor anions. However, in many cases this does not work in the presence of larger defects. Based on scanning Kelvin probe studies of artificial defect initiated reduction and delamination of polypyrrole films in nitrogen (reduction) or air (reduction and delamination) atmospheres it will be shown in this paper that this is due to a switching from mixed anion release and cation incorporation during reduction of the conducting polymer to an exclusive cation incorporation for reduction over extended length scales. Although only results for polypyrrole are discussed here, for fundamental reasons this is postulated to be of general validity for all conducting redox polymers such as polypyrrole, polyaniline, and polythiophene. Hence, all coatings based on pure conducting polymer layers or pigments with macroscopic percolation networks will fail in the presence of larger defects, even though they may show excellent corrosion protection for smaller ones.     

One-dimensional conducting polymer nanocomposites: Synthesis, properties and applications

Intrinsically conducting polymers have been studied extensively due to their intriguing electronic and redox properties and numerous potential applications in many fields since their discovery in 1970s. To improve and extend their functions, the fabrication of multi-functionalized conducting polymer nanocomposites has attracted a great deal of attention because of the emergence of nanotechnology. This article presents an overview of the synthesis of one-dimensional (1D) conducting polymer nanocomposites and their properties and applications. Nanocomposites consist of conducting polymers and one or more components, which can be carbon nanotubes, metals, oxide nanomaterials, chalcogenides, insulating or conducting polymers, biological materials, metal phthalocyanines and porphyrins, etc. The properties of 1D conducting polymer nanocomposites will be widely discussed. Special attention is paid to the difference in the properties between 1D conducting polymer nanocomposites and bulk conducting polymers. Applications of 1D conducting polymer nanocomposites described include electronic nanodevices, chemical and biological sensors, catalysis and electrocatalysis, energy, microwave absorption and electromagnetic interference (EMI) shielding, electrorheological (ER) fluids, and biomedicine. The advantages of 1D conducting polymer nanocomposites over the parent conducting polymers are highlighted. Combined with the intrinsic properties and synergistic effect of each component, it is anticipated that 1D conducting polymer nanocomposites will play an important role in various fields of nanotechnology.     

A review on conducting polymer coatings for corrosion protection

Corrosion of metals is one of the most important problems in the manufacturing industries. Many corrosion control methods use coatings of conducting polymers and conversion layers that contain toxic and environmentally hazardous materials, especially chromium compounds. These objectives have led to the development of new protective coating strategies that employs nanocomposites and carbon-based materials. In recent years, conducting polymers have attracted much attention because of their wide range of industrial applications and economic viability. Polymers possess long-chain carbon linkages and therefore, upon adsorption are able to block large areas of the corroding metal surfaces. The thin films adsorbed on the metal substrate provide a barrier effect between the metal and its environment. This review article summarizes the different techniques used in corrosion protection of metals, conducting polymers and nanomaterials, nanocomposites, and carbon-based materials in corrosion science.     

Undoped polyaniline–surfactant complex for corrosion prevention

Due to the strict regulations on the usage of heavy metals as the additives in the coating industries, the search for effective organic corrosion inhibitors in replacement of metal additives has become essential. Electrically conducting polymers have been shown to be effective for corrosion prevention, but the poor solubility of these intractable polymers has been a problem. We have explored a polyaniline–4-dodecylphenol complex (PANi–DDPh) to improve the dissolution, and it has been shown to be an effective organic corrosion inhibitor. With the surfactant, DDPh, PANi could be diluted into the coatings, and the properties of the coatings were affected. An emeraldine base (EB) form of PANi was also found to be oxidized by the hardener. The oxidized form of polyaniline provides improved corrosion protection of metals than that of emeraldine base since the value of the standard electrode potential for the oxidized form of PANi is higher than that of EB. Additionally, the surfactant improves the wet adhesion property between the coating and the metal surface. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2849–2856, 1999     

Anticorrosion efficiency of zinc-filled epoxy coatings containing conducting polymers and pigments

The dependence of the corrosion-inhibiting properties of zinc-filled organic coatings on the nature of the conducting polymers and conducting pigments added and on the pigment particles’ surface coating with conducting polymer layers were investigated. The following materials were selected to examine the corrosion-inhibiting properties of the conducting polymers: polyaniline phosphate (PANI), polypyrrole (PPy), natural graphite, and carbon nanotubes. Conducting pigment combinations for application in coating materials were formulated by applying pigment volume concentrations (PVC) of 0.3%, 0.5% and 1%, which were completed with Zn dust to obtain pigment volume concentrations/critical pigment volume concentrations (PVC/CPVC) = 0.64. Such conducting pigment/zinc dust combinations represented corrosion inhibitors to be used as ingredients in protective coatings. Solvent-based 2K epoxy resin based coating materials containing the corrosion inhibitors so formulated were prepared to examine their anticorrosion properties. The pigmented coatings were subjected to laboratory corrosion tests in simulated corrosion atmospheres and to standardized mechanical resistance tests. The protective coatings so obtained exhibited a higher efficiency than coating materials containing zinc dust alone. The coating material containing carbon nanotubes at PVC = 1% and the coating material containing graphite coated with polypyrrole (C/PPy) at PVC = 0.5% emerged as the best zinc-filled coating materials with respect to their corrosion-inhibiting efficiency. Treatment with the conducting polymers had a beneficial effect on the coating materials’ mechanical properties.     

Phosphonate-functionalized polyfluorene and its application in organic optoelectronic devices

Conjugated polar polymers, in which the conjugated backbones are chemically anchored with functional polar side groups, can be processed with water/alcohol solvents, and thus multilayered device architectures can be easily realized via sequential solution processing of the toluene-soluble emissive polymer and alcohol-soluble electron-transporting polymer without intermixing. Regarding their use in organic optoelectronic devices, the success in achieving efficient charge injection and intimate contact between metal electrodes and organic semiconductors is very vital for enhancing the device performance. In this short review, it gives a brief review to neutral alcohol-soluble phosphonate-functionalized polyfluorene, mainly concerning the electronic structure at the phosphonate-functionalized polyfluorene/aluminum cathode interface and its successful application in multilayered polymer optoelectronic devices including polymer light-emitting diodes and polymer solar cells.     

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.     

A new smart coating of polyaniline–SiO2 composite for protection of mild steel against corrosion in strong acidic medium

Organic coating approaches 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. The present work is directed towards the synthesis of polyaniline (PANI) and polyaniline–SiO₂ composites (PSCs) by chemical oxidation polymerization in the presence of phosphoric acid and evaluation of synthesized PANI and PSCs for protection of mild steel from corrosion in a strong aggressive medium (i.e. 1.0 mol L^–1 HCl). A suitable coating with PSC was formed on mild steel using epoxy resin by the powder coating technique. A comparative study of the corrosion protection efficiency of mild steel coated with PANI and PSC in 1.0 mol L^–1 HCl solution was evaluated using the Tafel extrapolation, chrono‐amperometry and weight loss methods. The PSC coating showed that a significant reduction in the corrosion current density reflects the better protection of mild steel in an acidic environment. Higher protection efficiency up to 99% was achieved by using PSC‐coated mild steel at 6.0 wt% loading of PSC in epoxy resin. The coating performance and corrosion rate of mild steel were investigated by using immersion of polymer‐coated mild steel in 1.0 mol L^–1 HCl for 60 days and indicated that PSC‐coated mild steel showed better performance from corrosion than PANI in an acidic medium.© 2012 Society of Chemical Industry     

导电高分子材料研究进展

综述导电高分子材料的发展及应用。介绍导电高分子材料的分类,复合型及结构型导电高分子材料的导电机理,以及它们在膜分离技术、微波焊接、防腐、电致变色器件等方面的应用。并指出了导电高分子材料目前的研究趋势。     

Contribution of acoustic emission technique for monitoring damage of rubber coating on metallic surfaces: Comparison with electrochemical measurements

Chlorobutyl coatings are industrially applied on metallic inner walls of HCl storage tanks, in order to protect steel against corrosion. Rubber coating constitutes an efficient barrier against HCl penetration up to metallic surface; yet, traces of monochlorobenzene (MCB) into HCl solutions can locally damage the coating and induce both acid infiltration and rapid corrosion of steel under the coating. Acoustic emission (AE) technique, due to its non-intrusive feature and its sensitivity, is a potential technique for the detection of polymer coating damage as well as metallic corrosion under the coating. In that context, this technique was coupled and compared to electrochemical measurements at least for metal damage evaluation. AE signals produced by corrosion of bare metal in HCl solution were first characterized, and then AE and electrochemical results obtained during metal and/or coating damage were compared, in the case of physical or chemical deteriorations of the coating, in an HCl solution containing traces of monochlorobenzene. In case of physical coating damaging, AE and polarisation resistance measurements are in good correlation as soon as metallic corrosion starts. When polymer coating suffers a solvent impregnation, previously to HCl solution contact, acoustic activity increases as soon as corrosion under the coating occurs, whereas polarisation resistance measurements do not allow detecting corrosion of steel.     

Bacterial exopolysaccharides for corrosion resistance on low carbon steel

Corrosion is a global issue that affects safety and economics. There is an increasing demand for bio‐based polymers for industrial applications and production of polymers by micro‐organisms is especially attractive. This work reports on the electrochemical and physical properties of exopolysaccharides produced from lactic acid bacteria and their suitability as anti‐corrosive coatings. Bacterial exopolysaccharide coatings protected low carbon steel from corrosion by reducing ionic diffusion rates and maintaining a relatively passive metal‐coating interface. The data suggest the kinetics of film deposition are fast (<5 min) and there is little excess (loosely bound) material when hydrated. Measurements show thin (50 nm) coatings that when exposed to water exhibit self‐repairing phenomenon. The corrosion protection offered by the coatings is reported as the corrosion rate calculated from the corrosion current obtained by electrochemical impedance and polarization spectroscopy. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45032.     

The search for enhanced dielectric strength of polymer-based dielectrics: A focused review on polymer nanocomposites

This report traces the leading scientific endeavors to enhance the dielectric strength of polymer dielectrics for energy storage and electrical insulation applications. Remarkable progress has occurred over the past 15 years through nanodielectric engineering involving inorganic nanofillers, coatings, and polymer matrices. This article highlights the challenges of dielectric polymers primarily toward capacitors and cable/wire insulation. It also summarizes several major technical approaches to enhance the dielectric strength of polymers and nanocomposites, including nanoparticle incorporation in polymers, filler-polymer interface engineering, and film surface coating. More attention is directed to interface contributions, including rational design of core-shell structures, use of low-dimensional fillers and thermally conducting fillers, and inorganic surface coating of polymer films. These efforts demonstrated the enhancement in dielectric strength by 40–160% when controlling the fillers below 5 wt% in polyvinylidenedifluoride (PVDF) composites. This article also discussed the possible dielectric mechanisms and the positive role of interfaces against charge transport traps for attaining higher breakdown strength. The investigation of low-dimensional filler/coating materials of high thermal conductivity can be key scientific subjects for future research.     

Electrochemical impedance behavior of graphite-dispersed electrically conducting acrylic coating on AZ31 magnesium alloy in 3.5 wt.% NaCl solution

The paper deals with understanding the electrochemical impedance behavior of (a) chromate coating (b) electrically conducting polymer coating and (c) polyurethane coating under different combinations applied over AZ31 magnesium alloy in an effort to develop a conducting organic coating that can offer corrosion protection as well as electrical conductivity. The study indicates that dispersion of graphite in acrylic coating though significantly brings down the electrical resistance; application of such a coating on the magnesium alloy does not offer good resistance against corrosion. In order to gain both the corrosion resistance as well as electrical conductivity an intermediate coating such as polyurethane needs to be provided. The paper discusses the electrochemical impedance behavior of the above coatings.     

Correlation of morphology and barrier properties of thin microwave plasma polymer films on metal substrate

The barrier properties of thin model organosilicon plasma polymers layers on iron are characterised by means of electrochemical impedance spectroscopy (EIS). Tailored thin plasma polymers of controlled morphology and chemical composition were deposited from a microwave discharge. By the analysis of the obtained impedance diagrams, the evolution of the water uptake ?, coating resistance and polymer capacitance with immersion time were monitored and the diffusion coefficients of the water through the films were calculated. The impedance data correlated well with the chemical structure and morphology of the plasma polymer films with a thickness of less than 100 nm. The composition of the films were determined by means of infrared reflection absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The morphology of the plasma polymer surface and the interface between the plasma polymer and the metal were characterised using atomic force microscopy (AFM). It could be shown that, at higher pressure, the film roughness increases which is probably due to the adsorption of plasma polymer nanoparticles formed in the plasma bulk and the faster film growth. This leads to voids with a size of a few tens of nanometers at the polymer/metal interface. The film roughness increases from the interface to the outer surface of the film. By lowering the pressure and thereby slowing the deposition rate, the plasma polymers perfectly imitate the substrate topography and lead to an excellent blocking of the metal surface. Moreover, the ratio of siloxane bonds to methyl-silyl groups increases which implies that the crosslink density is higher at lower deposition rate. The EIS data consistently showed higher coating resistance as well as lower interfacial capacitance values and a better stability over time for the film deposited at slower pressure. The diffusion coefficient of water in thin and ultra-thin plasma polymer films could be quantified for the smooth films. The measurements show that the quantitative evaluation of the electrochemical impedance data requires a detailed understanding of the film morphology and chemical composition. In addition, the measured diffusion coefficient of about 1.5×10⁻¹⁴ cm² s⁻¹ shows that plasma polymers can act as corrosion resistant barrier layers at polymer/metal interfaces.     

Development of novel conducting composites of linseed‐oil‐based poly(urethane amide) with nanostructured poly(1‐naphthylamine)

Novel conducting polymer composites of linseed‐oil‐based poly(urethane amide) (LPUA) were synthesized using nanostructured poly(1‐naphthylamine) (PNA). The combination of the electrically conducting PNA with LPUA was accomplished through different weight percent loadings (0.5–2.5 wt%) of the conducting polymer. The particle size of the nanocomposite was determined using transmission electron microscopy and was found to be in the range 17–27 nm. Intermolecular hydrogen bonding between the two polymers and formation of urea linkages were confirmed by Fourier transform infrared spectroscopy. The electrical conductivity of the nanostructured conducting composites at 2.5 wt% loading was found to be comparable to that reported for polyaniline (PANI)/polyurethane at 30 wt% loading of PANI. This shows the superior properties of PNA and its potential for application in anti‐static as well as corrosion‐protective coatings. The present method of formulation of composites using an oil‐based polymer matrix is useful and economically feasible in the sense that a great variety of oil‐based polymer matrices can be used to form composites that are ecologically safe and exhibit properties similar to commercial polymers. Copyright © 2007 Society of Chemical Industry     

THERMAL CONTACT CONDUCTANCE OF A COATED PAPER/METAL INTERFACE

A better understanding of the parameters associated with heating of the coated paper during drying process would permit a more accurate design and control of the process to achieve an improved coated paper quality and printability. Following the application of the coating, the coated paper passes through non-contact dryers (i.e. infrared dryers and impinging hot air dryers). When the coating has coalesced, further drying is achieved with steam-heated, contact dryers. One parameter affecting the heat transfer from a metallic dryer drum to the coated paper is the thermal contact conductance at the interface between the coated paper and the drum. In this paper, the thermal contact conductance of a coated paper/metal interface is determined and compared to that of the uncoated paper. Two types of base stock and one type of coating are considered. The thermal contact conductance values are given as a function of the applied interface pressure.     

THERMAL CONTACT CONDUCTANCE OF A COATED PAPER/METAL INTERFACE

A better understanding of the parameters associated with heating of the coated paper during drying process would permit a more accurate design and control of the process to achieve an improved coated paper quality and printability. Following the application of the coating, the coated paper passes through non-contact dryers (i.e. infrared dryers and impinging hot air dryers). When the coating has coalesced, further drying is achieved with steam-heated, contact dryers. One parameter affecting the heat transfer from a metallic dryer drum to the coated paper is the thermal contact conductance at the interface between the coated paper and the drum. In this paper, the thermal contact conductance of a coated paper/metal interface is determined and compared to that of the uncoated paper. Two types of base stock and one type of coating are considered. The thermal contact conductance values are given as a function of the applied interface pressure.     

Ultra thin layers as new concepts for corrosion inhibition and adhesion promotion

The adsorption and self-organization process as well as the surface reactions of several bifunctional adhesion promoters on different oxide surfaces have been investigated. The aim was to improve the adhesion between metal oxides and different organic coatings. We developed a large number of bifunctional compounds, which are able to adsorb spontaneously on different pre-treated metal (oxide) surfaces. The second group can be designed for grafting different otherwise incompatible layers.

Therefore, a special two-step procedure has been developed: (1) adsorption of the designed bifunctional molecules on the substrate and (2) surface reaction of the terminal reactive group with a polymeric top coating or with further monomers resulting in a strongly bond composite.

For this purpose substances were chosen having a surface reactive group, an aliphatic spacer and a reactive group for a suitable top layer. Phosphonic acids forming strong bonds with several metal surfaces were chosen as surface-active groups on metal oxide substrates.

The termination of these compounds with further reactive groups opened a wide range of possible applications. Functionalities like amino or carboxylic groups allowed reactions with commercial lacquers (e.g., polyurethane) for improving adhesion promotion and corrosion inhibition of the metal substrates. By using polymerizable groups like thiophene and pyrrole an in situ surface polymerization with further monomers is possible directly on the substrate.

The adsorbed films of bifunctional phosphonic acids on metal (oxide) substrates were characterized by contact angle measurements, X-ray photoelectron spectroscopy (XPS), the surface polymerized films were investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), cyclovoltammetry (CV), and electrochemical impedance spectroscopy (EIS). The results showed that monolayers were formed, which were correctly oriented on the surfaces: the phosphonic acid group was attached to the substrate whereas the terminal group was free standing for further reactions. Surface polymerization with additional monomer was possible either chemically or electrochemically resulting in smooth polymer layers of adjustable thickness. The conducting polymers were found to be p-conductive with a doping level of about 30%. Conductivity measurements revealed a conductivity of about 0.13 S/cm for the best films.

Based on this principle two possible applications are given: firstly, a corrosion protecting system for steel, and secondly, a model release system for protecting steel after damage of the coating.