Papers by Keyword: Electrochemical Behaviour

Abstract: The initial stages of copper electrodeposition in acid copper sulphate/sodium citrate bath were investigated with varying copper and sodium citrate concentrations. Different electrochemical measurements, including linear sweep voltammetry, cyclic voltammetry, and chronoamperometry were introduced to the study. The Scharifker-Hills model was introduced to identify the nucleation model with analysing current transients. It was observed that the increase of copper ions inhibited the cathodic polarization behaviour for the reduction of ions. On the contrary, sodium citrate promoted the cathodic polarization behaviour. The chronoamperometry results indicated that without the sodium citrate, the nucleation process corresponded to instantaneous nucleation and three-dimensional diffusion limited growth, although obvious deviations were observed. While the addition of sodium citrate changed the deviations and caused that the initial deposition kinetics followed well with the mechanism of instantaneous nucleation.

Abstract: This paper compares the microstructure and electrochemical properties of the diamond-like carbon films obtained by two different deposition methods - microwave electron cyclotron resonance plasma enhanced chemical vapor deposition (MWECR-PECVD) techniques and electro-deposition – chosen for their low cost and capacity to produce films. The microstructure of the DLC films are investigated by Raman spectroscopy, FTIR spectroscopy, and electrochemical behavior is investigated by potentiodynamic and electrochemical impedance spectroscopy (EIS). Raman spectroscopy indicates that all the films deposited by different techniques show amorphous structure and typical characteristic of DLC film. FTIR spectrum results indicate that these DLC films are a-C:H films. As a result of EIS, the DLC films made by different methods showed obviously different electrochemical characters. The obtained results show that the DLC films deposited using the PECVD methods provided the better results, presenting a high corrosion resistance , high adherence to substrate, and a denser and more uniform surface.

Abstract: Micro-TiO₂ and nanoTiO₂ dispersed Al 7075 composites have been synthesized by mechanical milling followed by cold compaction and sintering. The compressibility of the nanocomposites is less than the micro composite, but sintered density of the nanocomposite is higher that the microcomposite. Nanocomposite shows better hardness than microcomposite. However, both types of composites do not show artificial ageing characteristics like unreinforced Al 7075 alloy. Microstructural analysis through XRD and TEM reveals that the formation of MgTiO₃ and ZnO near TiO₂-Al 7075 matrix interface causes depletion of Mg and Zn in the Al 7075 matrix. This suppresses GP zone formation and shows almost no age hardenable characteristic. Potentiodynamic electrochemical polarisation study shows that the corrosion potential (E_corr) has shifted towards noble direction with the addition of TiO₂ in the composite.

Abstract: The electrochemical behaviour of the rehealing oxide scales on the K52 nanocrystalline coatings had been studied by polarization curves. The results indicated that the oxide scales formed on the nano-coating exhibited rehealing ability after pitting corrosion, and the coating still had excellent corrosion resistance. The rehealing ability was enhanced with prolonged re-oxidation time. EDX analyses revealed that the oxide scales within the pits were composed of mixed-oxides (Cr2O3, Al2O3 and TiO2). The mixed-oxides were made up of two layers: the external oxide layer was composed of Cr2O3 and TiO2 and the internal oxide layer was Al2O3.

Abstract: Polarization curves, corrosion potential, scanning electron microscopy (SEM) were adopted to investigate the corrosion behaviors of QSn4-3 under two kinds of marine advantage bacteria (anaerobic SRB and facultative anaerobic Vibrio natriegens) environment. The results show that the microbial film has some effects on inhibiting corrosion of QSn4-3 at the early stage of corrosion; the existence of marine microorganisms accelerates the corrosion process of QSn4-3; the combined action of SRB and V.natriegens accelerates the corrosion obviously and QSn4-3 coupon is more prone to pitting corrosion.

Abstract: The modified electrodes of Mo(W)-S-Ag cluster compounds films on silver surface were investigated by FT-IR, FT-Raman and XPS. The new modified electrodes were applied to the catalytic oxidation of ascorbic acid. This sort of catalytic effects can be inferred because the oxidation peak potentials of ascorbic acid moved to more negation compared with the bare Ag electrode and the oxidation peak currents increased with the increasing of ascorbic acid concentration. The overpotentials of ascorbic acid were significantly reduced. The cycle voltammograms (CV) measurement revealed the linear relationship between the oxidation peak current and the concentration of ascorbic acid ranging among 0.001~ 0.06 mol.L-1.

Abstract: An attempt has been made to increase the corrosion resistance properties of medium steel substrate by using silica sol.The results show that: sol-gel method can increase corrosion resistance of phosphating coating. PS(silicon sol coated after phosphating )’s corrosion potential reduced more than P(phosphating sample)’s and its corrosion density also reduced.Polarizationg resistance of PS can improved many times.R2 of PS more reduced than P,but R3 improved more than ten times and R4 improved over sixty times by using equivalent circuit to fit EIS measurement. Corrosion resistance of PS was higher than that of P.

Abstract: Zirconium ethoxide was synthesized by direct electrochemical reaction of anhydrous ethanol with sacrificial zirconium anode in the presence of tetraethylammonium chlorides (Et4NCl) as a conductive agent. The samples of products were characterized by Fourier transform infrared spectra (FT-IR) and Proton nuclear magnetic resonance spectroscopy (1H-NMR). The experiment results show that direct electrochemical synthesis of zirconium ethoxide has high current efficiency and abundant synthetic product compared with the conventional chemical methods. The behaviors of Zr in Et4NCl ethanol solutions were measured through potentiodynamic polarization, cyclic voltammetry, and potentiostatic current-time transient techniques. Effects of the temperature, scanning rate and the Et4NCl concentration were investigated. The results indicate that the electrochemical dissolution of the metal in anhydrous ethanol is a process of corrosive pitting. The rate of pit nucleation and pit growth increases with increasing of temperature and the Et4NCl concentration.

Abstract: Nanostructured manganese oxides (Mn₃O₄, MnOOH) were successfully prepared by a hydrothermal method using MnCl₂ as manganese source, NaOH as precipitation agent and H₂O₂ as oxidant. The composition and morphology of the products were determined by the dripping speed of NaOH solution, the adding order of reactant and the hydrothermal time. Single phase of Mn₃O₄ nanoparticles can be prepared by dropwise addition of the NaOH solution to the solution of MnCl₂ and H₂O₂. While single phase of MnOOH nanorods can be obtained by pouring the NaOH solution into the reaction system quickly or changing the adding order of NaOH and H₂O₂. When the dripping speed of NaOH solution was 6mL/min, and an appropriate amount of surfactant (C₁₈H₂₉NaO₃S) was added, Mn₃O₄ nanorods can be obtained. The hydrothermal method can be readily controlled to synthesize Mn₃O₄ and MnOOH with different morphologies. The Mn₃O₄ sample had higher capacitance than the MnOOH sample. The morphologies of these samples had little effect on their electrochemical performance.

Abstract: The potentiodynamic polarization and cyclic voltommogroms studies were carried out on the copper with micro-addition of Cr and Zr in solutions of 0.5M NaCl, 0.5M NaOH and 0.5M HCl at room temperature. The corrosion resistance of pure copper is deteriorated with addition of the alloying elements Cr and Zr. Significant reducing in the corrosion resistance is observed when Cr and Zr are added simultaneously. Moreover, the lowest corrosion current density is obtained in the NaCl solution followed by the NaOH solution and HCl solution. Compared with the different effect on the passive layer in the NaCl solution, the micro-addition of Cr and Zr leads to the increasing of the corrosion resistance for the passive layer in 0.5M NaOH solution and 0.5M HCl solution.