Methodology for zinc phosphate pigment incorporation into polypyrrole matrix

In this work, the incorporation of a commercial zinc phosphate pigment into polypyrrole (PPy) matrix during its electrochemical synthesis on mild steel was studied in order to produce PPy/zinc phosphate composite films as a protective layer against corrosion. Potassium nitrate, oxalic acid, tosylic acid and sodium salicylate solutions were used as electrolytes in cyclic voltammetry and galvanostatic polarisation studies. The influence of synthesis parameters such as nature, concentration, pH and stirring of the electrolyte on the degree of incorporation of the pigment was investigated, as well as time and current densities of the electropolymerisation process. Their influence on current efficiency was also evaluated. Sodium salicylate was the only electrolyte to show a high current efficiency in the polymerisation reaction and to yield a composite film with a reasonable amount of zinc phosphate. In this electrolyte medium, X-ray photoelectron spectroscopy (XPS) analysis showed that zinc phosphate may be found in the polymeric matrix: (i) as a conductive ionic minority form and (ii) as a non-conductive non-ionic majority one for higher incorporation levels. Scanning electron microscopy (SEM) showed that zinc phosphate is heterogeneously distributed on the surface of the polymer.     

Effect of surface treatment of pigment particles with polypyrrole and polyaniline phosphate on their corrosion inhibiting properties in organic coatings

The effect of pigment particle surface treatment with conductive polymers on the corrosion inhibiting properties of organic paints was investigated. Mixed oxides possessing the spinel and perovskite structures were synthesised for the study. Natural graphite and pigments based on ferric oxide and silicate were studied. Coating materials based on a water-based epoxy resin were prepared for the investigation of the corrosion protection properties of the pigments, the surfaces of which had been provided with a conductive polymer layer. Laboratory corrosion tests were applied to the paint films. A commercial corrosion protection pigment, based on modified zinc phosphate, served as the corrosion protection efficiency standard. Polyaniline phosphate was found preferable to polypyrrole as the modifying agent of the pigment surface regarding the pigment's corrosion inhibiting efficiency. Surface treatment with the conductive polymers is also beneficial to the mechanical properties of the paint.     

Performance of zinc phosphate coatings obtained by cathodic electrochemical treatment in accelerated corrosion tests

The formation of zinc phosphate coating by cathodic electrochemical treatment and evaluation of its corrosion resistance is addressed. The corrosion behaviour of cathodically phosphated mild steel substrate in 3.5% sodium chloride solution exhibits the stability of these coatings, which lasts for a week's time with no red rust formation. Salt spray test convincingly proves the white rust formation in the scribed region on the painted substrates and in most part of the surface on unpainted surface. The protective ability of the zinc corrosion product formed on the surface of the coated steel is evidenced by the decrease in the loss in weight due to corrosion of the uncoated mild steel, when it is galvanically coupled with cathodically phosphated mild steel. Potentiodynamic polarization curves reveal that E_corr shifts towards higher cathodic values (in the range of −1000 to −1100 mV versus SCE) compared to that of uncoated mild steel and conventionally phosphated mild steel substrates. The i_corr value is also very high for these coatings. EIS studies reveal that zinc dissolution is the predominant reaction during the initial stages of immersion. Subsequently, the non-metallic nature of the coating is progressively increased due to the formation of zinc corrosion products, which in turn enables an increase in corrosion resistance with increase in immersion time. The zinc corrosion products formed may consist of zinc oxide and zinc hydroxychloride.     

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.     

Cathodic disbondment of epoxy coating with zinc aluminum polyphosphate as a modified zinc phosphate anticorrosion pigment

As an approach to improve the resistance of protective coatings to the disbondment, modification of the formulation through incorporation of zinc aluminum polyphosphate anticorrosion pigment representing third generation phosphates was examined in this paper. The data obtained from cathodic disbonding test, electrochemical impedance spectroscopy and pull-off indicated that introduction of zinc aluminum polyphosphate within epoxy coating could provide improved resistance to cathodic disbonding as well as superior adhesion strength. The superiority in the presence of the modified pigment was connected to deposition of a layer at the disbonding front and locally controlled pH as well. The precipitation restricting active zone available for electrochemical reaction was confirmed by SEM.     

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.     

Optimization of potassium zinc phosphate anticorrosion pigment by Taguchi experimental design

The synthesis condition of potassium zinc phosphate pigment was optimized with respect to corrosion inhibition in extract solution and dispersion stability in an epoxy resin by application of Taguchi experimental design. Processing parameters, including calcinations time, quiescent time, mixing rate and KOH/ZnCl₂ mole ratio are selected as the influential parameters. Corrosion inhibition of the pigments in the extract solutions and dispersion stability in the epoxy resin were evaluated by electrochemical impedance spectroscopy (EIS) and turbidity measurement, respectively. The pigment synthesized under optimal condition was characterized by XRD, which showed formation of KZnPO₄ and KZn₂PO₄(HPO₄). Corrosion protection of the epoxy coating containing synthesized pigment at optimal condition was evaluated by salt spray and compared to the unpigmented epoxy coating. Salt spray results showed higher corrosion protection of the epoxy coating in the presence of potassium zinc phosphate, which could be attributed to lower diffusivity of the pigmented coating to Cl⁻ or formation of phosphate layer confirmed by SEM–EDX.     

Improving the formation and protective properties of silane films by the combined use of electrodeposition and nanoparticles incorporation

The electrodeposition and nano-silica incorporation were used together to prepare the novel composite dodecyltrimethoxysilane/SiO₂ thin films from silane sol-gel system on aluminum substrate. The results showed that both the two techniques can improve the films formation and their protectiveness. The influences of the deposition potential and the silica content in silane solution were investigated. A “critical deposition potential” and a “critical silica content” were both observed, under which the obtained silane films had the highest protective properties. The enhancement in film thickness has been detected by these two techniques from the elemental depth profiles of silane films as measured by secondary-ion mass spectroscopy (SIMS). Current-time curves were on-line recorded on aluminum electrodes in silane solutions. As compared with that in blank solution, the current response was found to be larger in silica-contained precursor, probably suggesting that the silica particles participate in the film deposition.     

Corrosion electrochemical behavior of epoxy anticorrosive paints based on zinc molybdenum phosphate and zinc oxide

Electrochemical impedance spectroscopy (EIS) was applied as a principal tool to describe the efficiency of anticorrosive epoxy paints (primers) based on zinc molybdenum phosphate (ZMP) pigment. Steel-coated samples were exposed to a 0.5 M NaCl solution. During the study the corrosion potential (E_oc) and R_p values also were monitored every 24 h. It is discussed the incorporation of micronized ZnO (1 μm) pigment to the base mixture and its positive, reinforcement effect on the protective properties of ZMP primer. The explanation is related to the izoelectric point (IEP) of ZnO particles (pH < 9), which determines their positive surface charge and electrostatic attraction with the molybdate anion. In this case the charge of the formed double layer capacitor is very high. Moreover, the mentioned attraction inhibits and saves ZnO particles from their rapid dissolution to hydroxide.     

Corrosion protection properties of polypyrrole electropolymerized onto steel in the presence of salicylate

The corrosion performance of a polypyrrole coating constituted by hollow rectangular microtubes was monitored in chloride solutions using open circuit potential measurements, potentiostatic polarization and electrochemical impedance spectroscopy. The coating was electrosynthesized onto 316 L stainless steel from a salicylate solution and it provided a very good corrosion resistance to the substrate. It was found that polypyrrole films with granular morphology electrodeposited from a salicylate solution with lower concentration behave better in terms of protective behavior. In order to improve the corrosion protection imparted by the polypyrrole coating formed by the microtubes a system of two layers was electrodeposited, the first one consisted of polypyrrole with a granular morphology and the second one, on the top, was constituted by the microtubes. This bilayered system exhibited an excellent protective behavior during considerably long immersion time.     

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 mild steel by polypyrrole phosphate composite coating

Electrodeposition of polypyrrole phosphate (PPy–P) on mild steel (ST₁₂) was achieved in oxalic acid medium using cyclic voltammetry (CV) technique. Adherent and homogeneous PPy–P films were obtained. The corrosion behavior of mild steel with phosphate (PPy–P) coatings in 3.5% NaCl solutions was investigated through potentiodynamic polarization technique, open circuit potential–time curves, and electrochemical impedance spectroscopy (EIS). Based on a physical model for the corrosion of mild steel composite, the Zview (II) software was applied to the EIS to estimate the parameters of the proposed equivalent circuit. It was found that the PPy–P coatings could provide much better protection than PPy. The effect of phosphate on the morphology and structure of the passive film was investigated by scanning electron microscopy and electron dispersion X-ray analysis (EDX). The results reveal that the PPy–P coated electrode provided a noticeable enhancement of protection against corrosion process.     

Investigation on zinc phosphate effectiveness at different pigment volume concentrations via electrochemical impedance spectroscopy

This research is based on studying corrosion inhibitive effect of zinc phosphate at different pigment volume concentration (PVCs) in epoxy-polyamide system. EIS has been examined at open circuit potential (OCP) after 7 days of immersion in 3.5% NaCl solution to indicate electrochemical properties of epoxy coated mild steel at different levels of pigmentation. Coating capacitance, coating resistance, double layer capacitance and charge transfer resistance have been extracted from fitting of EIS results with an electrical circuit, while impedance magnitude at 100 mHz and phase angle (θ) at 10 kHz have been extracted directly from bode plots. Also OCP behavior was examined. Results showed best performance at PVC = 36.5%.     

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.     

Electrochemical properties of polypyrrole/sulfonted SEBS composite nanofibers prepared by electrospinning

The electrochemical behavior of electrospun polypyrrole (PPy)/sulfonated-poly(styrene-ethylene-butylenes-styrene) (S-SEBS) composite nanofibers was investigated, compared to PPy/poly(styrene-ethylene-butylenes-styrene) (SEBS) fibers prepared by a casting method. The electrospun PPy/S-SEBS (E-PSS) fibers were about 300 nm in average diameter, while PPy/SEBS composite (C-PS) prepared by a casting method showed the granular macroporous structure. The effect by both electrospinning and sulfonation results in higher electrochemical capacity due to the increase of doping level, high electrical conductivity, low interfacial resistance, and high reversibility by easy intercalation of Li ion. In addition, sulfonated SEBS induces higher elongation force to jet in the processing of electrospinning due to the role of dopant.     

The electrochemical synthesis of polypyrrole at a copper electrode: corrosion protection properties

Pyrrole was successfully electropolymerized at a copper electrode in a near neutral sodium oxalate solution to generate a homogeneous and adherent polypyrrole film. The growth of these films was facilitated by the initial oxidation of the copper electrode in the oxalate solution to generate a copper oxalate pseudo-passive layer. This layer was sufficiently protective to inhibit further dissolution of the copper electrode and sufficiently conductive to enable the electropolymerization of pyrrole at the interface, and the generation of an adherent polypyrrole film. These films remained stable and conducting for periods exceeding eight days and exhibited significant corrosion protection properties in acidified and neutral 0.1 mol dm⁻³ NaCl solutions even on polarization to high anodic potentials.     

Characterisation and corrosion protection properties of polypyrrole electropolymerised onto aluminium in the presence of molybdate and nitrate

This paper describes the first attempts for the electrosynthesis of polypyrrole films containing molybdate onto aluminium electrodes. Electrogeneration was carried out in an alkaline solution in the presence of molybdate, nitrate and the monomer. The optimum concentrations for electropolymerisation were chosen in order to improve the corrosion protection of the substrate. The coatings were characterised by SEM/EDX and IR spectroscopy and the cyclic voltammetric response of the film is discussed. Pitting corrosion resistance was studied by means of open circuit potential and potentiodynamic measurements. The results presented below show that molybdate remains entrapped into the polymer matrix, providing greater resistance to breakdown of passivity in chloride media.     

高性能防锈颜料磷酸锌的研制

采用液-液直接法,利用氧化锌和磷酸来生产磷酸锌。通过控制氧化锌悬浮液的加料速度、分散剂的用量、复合表面改性剂的用量,用吸油量、磷酸锌含量、粒度分布和耐盐雾性能来表征磷酸锌防锈颜料的最佳制备工艺。     

Comparative electrochemical studies of zinc chromate and zinc phosphate as corrosion inhibitors for zinc

The anticorrosive performance of two inhibitive pigments, zinc chromate and zinc phosphate, was compared using electrochemical impedance spectroscopy (EIS) and the scanning vibrating electrode technique (SVET) in pigment extracts in 0.1 M NaCl. It was observed that zinc was protected from corrosion in both extracts. In tests using hot dip galvanised steel painted with an epoxy primer incorporating the pigments, the SVET detected the anodic and cathodic distribution along the scribes, although no significant differences were observed among the various primers. On the contrary, EIS was able to distinguish processes occurring on the metal surface exposed by the scribe in different samples. For primers with anticorrosive pigment, a time constant at high frequencies was attributed to a layer of protective nature, probably formed by metal ions from the substrate and inhibitive ions leached from the anticorrosive pigments.     

Electrorheological properties of thermo-oxidative polypyrrole nanofibers

Using a chemical oxidative polymerization, polypyrrole (PPy) nanofibers were synthesized. After further thermo-oxidative treatment in air, the conductivity of PPy nanofibers was adjusted to a suitable level for use as a non-conventional nanofiber-based electrorheological (ER) suspension. Under electric fields, rheological properties of thermo-oxidative PPy nanofiber suspension were characterized. It showed that the nanofiber suspension possessed notable ER effect and low current density. Especially, the yield stress and shear modulus of nanofiber suspension were stronger than that of conventional granular suspension at the same volume fraction though the off-field viscosity of former was lower than that of latter. The ER effect and current density of thermo-oxidative PPy nanofiber suspension depended on the thermo-oxidative time and the nanofibers obtained after treatment for 3-5 h at 240 °C exhibited the optimal ER performances. It also showed that the thermo-oxidative PPy nanofiber suspension could maintain good ER properties within a wide operating temperature range of 25-115 °C.