Enhancing corrosion resistance of zinc-filled protective coatings using conductive polymers

Organic coatings containing zinc are amply used for the protection of metals, particularly steel structures. Ways to reduce the zinc content in the coating materials are sought for environmental and financial reasons. Our previous work (Kohl, Prog Org Coat 77:512–517, 2014; Kohl and Kalendová, Mater Sci Forum 818: 171–174, 2015a) suggested that one of the options consists in the use of conductive polymers in the formulation of the zinc coatings. The benefits of conductive polymers include nontoxicity, high stability, electric conductivity and redox potential. Previously we focussed on the effect of conductive polymers added to the organic coatings so as to complete the zinc volume concentration to 67%. The anticorrosion efficiency of the organic coatings was found to improve with increasing polyaniline phosphate or polypyrrole concentrations. Zinc content reduction in the system, however, did not attain more than 5%. The present work focusses on systems where the organic coatings are prepared with zinc having a pigment volume concentration PVC = 50%. Zinc content reduction in the system attains up to 20%. This work examines the mechanical and anticorrosion properties of the organic coatings with reduced zinc contents. The present work was devoted to the feasibility of using of conductive polymers in the formulation of coatings with reduced zinc contents. The conductive polymers included polyaniline, polypyrrole and poly(phenylenediamine); these were synthesised and characterised using physico-chemical methods. Polyphenylenediamine as a potential corrosion inhibitor has not been paid adequate attention so far. Subsequently, organic coatings with reduced zinc contents and containing the pigments at 0.5, 1 and 3% volume concentrations were formulated. The coatings were subjected to mechanical tests and accelerated corrosion tests to assess their mechanical and corrosion resistance. The corrosion resistance of the organic coatings was also studied by linear polarisation. The results of the mechanical tests, accelerated corrosion tests and linear polarisation measurements indicate that the organic coating properties get affected by the conductive polymer type as well as by the pigment volume concentration. The important finding is that the use of conductive polymers in coatings with reduced zinc contents was beneficial in all cases.     

Enhanced Anticorrosion Properties of Epoxy Coatings from Al and Zn Based Pigments

Anticorrosion epoxy coatings from Al and Zn based pigments were synthesized by adjusting their volume ratios, aiming at their increasing anticorrosion performances. The anticorrosion properties were examined via electrochemical impedance spectroscopy, Tafel polarization curve analysis and salt spray test. The coating morphologies before and after the salt spray tests were studied via scanning electron microscopy(SEM). The elemental and chemical compositions of the corroded surfaces of the coatings were analyzed by means of X-ray photoelectron spectroscopy(XPS). The results indicate that the coating composed of Al/Zn at 10:1(volume ratio) displays the maximum anticorrosion performances, which are superior to those of pristine Al or Zn based pigment.     

Potential of zinc based-graphene oxide composite coatings on mild steel in acidic solution

This study introduces varying concentrations of graphene oxide (GO) as a filler into zinc chromate in forming composite coatings to improve the corrosion protection of mild steel. The purity of synthesized GO was inferred through the application of complementary characterization techniques, including FT-IR, XRD, Raman, SEM-EDX, and TEM analyses. GO doped zinc chromate coatings were deposited on the surface of mild steel through the brushing method. Electrochemical studies, i.e., electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PD) were conducted to elucidate the anticorrosion properties of the coated mild steel exposed to 0.5 ​M HCl solution. It was revealed that the highest anticorrosion protection was attained at low doping amount of 0.5% of GO with a corrosion rate of 0.036 mpy. Surface analyses revealed that incorporating GO into zinc chromate coating can effectively improve the anticorrosion properties and adhesion strength.     

Influence of organic corrosion inhibitors on the corrosion performance of organic–inorganic hybrid coatings applied on aluminium alloy

The proposed work aims to develop and study sol–gel derived anticorrosion films for aluminium. To further improve performance of these films, organic corrosion inhibitors were incorporated into the films. The organic–inorganic hybrid films with and without corrosion inhibitors were deposited on an aluminium substrate by dip coating. The films were characterized by electrochemical impedance spectroscopy (EIS), DC polarisation techniques, and neutral salt spray test to evaluate their anticorrosion properties. This study shows that very low and very high MBT concentrations deteriorate the corrosion performance of coatings, and consequently, there is an optimum concentration of MBT. EIS results revealed a higher corrosion inhibitive activity of 2-mercaptobenzothiazole (MBT) compared to that of 2-amino-5-methylthiazole and 1,2,3 benzotriazole.     

Effects of serum proteins on corrosion behavior of ISO 5832–9 alloy modified by titania coatings

Stainless steel ISO 5832–9 type is often used to perform implants which operate in protein-containing physiological environments. The interaction between proteins and surface of the implant may affect its corrosive properties. The aim of this work was to study the effect of selected serum proteins (albumin and γ-globulins) on the corrosion of ISO 5832–9 alloy (trade name M30NW) which surface was modified by titania coatings. These coatings were obtained by sol–gel method and heated at temperatures of 400 and 800 °C. To evaluate the effect of the proteins, the corrosion tests were performed with and without the addition of proteins with concentration of 1 g L^?1 to the physiological saline solution (0.9 % NaCl, pH 7.4) at 37 °C. The tests were carried out within 7 days. The following electrochemical methods were used: open circuit potential, linear polarization resistance, and electrochemical impedance spectroscopy. In addition, surface analysis by optical microscopy and X-ray photoelectron spectroscopy (XPS) method was done at the end of weekly corrosion tests. The results of corrosion tests showed that M30NW alloy both uncoated and modified with titania coatings exhibits a very good corrosion resistance during weekly exposition to corrosion medium. The best corrosion resistance in 0.9 % NaCl solution is shown by alloy samples modified by titania coating annealed at 400 °C. The serum proteins have no significant effect onto corrosion of investigated biomedical steel. The XPS results confirmed the presence of proteins on the alloy surface after 7 days of immersion in protein-containing solutions.     

Corrosion protection of AA6061-T4 alloy by sol–gel derived micro and nano-scale hydroxyapatite (HA) coating

Micron and nano-scale hydroxyapatite (HA) were coated successfully on AA6061-T4 substrates by sol–gel method. Besides, the effects of coating thickness on adhesion strength and corrosion behaviour of the coatings were studied. Corrosion resistance was measured by potentiodynamic polarization test using a potentiostat under in vitro conditions. The coatings before and after corrosion tests were characterized by adhesion tests, a scanning electron microscopy attached with EDS and X-ray diffraction analysis. The results revealed that all the coatings exhibit a passive behaviour in Ringer’s solution. Specimens coated with nano-scale HA had the higher corrosion resistance than micro-scale coatings. The highest corrosion resistance appeared to be for the ~30 μm nano-scale HA coated substrates. However, for micro-scale HA coatings, the highest adhesion resistance was obtained at ~30 μm film thickness.     

Effect of the synthesis conditions on the formation of MgSrP2O7 and its characterisation for pigmentary application

In present research, we examined MgSrP₂O₇ as a new pigment with focus on its application as a corrosion inhibitor. The influence of the synthesis’ conditions on the product properties was examined. Samples were obtained by solid-state reaction and various homogenisation methods of initial components were employed (hand-milling, wet (ethanol/acetone) ball-milling and coprecipitation). Thermal behaviour of the reaction mixtures or dried coprecipitate was investigated using differential thermal and thermo-gravimetric analyses. Obtained samples were characterised with X-ray diffraction analysis, scanning electron microscopy and IR spectroscopy. Focusing on pigmentary application, specific properties of the samples were evaluated, such as thermal stability, mean particle size values and colour parameters, and also preliminary anticorrosion tests have been performed. Based on obtained results, MgSrP₂O₇ could be considered as a perspective corrosion inhibitor and homogenisation via coprecipitation can be rated as the best method of preparation of this composition, which provides the best thermal stability, the lowest particle size, the best homogeneity and the most promising corrosion inhibition characteristics (pH and ρ of the pigment aqua suspension) for the final product.     

TiO_2/316L不锈钢薄膜电极在NaCl溶液中的耐腐蚀性能

应用sol gel法和提拉技术于 316L不锈钢表面构筑纳米TiO2薄膜,再经水热后处理以消除膜中的细小龟裂.SEM和XRD技术表征膜的形貌和厚度,线性极化法分别考察膜厚度、pH、和Cl浓度对纳米膜电极耐腐蚀性能影响.电化学交流阻抗检测纳米TiO2膜在 0. 5mol/LNaCl溶液中的阻抗随浸泡时间的变化,光电子能谱技术测定了经浸泡 1008h后的纳米膜中各元素相对百分含量和价态.结果表明:在中性或碱性条件下,厚度为 375~464nm的纳米膜其耐腐蚀性随浸泡时间的延长呈现初期增加而后稳定,浸泡 48h后腐蚀电流较之浸泡初期降低 2个数量级,耐腐蚀电阻增加 2个数量级,在浸泡 1 008h内没有发现腐蚀的产物,Fe是以原子态扩散到膜中.     

Protective Properties of a Sol-Gel Coating on Zinc Coated Steel

Galvanised and galvannealed steels are widely used due to their good corrosion resistance in aqueous solutions. However, when additional protection is required, organic coatings, corrosion inhibitors or conversion coatings are used to improve their corrosion protection. In this work, sol-gel coating was used to improve the corrosion behaviour of these two materials. This paper analyses the final protective properties of a sol-gel coating prepared by basic catalysis and its dependence on the sintering temperature and time of treatment. The influence of the sintering conditions on the galvanised and galvannealed substrates is a decisive factor for the coating quality and for the barrier affect against the aggressive media. While heat treatment time is the controlling factor for the galvannealed steels, the temperature is determining in the case of the galvanised. Corrosion mechanisms for sol-gel galvanised steels did not changed with respect to the uncoated steel. However for galvannealed steel, after coating the mechanism is not purely cathodic.     

The influence of surface modification of lithium zinc phosphate pigment on corrosion inhibition of mild steel and adhesion strength of epoxy coating

In this paper, the influence of sol–gel surface modification of lithium zinc phosphate (LZP) pigment by methacryloxy propyl trimethoxy silane on corrosion inhibition, dispersion stability and adhesion strength was studied. IR spectroscopy and thermogravimetric analysis confirmed that organic functional group was successfully grafted onto the LZP surface. EIS and polarization measurements of mild steel showed an improvement in corrosion resistance for the extract of surface modified pigment in 3.5 % NaCl solution which was connected to better solubility proved by ICP-OES. The dispersion stability of the pigment in epoxy resin was found to be improved after surface modification. In addition, the adhesion strength of the epoxy coating containing surface modified pigment to mild steel after exposure to salt spray (5 % NaCl solution) was enhanced. The sol–gel surface modification had led to increase in hydrophobicity of the pigment particle surface, but simultaneously increased solubility of the pigment in water possibly due to the lower degree of agglomerates or aggregates of the pigment particles.     

Behaviour of surface-treated mica and other pigments with lamellar particles in anticorrosive coatings

The paper deals with using lamellar pigments for anticorrosive barrier coatings. By depositing a ferric oxide layer on a muscovite particle a pigment is obtained, which being applied to coatings improves the mechanical properties thereof, resistance to UV radiation and acts as an anticorrosion barrier. The optimum concentration of lamellar surface-treated muscovite in the coatings amounts to 20 vol. %.     

Features of formation of magnetite coatings on low-carbon steel in hot nitrate solutions

The process of anticorrosion magnetite coating (MC) formation on low-carbon steel is studied in alkali-free nitrate converting media at the temperatures of 70–98°C reduced as compared to those used (130–145°C) in standard technologies of steel bluing: formation of such coatings in alkaline nitrate solutions. Alongside with the conventional corrosion-electrochemical methods of analysis of the formed MCs, the regularities of the MC surface reliefs were studied using the method of atomic force microscopy combined with the technique of flicker-noise spectroscopy (FNS) for processing digitized images and obtaining the parameters of the MC surface structure in different nanometer ranges. It was shown that it is necessary to introduce additives of metal nitrates with a low cation radius into the ammonium nitrate converting solution to obtain MCs with a high corrosion stability at the first stage of MC formation and the final stage must consist in the further “passivation” of MCs: MC treatment by aqueous solutions based on nontoxic carboxylates. According to the FNS analysis of the surface structure of the formed MCs, a significant decrease of the FNS “point” factor, an indicator of MC corrosion instability, occurred during the final treatment. On this basis, one could characterize quantitatively the results of accelerated corrosion tests: no steel corrosion occurred on the thus formed coatings for 42 days under standard severe conditions: 100% relative humidity and daily “showering”. The performed study reveals fundamental possibilities for solving the problems of standardization of the anticorrosion coating surface based on the analysis of their surface profile in the nanometer range.     

Characterization and anticorrosive properties of poly(2,3‐dimethylaniline)/nano‐Al2O3 composite synthesized by emulsion polymerization

Poly(2,3‐dimethylaniline)/nano‐Al₂O₃ composite (PAC) was synthesized by emulsion polymerization using dodecyl benzene sulfonic acid as emulsifier and dopant. The structure of PAC was characterized by Fourier fransformation infrared spectroscopy, UV–visible adsorption spectroscopy, and field emission scanning electron microscopy. The thermal stability was studied by thermogravimetric analysis, and the electrochemical performances were studied by cyclic voltammetry measurements. Epoxy coatings containing PAC and poly(2,3‐dimethylaniline) (P(2,3‐DMA)), respectively, were painted on steel, and accelerated immersion tests were performed to evaluate the anticorrosion property of the coatings in 3.5% NaCl solution. The results showed that the addition of PAC and P(2,3‐DMA) could improve the anticorrosion performance of epoxy coating significantly and the PAC coating had higher corrosion resistance than that of P(2,3‐DMA). Copyright © 2013 John Wiley & Sons, Ltd.     

Mechanical and corrosion behavior of amorphous and crystalline electroless Ni–W–P coatings

Two types of electroless Ni–W–P coatings: nanocrystalline with low P and amorphous with higher P content are investigated. Scanning probe microscopy is applied to study their morphology. Textured nanocrystalline coatings consist of coarse pyramids built of nanometer thick lamellas. The surface morphology of amorphous coatings is much finer and uniform. Nanohardness of all coatings depends on W content. Microhardness is increasing during the heat treatment up to 350 °C due to nickel phosphide precipitation affected by tungsten also. The wear resistance of nanocrystalline Ni–W–P coatings is much higher than that of amorphous in spite of the similar tungsten content in both. Lower corrosion resistance of amorphous Ni–W–P coatings is found by weight loss method during long-term immersion in 5 % NaCl. Electrochemical tests by potentiodynamic polarization curves in two model corrosion media—solutions of 0.5 M H₂SO₄ and 5 % NaCl—are performed. The corrosion of bi-layered Ni–W–P/Ni–P and Ni–W–P/Ni–Cu–P deposits on mild steel is also investigated. The results prove that an electroless Ni–W–P coating on mild steel extremely improves its mechanical and corrosion behavior. It is demonstrated that in addition to deposit’s structure and composition, the distribution and chemical state of alloy ingredients are also responsible for its properties.     

Excellent protection of mild steel in sodium chloride solution for a substantial period of time using a hybrid nanocoating of poly vinyl alcohol and Titania

The production of eco-friendly hybrid sol–gel coatings for long term protection of metallic substrates from aggressive environments was one of the emerging areas, competing with conventional chromate and phosphate coatings. Herein, a nanocomposite has been synthesized from TiO₂ and PVA through a novel sol-gel route and the structure and morphology of the same was characterized using X-ray diffraction, FTIR, UV–Vis spectroscopy, FESEM with EDAX, and AFM studies. The flower-like structured composite offers excellent corrosion protection properties in NaCl solution of sea water salinity. Impedance and polarization studies were carried out to monitor the anticorrosion performance of the materials coating. This coating on mild steel offers 98% inhibition efficiency in NaCl. The influence of loading PVA on TiO₂ and its effect on corrosion efficiency have also been investigated. It is found that an optimum weight of 20 wt% PVA is required in the composite for beneficial corrosion resistance. 92% inhibition efficiency is registered by the coated MS in NaCl solution after 40 days of exposure and is quite encouraging compared to many of the recent reports. The Ti–O–Ti, and Fe-Ti-O linkage along with compactness and adherence of the material together contribute to better blocking of steel corrosion.     

Special anticorrosion coatings (sealing pastes) for high-strength steel resistance spot welding

The results of application of new anticorrosion coatings (sealing pastes) during resistance spot welding, which provide for protection of weld joints from corrosive action, are given. The studied anticorrosion coatings (sealing pastes) are proved to allow for flawless weld joints of 30KhGSN2A and Kh15N5D2T steel without degrading their mechanical properties.     

Corrosion protection of carbon steel using a combination of Zr conversion coating and subsequent zinc-rich silicate coating with a flake ZnAl alloy

To improve the corrosion protection properties of zinc-rich silicate coatings on steel, zirconium pretreatment loaded with (3-aminopropyl)triethoxysilane (APTES) 0.025 % (v/v) and the partial replacement of spherical zinc by flake ZnAl alloy were investigated. DC polarization and electrochemical impedance spectroscopy (EIS) show that the zirconium pre-treated layer containing APTES improves the corrosion protection of the bare steel. Zinc-rich silicate coatings containing flake ZnAl with and without pretreatment were evaluated by EIS, salt spray test and pull-off test. Pretreatment with a zirconium conversion layer reduces corrosion products and adhesion loss (from 16.53% to 12.54%) while the performance of corrosion protection significantly increased from 2003 Ω.cm² to 2640 Ω.cm² in comparison with the non-pretreated samples. The results show that flake ZnAl pigment (5 wt%) significantly improves corrosion resistance and prolongs the duration of cathodic protection of zinc-rich silicate coatings.     

Electrochemical corrosion resistance performance of sustainable resource-based nanoconducting polymer composites in alkaline medium

The corrosion resistance performance of poly (otoluidine) (POT)-dispersed castor oil-polyurethane, (COPU) nanocomposite coatings, POT/COPU, with three different compositions (i.e. 0.25, 0.5 and 1.0 wt%) in alkaline medium is studied. The coatings are applied on mild steel specimens by brushing. Corrosion resistance behaviour of these coatings is investigated using potentiodynamic polarization measurements, electrochemical impedance spectroscopy (EIS) and by weight loss. The morphological behaviour of corroded and uncorroded coated specimens is investigated by scanning electron microscopy (SEM). It is interesting to report that the presence of conducting polymer nanoparticles in POT/COPU coatings suppresses the saponification of COPU in an alkaline environment. These investigations show that the dispersion of POT in COPU remarkably improves the corrosion resistance performance of COPU in alkaline media. POT/COPU (1.0 wt%) coatings have potential as anticorrosive-coating materials in alkaline media at higher pH. These coatings have a higher resistance to alkaline medium in comparison to other compositions.     

Study of the resistances of organic coatings to filiform corrosion

The filiform corrosion is a special-type atmospheric corrosion, which broadens below the organic coatings and is characterized by its manifestation in the form of fibres or filaments. An important factor for broadening the filiform corrosion involves also the barrier or chemical resistance of the organic coating. The paper deals with the modes of filiform-corrosion initiation and evaluation thereof under nonpigmented organic coatings based on various binder bases. Also the possibility of retardation of the filiform corrosion by means of zinc powder and the effects of lamellar pigment on the filament shapes are studied.     

Sol–Gel-Derived Corrosion-Protection Coatings

There is a current need for alternative coatings that can provide corrosion resistance to metals or alloy surfaces due to the environmental hazards posed by conventional coatings. Herein, we report on novel organically-modified sol–gel coatings for the protection of metal and alloy surfaces. The basic concept of chemical conversion of metal surfaces is based on deposition of a hydrophobic, nonporous sol–gel barrier layer for surface protection and corrosion prevention. The properties of these organosilica coatings can be tuned by varying the composition of precursors. The evaluation of hydrophobicity, adhesive strength, and anticorrosion properties of organically-modified sol–gel derived coatings suggests their potential utility as technologically-compatible alternatives to conventional coatings.