Galvanic function of zinc-rich coatings facilitated by percolating structure of the carbon nanotubes. Part II: Protection properties and mechanism of the hybrid coatings

Innovative zinc-rich hybrid paint coatings were developed using nano-size particles composed of alumina hydrate modified with polystyrene-sulfonate (PSS) doped polypyrrole (PPy) and either purified or functionalised multi-walled carbon nanotubes (MWCNTs). General properties of the particles and their dispersions were characterised in 1st part of the work. Corrosion protection characteristics of the hybrids were examined on low-carbon steel panels by immersion and salt-spray chamber tests. Immersion tests were monitored by electrochemical impedance spectroscopy (EIS). Primers were analysed by glow-discharge optical emission spectroscopy (GD OES) and surface of the steel substrates was investigated by X-ray photoelectron (XPS) and FT-Raman spectroscopy. Improved barrier and galvanic function of the hybrids over traditional zinc-rich paints (ZRPs) were evidenced by performance metrics. Optimal protection characteristics were found when content of the particles was close to the statistical and kinetic percolation thresholds. Advanced protection mechanism of the hybrids is discussed on function of the nano-size filler benefiting the utilisation of sacrificial current output of the anodic zinc along with taking into account aspects of the multiple percolation theory. The interpretation given in this work is intended to facilitate design of next generation of corrosion protecting metal-rich coatings.     

The improvement of anticorrosion properties of zinc-rich organic coating by incorporating surface-modified zinc particle

The corrosion behaviors of zinc-rich coating with various zinc contents, ranging from 0 to 60 volume percent, in thin organic coatings (below 5 μm) were characterized by electrochemical impedance spectroscopy (EIS), free corrosion potential (E_corr) measurement and cycle corrosion test (CCT). It was verified that both coatings with 60 volume percent of zinc powder and without zinc powder showed good corrosion resistance mainly due to the cathodic protection and barrier effect, respectively. On the other hand, coatings with an intermediate concentration (10–40 vol.%) of zinc powder was not successful in protecting a steel substrate efficiently. To improve anticorrosion property of zinc-rich coating, the surface modification of zinc particle was carried out with derivatives of phosphoric and phosphonic acid in the aqueous solution. The effects of the surface modification of zinc particle on corrosion resistance of the coating were investigated with scanning vibrating electrode technique (SVET) and X-ray photoelectron spectroscopy (XPS). The best anti-corrosion performance was achieved when the incorporated zinc particle was treated with phosphoric acid 2-ethylhexyl ester and calcium ion simultaneously, which induced the formation of alkyl-phosphate-calcium complex layer of 190 nm in thickness on zinc particles. Corrosion resistance was improved by the decreased zinc activity and the increased compatibility between the formed complex layer on zinc surface and polymer binder matrix.     

Anticorrosive polyurethane paints with nano- and microsized phosphates

Two types of phosphate fillers (nanosized aluminum phosphate and microsized aluminum–zinc phosphate) were tested as anticorrosive fillers in 2 K solvent-borne polyurethane paints based on commercial acrylic resin with OH groups and an isophorone diisocyanate-type hardener. Three coating compositions containing commercial fillers (mica/quartz, TiO₂, wollastonite, talc) and also mentioned nanosized aluminum phosphate or microsized aluminum–zinc phosphate were prepared using a pearl-mill as well as a laboratory dissolver, applied onto a steel substrate and cured at room temperature for 14 days. An influence of the type and content of a phosphate filler on properties of polyurethane paints and coatings has been investigated. Incorporation of nanosized aluminum phosphate into coating compositions increases their viscosity while cured paints exhibit reduced adhesion to steel substrates. The results of corrosion tests in a salts spray chamber as well as immersion in an aqueous NaCl solution indicated that the paint system with 9.8 wt.% of applied nanofiller had similar protective properties to a polyurethane coat containing a higher dose (i.e. 15.6 wt.%) of commercial microsized aluminum–zinc phosphate.     

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.     

Anticorrosive properties of polypyrrole films modified with zinc onto SAE 4140 steel

Polypyrrole (PPy) films modified with zinc were electrosynthesized onto SAE 4140 steel in presence of bis(2-ethylhexyl) sulfosuccinate (AOT). The Zn and PPy electrodeposition was realized by using cyclic voltammetry at different temperatures. The corrosion protection properties of the films were examined in chloride solution by open circuit measurements, linear polarization and electrochemical impedance spectroscopy (EIS). The obtained results indicate that the presence of Zn in the polymer matrix improves the anticorrosive performance of PPy films. The best anticorrosion efficiency was obtained for the coatings modified at 20 °C which provided anodic protection to the steel substrate for a long period of immersion in chloride solution. Cathodic protection was observed when the electrodeposition temperature was increased. Adherence and anticorrosive properties declined sharply for the coatings electrosynthesized at 5 °C.     

Evaluation of an environmentally friendly anticorrosive pigment for alkyd primer

An alkyd formulation containing zinc phosphate (10 wt.%) was prepared and subsequently modified replacing the latter anticorrosive additive by a very low concentration of conducting polymer. Specifically, three modified paints, which contain polyaniline emeraldine base (undoped form), polyaniline emeraldine salt (doped form) and an eco-friendly polythiophene derivative (partially oxidized), were formulated. The properties and corrosion resistance of the four alkyd coatings have been characterized. Among the three modified paints, the one containing polythiophene shows the best adherence and the highest corrosion resistance. This has been attributed to the fact that the miscibility of the polythiophene derivative with the alkyd formulation is better than that of polyaniline. Furthermore, accelerated corrosion assays and electrochemical impedance spectroscopy measurements revealed that the corrosion resistance of the paint with polythiophene is several orders of magnitude higher than that with zinc phosphate. The polythiophene derivative has been found to induce the formation of a passivating and well-adhered layer between the coating and the surface, preventing the access of chloride anions and oxygen to the substrate.     

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.     

Zinc-rich powder coatings corrosion in sea water: influence of conductive pigments

The effect of addition of conductive pigments like carbon blacks on the corrosion behavior of zinc-rich powder paints coated steel in artificial sea water was investigated. Open circuit potential measurements were used to characterize the cathodic protection ability and duration. Micro-Raman spectroscopy analysis was performed in order to identify the corrosion products and to follow the penetration of the solution inside the coatings.

Two different effects were pointed out: an increase of the porosity induced by carbon addition and a galvanic action between zinc and carbon pigments. The performance of the powder coatings, strongly improved if the carbon amount is sufficient, was compared to the one reported for solvent-based zinc-rich paints.     

Application of silica-containing nano-composite emulsion to wall paint: A new environmentally safe paint of high performance

A new emulsion-type paint was prepared by utilizing a nano-composite emulsion (NCE), which contained nano-size particles (ca. 60 nm in diameter) consisting of silica (inorganic core, ca. 30 nm in diameter) and polyacrylate (organic shell), and evaluated as wall paint. By applying NCE for the wall paint, about 35 wt.% of the organic content in the paint could be reduced in comparison with the commodity emulsion-type paint, which is highly effective to save the petroleum resources. The basic properties of the white NCE paint film on gloss, surface hardness, adhesion, and solvent resistance were evaluated and compared with those of acrylic emulsion-type paints as well as those of silica-containing paints which were prepared simply by blending the acrylic emulsion with silica sol. The NCE paint was especially excellent in solvent resistance. Then the practical tests were performed to evaluate its appropriateness as wall paint, which clarified the excellent antipollution property and the high flame resistance of the NCE paint.     

Electrochemical and anticorrosion performances of zinc-rich and polyaniline powder coatings

In this work, hydrochloride polyaniline (PANI-Cl) powder was incorporated as a conductive pigment into powder zinc-rich primer (ZRP) formulations in order to enhance the electronic conduction paths between zinc particles inside the coating and the steel substrate (i.e. percolation). Coatings were applied onto steel substrates and immersed in a 3% NaCl solution at ambient temperature.The protective properties and electrochemical behaviour of coatings were investigated by monitoring the free corrosion potential versus time and by using EIS. It was found that corrosion potential remains cathodic and constant for a long time up to 100 days of immersion. From EIS results, it was shown that the coatings exhibit larger impedance values than those observed with liquid or other zinc-rich powder formulations containing carbon black. From Raman spectroscopy results, it may be proposed that zinc particles in contact with PANI-Cl pigments were passivated. Other zinc particles remain still active which ensures the cathodic protection of the substrate. Moreover, coatings exhibit good barrier properties.     

Galvanic function of zinc-rich coatings facilitated by percolating structure of the carbon nanotubes. Part I: Characterization of the nano-size particles

The newly developed zinc-rich hybrid paints are composed of polypyrrole (PPy) and polystyrene-sulfonate (PSS) modified alumina hydrate and either purified or functionalized multi-walled carbon nanotubes (MWCNTs). Preparation of the nano-size particles, i.e., in situ polymerization and deposition of PPy-PSS complexes on the mixture of alumina hydrate and MWCNTs is presented. Characterization of the particles by cyclic voltammetry (CV), Fourier-transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM) as well as their dispersions by rheology investigation is detailed in this part of the work. High electrochemical reversibility, increasing electrical conductivity and Coulombic efficiency of the particles with greater relative amount of the MWCNTs were evinced. Thin layer polymer deposition was found continuous on alumina and the MWCNTs and varied compactness of the PPy films and charge-delocalization over their network were witnessed depending on the proportion of incorporated PSS. Different micron-scale dispersity of the particles, compactness and ramification of particle clusters as well as their aggregation at nano-scale and flocculation at micron-scale were disclosed resulting in either kinetically three-dimensional (3D) interacting or non-percolating distribution. Corrosion protection performance of the hybrid coatings was examined whereas characteristics of the protection mechanism is substantially analysed from many perspectives, which all detailed in 2nd part of this study.     

Application of EIS and salt spray tests for investigation of the anticorrosion properties of polyurethane-based nanocomposites containing Cr2O3 nanoparticles modified with 3-amino propyl trimethoxy silane

The Cr₂O₃ nanoparticles were modified with 3-amino propyl trimethoxy silane in order to obtain proper dispersion and increment compatibility with the polyurethane coating matrix. The nanocomposites prepared were applied on the St-37 steel substrates. The existence of 3-amino propyl trimethoxy silane on the surface of the nanoparticles was investigated by Fourier transform infrared (FTIR) spectroscopy and thermal gravimetric analysis (TGA). Dispersion of the surface modified particles in the polyurethane coating matrix was studied by a field emission-scanning electron microscope (FE-SEM). The electrochemical impedance spectroscopy (EIS) and salt spray tests were employed in order to evaluate the corrosion resistance of the polyurethane coatings. Polarization test was done in order to investigate the corrosion inhibition properties of the Cr₂O₃ nanoparticle on the steel surface in 3.5 wt.% NaCl solution. The adhesion strengths of the coatings were evaluated by pull-off adhesion tester before and after 120 days immersion in 3.5 wt.% NaCl solution. FT-IR and TGA analyses revealed that surface modification of the nanoparticles with 0.43 silane/5 g pigment resulted in the greatest amount of silane grafting on the surface of particles. Results obtained from FE-SEM analysis showed that the surface modified nanoparticles dispersed in the coating matrix properly. Results obtained from EIS and salt spray analyses revealed that the surface modified particles enhanced the corrosion protection performance of the polyurethane coating considerably. The improvement was more pronounced for the coating reinforced with 0.43 g silane/5 g pigment. Moreover, the adhesion loss decreased in the presence of surface modified nanoparticles with 0.43 silane/5 g pigment.     

Study of epoxy and alkyd coatings modified with emeraldine base form of polyaniline

In this work we examine the ability of the emeraldine base form of polyaniline to impart protection against corrosion when it is used as additive of commercial paints. For this purpose, three paints, which are used as primers in marine environments, were checked: two epoxy coatings that differ in the presence or absence of inorganic anticorrosive pigment (zinc) and one alkyd coating. In a first stage, the rheological, structural, thermal and mechanical properties of the three coatings were characterized using viscosity measurements, infrared spectroscopy, thermogravimetric analyses and stress–strain assays, respectively. Furthermore, we observed that the resulting properties were not altered by the addition of a low concentration of polyaniline (0.3%, w/w). Accelerated corrosion tests were performed to compare the degree of protection of both the modified and unmodified paints. The polyaniline did not affect to the protective properties of the epoxy without inorganic anticorrosive pigment nor the alkyd formulations. In opposition, the polyaniline added to the epoxy paint with inorganic anticorrosive pigment induced the formation of a zinc oxide layer, which promoted the corrosion attack.     

Comparison of the efficiency of inorganic nonmetal pigments with zinc powder in anticorrosion paints

This paper deals with the study of properties of anticorrosion pigments of varying chemical composition in epoxyester paints. Two type lines of paints were prepared. The first line comprised an anticorrosion pigment with a PVC concentration of 10% while the other line comprised an anticorrosion pigment with a PVC concentration = CPVC. The following nontoxic anticorrosion pigments were observed: zinc phosphate, zinc phosphomolybdate, calcium hydrogen phosphate, zinc phosphate modified with an organic corrosion inhibitor, strontium–aluminum polyphosphosilicate, zinc–aluminum polyphosphate, calcium metaborate, calcium ferrite, calcium borosolicate, and strontium chromate. The epoxyester primers were observed for the effect of the type of pigment on the anticorrosion properties. Anticorrosion efficiency was derived from tests in a condenser chamber and in a salt spray cabinet as well as from a test of chemical resistance of pigmented coatings. The evaluation of anticorrosion efficiency of inorganic nonmetal pigments was carried out by means of comparison with anticorrosion efficiency of metal dust.     

Glossy topcoat exterior paint formulations using water-based polyurethane/acrylic hybrid binders

The development of glossy topcoat one-pot exterior paint formulations using water-based polyurethane/acrylates hybrid binders as well as the assessment of its properties through different conventional tests is discussed in this work. Polyurethane (PU) anionomer having 2-ethoxymethacrylate terminal groups was prepared following a prepolymer mixing process. This prepolymer was chain extended in aqueous solution and after addition of acrylic monomers radical polymerized. Paints were prepared using titanium dioxide as unique pigment. Panels coated with air-dried paints with three pigment to volume concentration (PVC) values were subjected to standardized tests including adhesion, flexibility, gloss and color determination. Accelerated weathering tests were carried out to evaluate changes in properties, especially gloss and color, of painted panels. Solvent-based acrylic and polyurethane paints were included as high gloss quality reference coatings. It was found that air-dried formulations based on hybrid polyurethane/acrylic with up to 50 wt.% of acrylic component, show a gloss as high as 70 and the relative gloss change after accelerated weathering test is lower than the pure solvent-based acrylic and polyurethane paints.     

Electrodeposited Ni-B alloy coatings: Structure, corrosion resistance and mechanical properties

Ni-B alloy coatings with different boron content ranging from 4 to approximately 28 at.% were prepared by electrodeposition in a nickel-plating bath containing sodium decahydroclovodecaborate as a boron source. The influence of the boron concentration in the coatings on their structure, morphology, electrochemical and corrosion behavior, physico-mechanical and electrical properties was investigated using X-ray diffractometry (XRD), scanning electron microscopy (SEM), potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and other methods. It was found that the electrodeposited Ni-B coatings with relatively low boron content (≤8 at.%) are nanocrystalline and comprise a solid solution of boron in f.c.c. Ni lattice having a mixed substituted-interstitial type. Further increase in the boron content (up to 10-15 at.%) leads to the appearance of heterogeneous amorphous-nanocrystalline structure, and the coatings with a high boron content (20 at.% and above) are X-ray amorphous. Polarization measurements in neutral NaCl solutions showed that the Ni-B coatings with relatively low boron content demonstrate a potential region of low anodic currents associated with the passive film formation at the alloy surface. The anodic current in this potential region increases significantly with increasing the boron content above 10 at.%, suggesting the non-protective nature of the anodic film formed on the amorphous Ni-B alloys. Immersion tests monitored by EIS measurements revealed a significantly better corrosion performance of the Ni-B coatings with low boron content (4 at.%) in comparison with that of the amorphous coatings. The microhardness and wear resistance of the Ni-B coatings essentially increases with increasing the boron content. Maximum microhardness and wear resistance were found for the coatings containing 8 at.% B.     

Study of the anticorrosive behaviour of epoxy binders containing non-toxic inorganic corrosion inhibitor pigments

The anticorrosive performance of epoxy coatings pigmented with non-toxic corrosion inhibitors pigments was investigated in this work. The coatings used contained the following pigments: zinc phosphate (ZP), zinc phosphomolybdate (ZPM) and zinc calcium phosphomolybdate (ZCPM). For comparative studies epoxy coatings with the following compositions were made up: one only with filler (CRG); one without pigments, varnish (VR) and other with zinc chromate (ZC) pigment. The corrosion inhibitor performance of the coatings was evaluated by immersion tests in 0.01 mol L⁻¹ NaCl aqueous solutions and accelerated tests in a salt spray chamber. The corrosion inhibitor performance of the samples was monitored using open-circuit potential (E_oc) measurements and electrochemical impedance spectroscopy (EIS) technique. Complementary tests were carried out using water vapour permeability of free-standing films and thermogravimetric (TG) analysis. The permeability test showed that the addition of the studied pigments did not modify the barrier properties of the free-films in comparison that pigmented with chromate. Thermal analysis indicated that the addition of the pigments improved the thermal stability of the coatings and it suggested a resin/pigment interaction. The total immersion tests and salt spray tests demonstrated that the barrier properties of the coatings pigmented with the inhibitors were not degrading as much as that pigmented with ZC. Therefore, all the three pigments could replace ZC as an anticorrosive pigment in similar conditions to those described here. The best corrosion inhibitor performance in the total immersion test was presented by the ZPM and ZCPM coatings while in the salt spray test the corrosion inhibitor performance of all the three pigmented coatings was similar, suggesting that only in the less aggressive test is possible to detect any difference between the coatings with the non-toxic pigments.     

Electrochemical synthesis of polypyrrole (PPy) and PPyǀmetal composites on copper electrode and investigation of their anticorrosive properties

This study reports corrosion protection behaviour of various metal cations electrodeposited onto polypyrrole (PPy) coated copper (Cu) electrode. Before electropolymerization of pyrrole, the Cu electrode was passivated in 0.1 M oxalic acid via cyclic voltammetry method. After the coating process, metal cation electrodeposition onto PPy coating was carried out in 10⁻² M CuCl₂, ZnCl₂, FeCl₂ and NiCl₂ solutions. Corrosion behaviour of uncoated, PPy and PPy|metal coated Cu electrodes was studied in 0.1 M H₂SO₄ solution by using potentiodynamic polarization, chronoamperometric and impedance spectroscopic measurements. Surface morphologies were examined by scanning electron microscope (SEM). All the electrochemical measurements were in good agreement showing that metal electrodeposited PPy coated Cu electrodes have a higher corrosion resistance. Furthermore, SEM results show that while all the samples have a homogeneous distribution of metal cations, zinc and nickel have a much better homogeneous distribution compared to copper and iron. It was found that the best corrosion protection is provided by PPy|Zn and PPy|Ni coatings and there is a significant increase in their polarization resistance with increasing amounts of electrodeposited cations.     

Kinetic and mechanistic study of CO2 corrosion inhibition by cetyl trimethyl ammonium bromide

The kinetics of the inhibition of carbon dioxide (CO₂) corrosion on high purity iron (Fe) electrodes by cetyl trimethyl ammonium bromide (CTAB) were investigated in order to elucidate the mechanism of inhibition. The test condition was: 25 °C, 3 wt.% NaCl brine, pH 4, 1 bar CO₂ partial pressure. The inhibition process was studied by electrochemical methods and by X-ray photoelectron spectroscopy (XPS). The inhibition was found to be a combination of two processes: first a rapid process (order of minutes) connected to diffusion limited adsorption of the inhibitor, leading to the inhibition of the anodic part reaction, and a second slower process (order of hours) leading to a reduction in the corrosion rate through the inhibition of the cathodic part reaction(s).     

高锌粉含量的单组分环氧富锌底漆的研制

以自制的改性环氧树脂为基料,锌粉为防锈颜料,制备出干膜中锌粉含量达96%以上的单组分环氧富锌底漆。同时考察了影响漆膜防腐蚀性能和涂料贮存稳定性的因素。实验表明:锌粉的含量在95%～97%时,漆膜的防腐蚀效果最好,经过1 000 h的耐盐雾试验后,漆膜保持完好;采用0.2%有机膨润土和1%聚酰胺蜡搭配使用,有效地解决了单组分环氧富锌底漆中锌粉沉降结块的问题,根据实验结果得到最佳单组分环氧富锌底漆配方,同国外同类型的产品相比具有更好的性价比。漆膜性能优异,VOC含量较低,环保性能好。