Denise Schermann Azambuja

Enlarged electrochemical window in dialkyl-imidazolium cation based room-temperature air and water-stable molten salts

The electrochemical windows of the ionic liquids 1-n-butyl-3-methyl imidazolium tetrafluoroborate (BMI+)(BF4−) and 1-butyl-3-methyl imidazolium hexafluorophosphate (BMI+)(PF6−) have been investigated at platinum, vitreous carbon, tungsten and gold electrodes. The lowest current densities and widest electrochemical windows were found on tungsten and vitreous carbon 6.10 and 5.45 V for (BMI+)(BF4−) and >7.10 and 6.35 V for (BMI+)(PF6−), respectively.

Electrochemical studies of propargyl alcohol as corrosion inhibitor for nickel, copper, and copper/nickel (55/45) alloy

Abstract The electrochemical behaviour of copper, nickel and copper/nickel (Cu55/Ni45) alloy in 0.50 M H2SO4 in the absence and presence of propargyl alcohol has been studied. The results indicate that the electrochemical behaviour of the copper/nickel alloy is similar to that of nickel. The interaction between the electrode surface and the organic compound is a relatively fast process and depends on the adsorption potential and alcohol concentration. Anodic currents associated with the electrooxidation of the metals decrease in the presence of propargyl alcohol. Differences in inhibition experience by the three electrodes are discussed in terms of cyclic voltammetry, potentiometry and impedance measurements.

Corrosion inhibition of copper in chloride solutions by pyrazole

Abstract The corrosion inhibition of copper in 0.1 M HCl in the presence of pyrazole was studied using potentiodynamic techniques with rotating disc and rotating ring disc electrode (RRDE). It was observed that the presence of pyrazole changes the mechanism of Cu dissolution in 0.1 M HCl. RRDE measurements showed that Cu+ was detected in the whole potential range studied, while Cu+2 was formed only at high anodic overpotentials. The addition of pyrazole decreases the rate of cuprous species formed and increases that of cupric species. Pyrazole behaves like a cathodic inhibitor and the inhibition efficiency is influenced by mass transport.

Hybrid polythiophene–clay exfoliated nanocomposites for ultracapacitor devices

Exfoliated nanocomposites of poly(3,4-ethylenedioxythiophene) (PEDOT) and montmorillonite (MMT) have been prepared by in situ anodic polymerization, concentrations of clay ranging from 5% w/w to 50% w/w being included in the aqueous polymerization medium. The morphology, electrical conductivity, adherence, thermal stability, charge storage, specific capacitance, electrostability, doping level and band gap have been determined for the different PEDOT–MMT nanocomposites and compared with those of pristine PEDOT. Many of these properties have been found to depend on both the concentration of clay and the thickness (micrometric or nanometric) of the generated films. Types I and II ultracapacitors have been fabricated using nanometric and micrometric films of PEDOT and PEDOT–MMT. The properties of such devices have been characterized and compared with those reported in the literature for ultracapacitors fabricated using nanocomposites of PEDOT and other inorganic materials. Both nanometric and micrometric type II ultracapacitors, which correspond to an asymmetric configuration of PEDOT and PEDOT–MMT films, have been found to present the better properties (e.g. the specific capacitance for nanometric and micrometric devices is 429 and 116 F g−1, respectively), evidencing the favorable effect of the clay. Finally, the effects of the electrochemical degradation on the ultracapacitors have been rationalized using electrochemical impedance spectroscopy.

Potentiodynamic tests and electrochemical impedance spectroscopy of injection molded 316L steel in NaCl solution

Abstract Cyclic polarization tests of injection molded 316L steel were carried out in 3% NaCl solution. The microstructure of the as-tested samples was studied by optical and scanning electron microscopy. The corrosion resistance of injection molded 316L steel was also evaluated studying the evolution of electrochemical impedance spectroscopy at the open-circuit potential for immersion periods varying from 1 to 78 days in aerated salt solution. The penetration of the electrolyte solution through surface open pores as a function of the immersion time has also been addressed so the effect of porosity on the corrosion behavior was investigated. The results demonstrated that the corrosion resistance of the injected steel is affected by the presence of open pores, as they act towards increasing the effective surface area of the material. This fact was confirmed by an increase in the corresponding value of the double layer capacitance, C dc , and a decrease in the value of the charge transfer resistance, R t .

Measuring the Proton Conductivity of Ion-Exchange Membranes Using Electrochemical Impedance Spectroscopy and Through-Plane Cell

The role of the incorporation of conducting polymer (CP), doped with different sulfonic acid organic molecules, in polystyrene (PS) and high-impact polystyrene (HIPS) with poly(styrene-ethylene-butylene) (SEBS) triblock copolymer has been investigated. Two factors associated with this model membrane system are addressed: (i) the influence of the presence of a low concentration of doped conducting polymer and (ii) the influence of the membrane preparation method. Membrane characterization and bulk conductivity measurements allowed the conclusion that proton conductivity has been promoted by the addition of CP; the best results were achieved for PAni-CSA, in either PS/SEBS or HIPS/SEBS blends. Additionally, the water uptake only decreased with the addition of PAni-doped molecules compared to the pure copolymer, without loss of ion-exchange capacity (IEC). Electrodialysis efficiency for HIPS/SEBS (before annealing) is higher than that for HIPS/SEBS (after annealing), indicating that membrane preparation method is crucial. Finally, through-plane cell arrangement proved to be an effective, quick, and time-saving tool for studying the main resistance parameters of isolating polymers, which is useful for application in industry and research laboratories working with membranes for electrodialysis or fuel cells.

Corrosion resistance of steel coated with Ti/TiN multilayers

Abstract The corrosion resistance behaviour of steel coated with TiN thin films deposited by physical vapour deposition (PVD) has been studied by electrochemical techniques in de-aerated 1 M sodium acetate solution at pH 5.6. Two different types of coatings deposited on carbon steel samples have been studied: (1) multilayered coatings of Ti/TiN in which the interfaces are compositionally abrupt, and (2) multilayered coatings of Ti/TiN in which there is a mixture between the two materials at the interfaces leading to gradual composition interfaces. The electrochemical results obtained have been correlated to structural defects studied by scanning electron microscopy. It has been observed that the corrosion resistance of coated steel was higher than the substrate resistance. The graded composition interface coatings showed a more protective character than the sharp interface. The corrosion resistance is mainly controlled by the occurrence of coatings defects and their presence can be easily detected by electrochemical measurements.

Sol–gel hybrid films based on organosilane and montmorillonite for corrosion inhibition of AA2024

The present work reports the production of films on AA2024-T3 composed of vinyltrimethoxysilane (VTMS)/tetraethylorthosilicate (TEOS) with incorporation of montmorillonite (sodium montmorillonite and montmorillonite modified with quaternary ammonium salt, abbreviated Na and 30B, respectively), generated by the sol-gel process. According to FT-IR analyses the incorporation of montmorillonite does not affect silica network. Electrochemical characterization was performed by electrochemical impedance spectroscopy measurement in 0.05 mol L(-1) NaCl solution. Results indicate that montmorillonite incorporation improves the corrosion protection compared to the non-modified system. Scanning electron microscopy micrographs reveal that high concentrations of montmorillonite provide agglomerations on the metallic surface, which is in detriment of the anticorrosive performance. The VTMS/TEOS/30B films with the lowest concentration (22 mg L(-1)) of embedded clay provide the highest corrosion protection.

Poly(3,4-ethylenedioxythiophene) on self-assembled alkanethiol monolayers for corrosion protection

Self-assembled monolayers (SAMs) of octanethiol and dodecanethiol were used to modify the stainless steel substrates for electrodepositing poly(3,4-ethyledioxythiophene) (PEDOT), a well known polythiophene derivative. Although the influence of the alkanethiol monolayers on the morphology and topology of micrometric (thickness: 2.25–2.35 μm) PEDOT films is practically negligible, they increase significantly the ability to store charge and the adherence. In contrast, treated substrates not only enhance the electrochemical properties of ultra-thin PEDOT films (thickness: 150–350 nm) but also affect significantly the thickness, roughness, porosity, morphology and topology. Such changes depend on both the length of the alkyl chain in the alkanethiol and the incubation period used for the preparation of the SAMs. Finally, the protection against corrosion imparted by PEDOT films deposited on treated substrates has been examined and compared with that obtained using PEDOT deposited on bare stainless steel electrodes. Inhibition of the corrosion in a 3.5% NaCl solution was found to be considerably higher when PEDOT is deposited on treated electrodes, which has been attributed, in addition to the barrier effect produced by the SAMs, to the structural changes induced at the first stages of the electropolymerization.

Electrochemical behaviour of iron in neutral solutions of acetate and benzoate anions

The electrochemical behaviour of iron in pH 6 aqueous solutions of benzoate and acetate anions mixed in varying concentrations and constant ionic strength was investigated. For that purpose cyclic voltammetric experiments were carried out at a disc electrode either static and/or rotating. A high surface coverage is observed in the presence of benzoate anions, thus favouring the establishment of a passive state. The overall process is discussed in terms of a three-dimensional film, the growth mechanism of which is under diffusion and migration control. It was also observed that the addition of chloride ions to the mixed electrolyte solutions containing increasing benzoate concentration shifts the breakdown potential and the repassivation potential toward more positive values.