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Application of carbonic materials as catalysts has recently been considered due to some advantages like tunable molecular structures, easy synthesis methods, abundance, and high tolerance in acidic and alkaline media. Here, a new metal-free electrocatalyst of halogenated reduced graphene oxide was prepared using cyclic voltammetry X (F, Br, and I)-RGO electrodeposition method. The prepared electrocatalysts were studied as a novel metal-free electrocatalyst for the hydrogen evolution reaction, and the presence of several halogen and oxygen functional groups on the surface of nanosheets was verified by the furrier transform infra-red, FT-IR, spectroscopy, and the presence of doped halogens on the RGO surface was confirmed by energy-dispersive X-ray, EDX, spectroscopy. The structural features and surface morphology of electrocatalysts were investigated by scanning electron microscopy (SEM) analysis. The electrochemical treatment of the X (F, Br, I)-RGO electrode was studied by some techniques like electrochemical impedance spectroscopy, EIS, chronoamperometry, CA, and linear sweep voltammetry, LSV. The X (F, Br, I)-RGO catalyst showed a lower onset potential (−0.81 V. vs. SHE), higher exchange current density (3.1 × ×10−1 mA cm−2), and lower charge transfer resistance (1.09 Ω cm2) related to the RGO catalyst due to the high active sites by heteroatoms and graphene nanosheets. [Display omitted] • One-step electrochemical method was used to synthesize the X-RGO electrode. • Introducing halogens to the carbon matrix created new active sites around the RGO. • An inexpensive metal-free catalyst and electrochemical synthesis was introduced. • X-RGO increased the electrocatalytic activity of HER compared to non-halogenated. [ABSTRACT FROM AUTHOR]

Factors such as inhibitor concentration, solution hydrodynamics, and temperature influence the performance of corrosion inhibitor mixtures. The simultaneous studying of the impact of different factors is a time- and cost-consuming process. The use of experimental design methods can be useful in minimizing the number of experiments and finding local optimized conditions for factors under the investigation. In the present work, the inhibition performance of a three-component inhibitor mixture against corrosion of St37 steel rotating disk electrode, RDE, was studied. The mixture was composed of citric acid, lanthanum(III) nitrate, and tetrabutylammonium perchlorate. In order to decrease the number of experiments, the L16 Taguchi orthogonal array was used. The 'control factors' were the concentration of each component and the rotation rate of RDE and the 'response factor' was the inhibition efficiency. The scanning electron microscopy and energy dispersive x-ray spectroscopy techniques verified the formation of islands of adsorbed citrate complexes with lanthanum ions and insoluble lanthanum(III) hydroxide. From the Taguchi analysis results the mixture of 0.50 mM lanthanum(III) nitrate, 0.50 mM citric acid, and 2.0 mM tetrabutylammonium perchlorate under the electrode rotation rate of 1000 rpm was found as optimum conditions. [ABSTRACT FROM AUTHOR]

In this research, the nanocomposite coatings comprising the polypyrrole-nanodiamond, PPy-ND, on St-12 steel electrodes were electro-synthesized using in situ polymerization process under ultrasonic irradiation. The corrosion protection performance and morphology characterization of prepared coatings were investigated by electrochemical methods and scanning electron microscopy, SEM, respectively. Also, the experimental design was employed to determine the best values considering the effective parameters such as the concentration of nanoparticles, the applied current density and synthesis time to achieve the most protective films. A response surface methodology, RSM, involving a central composite design, CCD, was applied to the modeling and optimization of the PPy-ND nanocomposite deposition. Pareto graphic analysis of the parameters indicated that the applied current density and some of the interactions were effective on the response. The electrochemical results proved that the embedment of diamond nanoparticle, DNP, improves the corrosion resistance of PPy coatings significantly. Therefore, desirable correlation exists between predicted data and experimental results. [ABSTRACT FROM AUTHOR]

ABSTRACT The electrochemical and sonoelectrochemical synthesis of polypyrrole (PPy) on St-12 steel was achieved in an oxalic acid medium by using a galvanostatic method with a current density of 4 mA/cm2. Direct application of low-frequency ultrasound led to more compact and more homogeneous surface structures for PPy. The corrosion behavior of the coatings was studied through open circuit potential-time curves, potentiodynamic polarization technique, and electrochemical impedance spectroscopy measurements in NaCl 3.5% solution. The Kramers-Kronig transformations were applied to evaluate the validity of the impedance data. The results showed that the coating resistance ( Rcoat), corrosion resistance ( Rcorr), and warburge resistance of ultrasonically prepared samples were higher than that of nonultrasonically synthesized PPy. With the help of scanning electron microscopy, we investigated the effects of the ultrasonic irradiation on the morphology and the results reveal that the sonoelectrochemical synthesis method yielded strongly adherent and smooth coats. [ABSTRACT FROM AUTHOR]

This work describes a new sonoelectrochemical synthesis method of novel composite materials based on silicon nitride (SiN) nanoparticles and intrinsically conducting polypyrrole (PPy). The sonoelectrochemical synthesis of polypyrrole coating and polypyrrole-silicon nitride (PPy-SiN) nanocomposite performed and corrosion behavior of these coatings on St-12 steel was studied by electrochemical methods. A design of experiment (DOE) technique using the Taguchi method has been applied to optimize the affecting factors on the sonoelectrochemical synthesis of PPy-SiN nanocomposite such as current density, synthesis time and amount of nanoparticles. The corrosion protection of St-12 steel by polypyrrole and polypyrrole-SiN nanocomposite coatings were investigated by open circuit potential (OCP) time trends, potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS) in NaCl 3.5% solution. The Kramers-Kronig transformation (KK) was applied to evaluate the validity of the experimental impedance data. The results prove that the addition of nanoparticles increased corrosion resistance of coatings and improved the surface morphology. Scanning electron microscopy (SEM) images reveal that the nanocomposite coatings form compact, homogenous and dense films on the St-12 steel surfaces. [ABSTRACT FROM AUTHOR]

Ni-Cu-P/nano-Al2O3 composite coatings are prepared on mild steel from an alkaline electroless plating bath containing different concentrations of Al2O3 nanoparticles. The protective effect of codeposited nanoparticles on the corrosion behaviour of the coatings is studied in 0.5 M H2SO4 solution. The electrochemical methods, that is, electrochemical noise (ECN), electrochemical impedance spectroscopy (EIS), and polarization measurements, are used to characterize the corrosion properties of the coatings. The results show that the inclusion of nanosized particles leads to significant improvement of corrosion resistance of the coatings. The highest corrosion resistance is obtained at 20 ppm of nanoparticles concentration in the plating bath. The ECN measurements results are in good agreement with results obtained from two other electrochemical methods after trend removal. The SEM images prove that nano-Al2O3 particles were embedded in the Ni-Cu-P matrix and are dispersed uniformly on the coating surface. [ABSTRACT FROM AUTHOR]

Zn-Ni alloy coatings were electroplated on steel after an appropriate pretreatment from tartrate cyanide free alkaline bath. Zn-Ni coatings were obtained with a derivative of imidazol as a brightener agent to form fine grain particles. The Zn-Ni alloy coatings were analysed for phase structure by X-ray diffraction. A cerium based chemical conversion process was developed as an alternative to the chromate process. The cerium conversion coatings improved the corrosion performance. The corrosion behaviour of bare and treated Zn-Ni alloy coatings on steel was evaluated during exposure to 0·5 N NaCl using Tafel polarisation and electrochemical impedance spectroscopy measurements. The morphology and corrosion performance of conversion coatings generated on Zn-Ni alloy coatings in Cr(VI) and Ce(III) treatments were studied and compared. This process may be useful as primer for paints and polymer coatings on steel. [ABSTRACT FROM AUTHOR]

The hydrodynamic conditions and fluid flow are important factors that affect the corrosion of metals. They also influence the inhibition performance of different corrosion inhibitors. In this paper, the corrosion behavior of St52-3 rotating disc electrode, RDE, in NaCl solution containing ZnSO4 salt, as a cathodic inorganic corrosion inhibitor, has been studied under different hydrodynamic conditions. Two electrochemical methods, including potentiodynamic polarization and electrochemical impedance spectroscopy, have been used. The effects of solution hydrodynamic on the open Circuit potential, polarization curves and electrochemical impedance diagrams of the steel RDE in blank NaCl solution as well as in the solution containing ZnSO4 have been considered. It has been shown that ZnSO4 inhibits the corrosion of steel in NaCl solution. By increasing the rotational speed, in the absence and presence of inhibitor, the corrosion current density increased and charge transfer resistance decreased. ZnSO4 had relatively low efficiency in stagnant conditions but its influence improved significantly under hydrodynamic conditions. It was mainly attributed to an increase in Zn2+ ions mass transport towards electrode surface, which leads to the formation of more protective films and therefore, enhances the protection against corrosion. [ABSTRACT FROM AUTHOR]

The removal of Reactive red 43, as a model pollutant, and some organic dyes with different structures by electrocoagulation process was investigated using iron (EC-Fe) and aluminum (EC-Al) anodes to explain dyes removal mechanism differences in EC-Fe and EC-Al processes. First, the effects of current density, electrolysis time and pH on the removal of Reactive Red 43were studied. The maximum removal efficiency (RE) was obtained in relatively acidic medium (pH = 4.25) in the first 12 minutes of EC-Al. While, in EC-Fe, a significant lag time between the starting of the process and initiation of considerable dye removal was observed. The color RE was supplemented with determining the RE of chemical oxygen demand. The COD values were determined for decolorization of solution containing 50 mg/L of RR43 and after 24 min of processes when the applied current density to monopolar batch electrochemical reactor was 25 A/m2. The COD removal efficiencies for the mentioned conditions were 73.92% and 97.12% for EC-Al and EC-Fe processes, respectively. The kinetics studies were carried out for both EC-Al and EC-Fe processes. In the similar operational conditions, the removal of basic dyes was not considerable by EC-Al. However, the RE of anionic dyes was improved with the addition of the number of sulfonate substituted groups. The maximum RE of all cationic and anionic dyes (RE > 90%) was achieved using EC-Fe. The enmeshment of dyes on iron oxide/hydroxide precipitates and charge neutralization were the main removal mechanisms in EC-Fe and EC-Al processes, respectively. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 547-556, 2013 [ABSTRACT FROM AUTHOR]