Tafel Test Research Articles

Hydrothermal synthesis of urchin-like reduced graphene oxide–CdS and its electrochemical property

Reduced graphene oxide–cadmium sulfide (rGO–CdS) hybrid was prepared by a hydrothermal method from GO, Cd (Ac)2⋅2H2O, and CH4N2S. The XRD pattern indicated that CdS within the cubic crystallographic structure was obtained and the XPS spectrum showed that GO was reduced to rGO during the hydrothermal process. The morphology and microstructure of the as-prepared hybrid was characterized by SEM and TEM measurements. It was revealed that the obtained CdS particles were in a monodispersed urchin-like morphology and precipitated on the rGO layers. In order to evaluate the electrochemistry catalytic properties of the hybrid, a Tafel test was performed and indicated that the hybrid has a comparative activity to Pt. It was expected that the rGO–CdS could be a promising candidate for counter electrodes (CEs) in dye-sensitized solar cells (DSSCs).

Investigation of corrosion protection performance of epoxy coatings modified by polyaniline/clay nanocomposites on steel surfaces

In this study, polyaniline (PANI) and polyaniline/clay nanocomposites were prepared via in situ oxidative polymerization. The morphology of nanocomposites structures was investigated by X-ray diffraction (XRD). The chemical structures of PANI and PANI/clay nanocomposites were examined via Fourier transform infrared (FT-IR) spectroscopy. Polyaniline-based pigments were introduced into epoxy paint and applied on steel substrates. The effect of clay addition and the type of clay cation, including Na+ in natural clay (MMT) and alkyl ammonium ions in organo-modified montmorillonite (OMMT), on the anticorrosion performance of epoxy-based coatings was investigated through electrochemical Tafel test, electrochemical impedance spectroscopy and immersion measurements in NaCl solution. The stability of the adhesion of the neat and modified epoxy coatings to the steel surface was also examined. The results indicated that introduction of PANI/OMMT nanocomposite into epoxy paint results in improved anticorrosion properties in comparison with PANI/MMT and neat PANI.

Evaluation of the protective effect of polysiloxane coating on pyrite with electrochemical techniques

The efficiency of polysiloxane coating to suppress the pyrite oxidation under environmentally relevant conditions was investigated with electrochemical techniques. Cyclic voltammogram, Nyquist plot or Tafel test were preformed in the conditions of different polysiloxane proportions in modifying agent, pH values, Fe3+ concentrations and volumes of water impact. The increased proportion of polysiloxane in the modifying agent would enhance the protective effect of the coating. The modifying agent with the least proportion of polysiloxane was used in subsequent experiments to illustrate the excellent passivation of polysiloxane. The results indicated that coating on the pyrite had good protective effect to resist the oxidation of pyrite in the aggressive condition of pH 2. Moreover, there were no distinctive differences in coated pyrite behaviors during anodic oxidation in solutions with different pH values. Furthermore, in a wide range of Fe3+ concentrations, the coating on the pyrite still showed good effect to retard the pyrite oxidation. Finally, the coating on the pyrite possessed good washing durability. Therefore, polysiloxane coating had great potential to develop a new AMD suppression strategy.

Electrochemical deposition and evaluation of electrically conductive polymer coating on biodegradable magnesium implants for neural applications

In an attempt to develop biodegradable, mechanically strong, biocompatible, and conductive nerve guidance conduits, pure magnesium (Mg) was used as the biodegradable substrate material to provide strength while the conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT) was used as a conductive coating material to control Mg degradation and improve cytocompatibility of Mg substrates. This study explored a series of electrochemical deposition conditions to produce a uniform, consistent PEDOT coating on large three-dimensional Mg samples. A concentration of 1 M 3,4-ethylenedioxythiophene in ionic liquid was sufficient for coating Mg samples with a size of 5 × 5 × 0.25 mm. Both cyclic voltammetry (CV) and chronoamperometry coating methods produced adequate coverage and uniform PEDOT coating. Low-cost stainless steel and copper electrodes can be used to deposit PEDOT coatings as effectively as platinum and silver/silver chloride electrodes. Five cycles of CV with the potential ranging from -0.5 to 2.0 V for 200 s per cycle were used to produce consistent coatings for further evaluation. Scanning electron micrographs showed the micro-porous structure of PEDOT coatings. Energy dispersive X-ray spectroscopy showed the peaks of sulfur, carbon, and oxygen, indicating sufficient PEDOT coating. Adhesion strength of the coating was measured using the tape test following the ASTM-D 3359 standard. The adhesion strength of PEDOT coating was within the classifications of 3B to 4B. Tafel tests of the PEDOT coated Mg showed a corrosion current (I(CORR)) of 6.14 × 10(-5) A as compared with I(CORR) of 9.08 × 10(-4) A for non-coated Mg. The calculated corrosion rate for the PEDOT coated Mg was 2.64 mm/year, much slower than 38.98 mm/year for the non-coated Mg.

Enhanced performance and capacitance behavior of anode by rolling Fe3O4 into activated carbon in microbial fuel cells

Fe3O4 was added into the anode to improve the performance of microbial fuel cells (MFCs). Stainless steel mesh (SSM), activated carbon (AC) with SSM (AcM) and Fe3O4 added AcM (AcFeM) anodes had been made and investigated by electrochemical measurements. The maximum power density of AcFeM anode (809±5mW/m2) is 22% higher than that of AcM (664±17mW/m2), and 56 times higher than that of SSM anode (14±0.3mW/m2). Tafel tests indicate that the anode modified by Fe3O4 is kinetically more advantageous. It is demonstrated for the first time that the capacitance of anode increased after the addition of Fe3O4. With 10min of interruption, AcFeM exhibites a 41% higher cumulative charge of 3566±32C/m2 and a 32% higher net capacitance charge of 389±18C/m2 than those of the AcM control (2529±22 and 294±30C/m2), indicating that the improvement of anode performance can be also attributed to the enhancement of capacitance.

Epoxy Modified with TDI to Cure Active Hydrogen Groups: Synthesis and Characterization

Study on isocyanate-terminated prepolymer prepared by the reaction of toluene diisocyanate (TDI) with the hydroxy of epoxy resin. By the characteristics that isocyanate-group reacts with active hydrogen groups easily, the prepolymer could be as a curing agent for substance with active hydrogen groups like coal tar. IR spectra showed that the modification was achieved by cross-linking the hydroxy of epoxy resin and the isocyanate of TDI, but epoxy group had no change. In self-made coal tar coatings, the remaining isocyanate-groups played a curing agent role linking coal tar and epoxy resin. Tafel test showed the films with prepolymer was more corrosion resistance, combined the characteristics of the epoxy resin and coal tar.

Poly(N-vinylpyrrolidone) modified polyaniline/Na+-cloisite nanocomposite: Synthesis and characterization

A novel electrically conductive nanocomposite consisting of poly(N-vinylpyrrolidone) (PVP) modified polyaniline (PANI) and cloisite clay nanoparticles was obtained via insitu polymerization method. The synthesized nanocomposite was characterized using FT-IR, XRD, conductivity measurement and cyclic voltammetry techniques. The electrical conductivity measurements of prepared nanocomposite showed that the nanocomposite is electrically conductive. Also cyclic voltammetry studies revealed that the synthesized nanocomposite is electro active. Electrochemical corrosion studies including open circuit potential measurements and tafel tests were carried out in various corrosive environments to evaluate the anticorrosive property of the nanocomposite coating on iron samples. Results showed that the coating of this nanocomposite on iron was useful in decreasing corrosion current and corrosion rate of iron in comparison with bare iron and pure polyaniline coated samples. A positive shift in corrosion potential and a significant decrease in corrosion current were observed for nanocomposite coated iron samples in sodium chloride 3.5 %, hydrochloric acid 0.1 M and sulfuric acid 0.1 M solutions.

Ti-WC Nanocrystalline Coating Formed by Surface Mechanical Attrition Treatment Process on 316L Stainless Steel

Nanocrystalline coatings were performed on the surface of 316L stainless steel plates mechanically with a mixture of Ti and WC powders under vacuum conditions. The targets were replaced in the end of the high energy milling rig, while Ti-WC mixture was milled as usual. It is shown that the coatings are nanocrystalline in nature with narrow distribution of average size of nanocrystallites. X-ray diffraction and scanning electron microscopy (with energy-dispersive spectrometer) revealed that the top layer of the coatings is uniform. Microhardness, roughness and primary corrosion tests (tafel tests) proved enhancement of coated samples with respect to raw materials. Transmission electron microscope image of deformed surface confirmed surrounding of nanoparticles by dislocation loops after plastic deformation.

Electrochemical synthesis of bilayer coatings of poly( N-methylaniline) and polypyrrole on mild steel and their corrosion protection performances

Homopolymer and bilayer coatings of poly( N-methylaniline) (P NMA) and polypyrrole-dodecylsulfate (PPy-DS) have been electropolymerized on a mild steel (MS) surface by the potentiodynamic method in aqueous oxalic acid solutions. In order to include dodecylsulfate ion as dopant in the polypyrrole, sodium dodecylsulfate was also added to the polymerization solution of pyrrole. Characterization of coatings was carried out by the cyclic voltammetry, Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy (FESEM). Corrosion behavior of the polymer coated MS electrodes was investigated in highly aggressive 0.5 M HCl solution by the Tafel test and electrochemical impedance spectroscopy (EIS) techniques. Corrosion test revealed that among the protective coatings obtained, the P NMA/PPy-DS bilayer exhibited the best corrosion resistance at all immersion times.

Polyaniline coating on 304 stainless steel by electropolymerisation from aqueous NaOH solution for corrosion protection in NaCl medium

Polyaniline (PAn) coating was electrochemically synthesised on 304 stainless steel using cyclic voltammetry in 0·25M NaOH solution containing 0·1M aniline. Characterisation of the adhesive and stable PAn coating was carried out by cyclic voltammetry, Fourier transform infrared spectroscopy and scanning electron microscopy. The protective properties of PAn coating on 304 stainless steel were elucidated using linear anodic potentiodynamic polarisation and Tafel test in 3·5%NaCl solution. Linear anodic potentiodynamic polarisation test results proved that the PAn coating improved the degree of protection against pitting corrosion in NaCl solutions. Tafel test results showed that the PAn coating appeared to enhance protection for 304 stainless steel in 3·5%NaCl solution.

High Anticorrosion Nano Zn-Fe Coatings by Pulse Electrodepositing

Nano Zn-Fe coatings in a chloride electrolyte with additives by reverse pulse current were obtained and the anticorrosion was investigated. The morghology and crystal size of Zn-Fe alloy depositions were measured by scanning electron microscope and atom force microscope. Coatings with 30 nm or so crystal size was obtained with mean current density 9.0 A•dm-2, duty cycle 60%, frequency 500 Hz and time of negative to positive 30 ms ∶8 ms. It was detected by X-ray diffraction that the pulse plated coatings of Zn–Fe were mixtures of two phases, one of them being the α-phase and the other pure zinc or the α-phase with a significantly lower proportion of Fe. The pulse plated Zn-Fe coatings’ corrosion resistance was greatly improved compared with Zn-Fe coatings by direct current according to Tafel tests, saline immersion and salt spray tests. The anticorrosion of Zn-Fe coatings with 30 nm crystal size was 2~3 times than that of normal Zn-Fe alloy deposits.

Effect of fluxing chemical: An option for Zn–5wt.%Al alloy coating on wire surface by single hot dip process

The corrosion of wire is one of the primary causes for premature failure. The ideal way to overcome this problem is to provide corrosion protection right at the time of manufacturing. It is well established fact that Zn–5wt.% Al alloy coating on steel surface provides much better protection against corrosion than the conventional pure Zn coating. Conventional fluxing operation is done on wire surface using zinc and ammonium chloride mixture before dipping in molten zinc bath. Galvanization bath temperature of about 415°C for Zn–5wt.% Al alloy coating on wire surface develops black spots of AlCl3 when conventional flux is used. Double dip process is being followed for Zn alloy coating on wire surface due to non availability of suitable flux. An effort has been made to develop a suitable flux to obtain Zn–5wt.% Al alloy coating on wire surface by single hot dip process. A salt mixture (containing zinc, ammonium, sodium, potassium, cobalt and lead chloride) was formulated based on the decomposition temperature of individual chloride salts. Differential thermal and thermo gravimetric analysis indicate the temperatures for complete decomposition of conventional and formulated flux are 445 and 410°C, respectively. The lower decomposition temperature of formulated flux is ensured black spot free Zn–5wt.% Al alloy coating. Alloy coated wire consists of alternative layers of zinc rich and aluminium rich phases. The performance of alloy coated wires has been evaluated by salt spray and Tafel tests. The alloy coated wire shows around 4 times improvement of corrosion performance against aggressive chloride environment compared to pure zinc coated wire. This can be attributed to the fact that aluminium rich phase prevents dissolution of zinc rich phase.

Characterization of Ni-W/MWCNT nanocomposite layers formed by pulsed electrochemical deposition

Ni-W/MWCNT nanocomposite layers with high concentration and uniformly dispersed MWCNT nanoparticulates were formed by pulsed electrochemical deposition technique. Nanocomposite layers were analyzed by SEM, AFM, microhardness and tafel tests. Effect of frequency of pulsed current and concentration of MWCNT nanoparticulates in metallic matrix have been investigated on electrochemical and mechanical properties of obtained layers. It has been concluded that both of the electrochemical and mechanical properties of Ni-W/MWCNT nanocomposite layers formed by pulsed current were improved significantly with respect to Ni-W layer with out nanoparticulates. It was revealed that the obtained results were not only concerned by the concentration of MWCNT nanoparticulates in the nanocomposite layer, but also influenced by the distribution of nanoparticulates in metallic matrix.

Enhancing the Stability of PPy Film on Ti by PEG Incorporation

Composite films based on polypyrrole (PPy) and polyethylene glycol (PEG) were synthesized on titanium electrode, using various percentages of PEG, as the insulating material in order to enhance surface properties of the polymer composite films. The Fourier transform infrared spectroscopy (FT-IR) was performed to demonstrate the formation of a PPy-PEG composite film. The corrosion behaviour of coatings has been studied by Tafel tests and cyclic voltammetry. The PPy-PEG films/electrolyte interface was analyzed by electrochemical impedance spectroscopy (EIS) and the specific parameters of corresponding equivalent circuits were calculated. The polymeric layer morphology on titanium substrate has been evaluated using atomic force microscopy (AFM) and enhanced properties of the PPy-PEG films are discussed as the effect of PEG incorporation in the polypyrrole structure.

Electrodeposition of Polypyrrole/Poly(Styrene Sulphonate) Composite Coatings on Ti6Al7Nb Alloy

The aim of this work is to study the influence of surfactants concentration on pyrrole polimerization on Ti6Al7Nb alloy in order to improve the surface performance of such biomaterials. The electrochemical stability of the polypyrrole based composite coatings were evaluated in Hank's Balanced Salt Solution by Tafel tests, cycle voltammetry and electrochemical impedance spectroscopy (EIS). The surface analysis of composite coating type atomic force microscopy (AFM), was completed with an infrared structure evaluation. The coating properties such as electrochemical parameters, wettability and roughness can be controlled by changing the pyrrole/poly(styrene sulphonate) polymerization ratio.

Polybithiophene and its bilayers with polyaniline coatings on stainless steel by electropolymerization in aqueous medium

For the first time, electrosynthesis of polybithiophene (PBTh) and its bilayers with polyaniline (PAni) coatings on stainless steel (SS) in aqueous oxalic acid solutions containing monomer and sodium dodecyl sulfate (SDS) was carried out by potentiodynamic synthesis technique. Smooth and adherent films were obtained on the steel surfaces. Homopolymers and bilayers were characterized by cyclic voltammetry, FTIR, UV–vis spectroscopies and SEM. Homopolymers were also characterized by means of conductivity and the number average molecular weight measurements. The effects of the scanning potential limits on electrosynthesis of PBTh and its bilayer coatings were investigated. The test for corrosion protection of the polymer coated and uncoated SS substrates were performed in highly aggressive 0.5 M NaCl and 0.5 M HCl solutions by linear potentiodynamic polarization and Tafel test technique, respectively. Corrosion test revealed that among the protective coatings obtained, PBTh as homopolymer and PAni/PBTh as bilayer exhibited the most effective anticorrosive properties. According to linear potendynamic polarization test, the dissolution current of these coatings at 1.6 V decreased to 99.8% and 99.6% in NaCl solution, respectively, when compared to that of uncoated SS surfaces.

Electrochemical synthesis of poly( N-methylaniline) on an iron electrode and its corrosion performance

Synthesis of poly( N-methylaniline) (PNMA) on pure iron and Pt electrodes was carried out from aqueous 0.3 M oxalic acid solution containing 0.1 M N-methylaniline (NMA) by potentiodynamic and galvanostatic techniques. It was found that when compared to polyaniline (PAni) and its ring- and N-ethyl-substituted derivatives, PNMA can be electrosynthesized with lower upper scanning potential (upper potential limit, E upp) of 0.8 V vs. saturated calomel electrode (SCE) on an Fe electrode. PNMA coatings were characterized by electrochemical, scanning electron microscopy (SEM) and FTIR techniques. Linear anodic potentiodynamic polarization results proved that increasing the acidity of the polymerization solution causes more effective protection against corrosion in 0.5 M H 2SO 4 medium for PNMA. Moreover, PNMA exhibited similar protective properties with PAni under the same corrosion test conditions. Tafel test results reveal that the PNMA coating appears to enhance protection for iron in 0.5 M NaCl and 0.1 M HCl solutions. According to EIS results, the PNMA coating is able to offer protection to Fe electrodes in NaCl compared to that in HCl medium over a long immersion period.

Poly( N-ethylaniline) coatings on 304 stainless steel for corrosion protection in aqueous HCl and NaCl solutions

Poly( N-ethylaniline) (PNEA) coatings were grown by potentiodynamic synthesis technique on 304 stainless steel (SS) alloy from 0.1 M of N-ethylaniline (NEA) in 0.3 M oxalic acid solution. Characterization of adhesive and electroactive PNEA coatings was carried out by cyclic voltammetry, FT-IR spectroscopy and scanning electron microscopy (SEM) techniques. The protective properties of PNEA coatings on SS were elucidated using linear anodic potentiodynamic polarization, Tafel and electrochemical impedance spectroscopy (EIS) test techniques, in highly aggressive 0.5 M HCl and 0.5 M NaCl solutions. Linear anodic potentiodynamic polarization test results proved that PNEA coating improved the degree of protection against pitting corrosion in HCl and NaCl solutions. Tafel test results showed that PNEA coating appears to enhancement protection for SS in 0.5 M NaCl and 0.5 M HCl solutions. However, according to long-term EIS results, PNEA coating is better for the protection of SS electrodes during the long immersion period in NaCl compared to that in HCl medium.

Characterisation of coating on rebar surface using Hot-dip Zn and Zn-4.9Al-0.1 misch metal bath

The corrosion of rebar is one of the primary causes of premature deterioration of the concrete structure. The ideal option to overcome this situation would be to provide corrosion protection right at the time of manufacturing of the rebar before it is encased in the concrete and hence, warrants the use of corrosion resistance rebar. The present paper outlines characterisation of coating obtained on rebar surface from pure Zn and Zn-4.9Al-0.1 misch metal bath. The coating was characterised by SEM, EDS, Galvanostatic and XRD techniques. In case of pure Zn bath, distinct phases such as eta, zeta, delta and gamma 1 and gamma were identified in coating where as in case of Zn-4.9Al-0.1 misch metal bath no such distinctive phases were found. The coating obtained from Zn-4.9Al-0.1 misch metal bath was thinner and consisted of outer Al 2O 3 phase followed Zn–Al phase resulting in better ductility compare to the coating obtained from pure Zn bath. Comparative corrosion resistance performances of both types of coating respect to uncoated rebar were evaluated by salt spray and tafel test. were conducted in simulated aggressive chloride and concrete pore solution of coated and The coating obtained form Zn-4.9Al-0.1 misch metal bath was found to be more anodic and showed 1.5-3 times better corrosion resistance in concrete pore solution and 2.5 times better resistance against aggressive chloride attack compare to the coating obtained from pure Zn bath. Both the coatings dissolved in faster rate in highly alkaline environment (pH = 13.6) where as dissolution rate decreased with decrease of pH in pore solution. The sacrificial as well as barrier protection of Zn–Al alloy coating was found to be more effective than pure Zn coating. Both types of coated bars showed reduction in bond strength in concrete structure. It is attributed by the faster dissolution of the coating, leading to hydrogen gas evolution thereby creating a gap between the rebar surface and concrete structure.

Inhibition of corrosion of mild steel by homopolymer and bilayer coatings of polyaniline and polypyrrole

Homopolymers and bilayers of polyaniline (PAni) and polypyrrole (PPy) coatings have been electropolymerized on mild steel by potentiodynamic synthesis technique in aqueous oxalic acid solutions. Characterization of coatings was carried out by cyclic voltammetry. Corrosion behavior of the polymer coated mild steel electrodes was investigated using linear anodic potentiodynamic polarization, Tafel test and electrochemical impedance spectroscopy (EIS) techniques in various aqueous corrosive solutions. Corrosion test results clearly showed that PPy and PAni/PPy bilayer coatings served as a stable host matrix on mild steel against corrosion. However, bilayers of PAni and PPy did not exhibit good combined properties of each polymer, unlike expected. PPy exhibited the best corrosion resistance among all coatings.